ORCID Profile
0000-0001-6897-4651
Current Organisations
Lomonosov Moscow State University
,
Moscow State University
,
P.N. Lebedev Physical Institute of the Russian Academy of Sciences
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Publications
Evidence for the production of three massive vectorbosons in $pp$ collisions with the ATLAS detector
Publisher: Sissa Medialab
Date: 27-06-2019
DOI: 10.22323/1.352.0135
Determination of the parton distribution functions of the proton using diverse ATLAS data from pp collisions at $$\sqrt{s} = 7$$, 8 and 13 TeV
Publisher: Springer Science and Business Media LLC
Date: 05-2022
DOI: 10.1140/EPJC/S10052-022-10217-Z
Abstract: This paper presents an analysis at next-to-next-to-leading order in the theory of quantum chromodynamics for the determination of a new set of proton parton distribution functions using erse measurements in pp collisions at $$\\sqrt{s} = 7$$ s = 7 , 8 and 13 TeV, performed by the ATLAS experiment at the Large Hadron Collider, together with deep inelastic scattering data from ep collisions at the HERA collider. The ATLAS data sets considered are differential cross-section measurements of inclusive $$W^{\\pm }$$ W ± and $$Z/\\gamma ^*$$ Z / γ ∗ boson production, $$W^{\\pm }$$ W ± and Z boson production in association with jets, $$t\\bar{t}$$ t t ¯ production, inclusive jet production and direct photon production. In the analysis, particular attention is paid to the correlation of systematic uncertainties within and between the various ATLAS data sets and to the impact of model, theoretical and parameterisation uncertainties. The resulting set of parton distribution functions is called ATLASpdf21.
Correlations between flow and transverse momentum in
Xe + Xe
Publisher: American Physical Society (APS)
Date: 15-05-2023
Luminosity determination in pp collisions at $$\sqrt{s}=13$$ TeV using the ATLAS detector at the LHC
Publisher: Springer Science and Business Media LLC
Date: 31-10-2023
Measurement of the top-quark mass using a leptonic invariant mass in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 05-06-2023
Abstract: A measurement of the top-quark mass ( m t ) in the $$ t\\overline{t} $$ t t ¯ → lepton + jets channel is presented, with an experimental technique which exploits semileptonic decays of b -hadrons produced in the top-quark decay chain. The distribution of the invariant mass m ℓμ of the lepton, ℓ (with ℓ = e, μ ), from the W -boson decay and the muon, μ , originating from the b -hadron decay is reconstructed, and a binned-template profile likelihood fit is performed to extract m t . The measurement is based on data corresponding to an integrated luminosity of 36.1 fb − 1 of $$ \\sqrt{s} $$ s = 13 TeV pp collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. The measured value of the top-quark mass is m t = 174 . 41 ± 0 . 39 (stat.) ± 0 . 66 (syst.) ± 0 . 25 (recoil) GeV, where the third uncertainty arises from changing the P ythia 8 parton shower gluon-recoil scheme, used in top-quark decays, to a recently developed setup.
Measurement of the $$ t\overline{t} $$ production cross-section in pp collisions at $$ \sqrt{s} $$ = 5.02 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 23-06-2023
Abstract: The inclusive top-quark pair ( $$ t\\overline{t} $$ t t ¯ ) production cross-section $$ {\\sigma}_{t\\overline{t}} $$ σ t t ¯ is measured in proton–proton collisions at a centre-of-mass energy $$ \\sqrt{s} $$ s = 5 . 02 TeV, using 257 pb − 1 of data collected in 2017 by the ATLAS experiment at the LHC. The $$ t\\overline{t} $$ t t ¯ cross-section is measured in both the dilepton and single-lepton final states of the $$ t\\overline{t} $$ t t ¯ system and then combined. The combination of the two measurements yields $$ {\\sigma}_{t\\overline{t}}=67.5\\pm 0.9\\left(\\textrm{stat}.\\right)\\pm 2.3\\left(\\textrm{syst}.\\right)\\pm 1.1\\left(\\textrm{lumi}.\\right)\\pm 0.2\\left(\\textrm{beam}\\right)\\textrm{pb}, $$ σ t t ¯ = 67.5 ± 0.9 stat . ± 2.3 syst . ± 1.1 lumi . ± 0.2 beam pb , where the four uncertainties reflect the limited size of the data s le, experimental and theoretical systematic effects, and imperfect knowledge of both the integrated luminosity and the LHC beam energy, giving a total uncertainty of 3.9%. The result is in agreement with theoretical quantum chromodynamic calculations at next-to-next-to-leading order in the strong coupling constant, including the resummation of next-to-next-to-leading logarithmic soft-gluon terms, and constrains the parton distribution functions of the proton at large Bjorken- x .
Search for supersymmetry in final states with missing transverse momentum and three or more b-jets in 139 fb$$^{-1}$$ of proton–proton collisions at $$\sqrt{s} = 13$$ TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 04-07-2023
DOI: 10.1140/EPJC/S10052-023-11543-6
Abstract: A search for supersymmetry involving the pair production of gluinos decaying via off-shell third-generation squarks into the lightest neutralino $$(\\tilde{\\chi }^0_1)$$ ( χ ~ 1 0 ) is reported. It exploits LHC proton–proton collision data at a centre-of-mass energy $$\\sqrt{s} = 13$$ s = 13 TeV with an integrated luminosity of 139 fb $$^{-1}$$ - 1 collected with the ATLAS detector from 2015 to 2018. The search uses events containing large missing transverse momentum, up to one electron or muon, and several energetic jets, at least three of which must be identified as containing b -hadrons. Both a simple kinematic event selection and an event selection based upon a deep neural-network are used. No significant excess above the predicted background is found. In simplified models involving the pair production of gluinos that decay via off-shell top (bottom) squarks, gluino masses less than 2.44 TeV (2.35 TeV) are excluded at 95% CL for a massless $$\\tilde{\\chi }^0_1.$$ χ ~ 1 0 . Limits are also set on the gluino mass in models with variable branching ratios for gluino decays to $$b\\bar{b}\\tilde{\\chi }^0_1,$$ b b ¯ χ ~ 1 0 , $$t\\bar{t}\\tilde{\\chi }^0_1$$ t t ¯ χ ~ 1 0 and $$t\\bar{b}\\tilde{\\chi }^-_1/\\bar{t}b\\tilde{\\chi }^+_1.$$ t b ¯ χ ~ 1 - / t ¯ b χ ~ 1 + .
Search for heavy resonances decaying into a Z or W boson and a Higgs boson in final states with leptons and b-jets in 139 fb−1 of pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 05-06-2023
Abstract: This article presents a search for new resonances decaying into a Z or W boson and a 125 GeV Higgs boson h , and it targets the $$ \\nu \\overline{\\nu}b\\overline{b} $$ ν ν ¯ b b ¯ , $$ {\\ell}^{+}{\\ell}^{-}b\\overline{b} $$ ℓ + ℓ − b b ¯ , or $$ {\\ell}^{\\pm}\\nu b\\overline{b} $$ ℓ ± νb b ¯ final states, where ℓ = e or μ , in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV. The data used correspond to a total integrated luminosity of 139 fb − 1 collected by the ATLAS detector during Run 2 of the LHC at CERN. The search is conducted by examining the reconstructed invariant or transverse mass distributions of Zh or Wh candidates for evidence of a localised excess in the mass range from 220 GeV to 5 TeV. No significant excess is observed and 95% confidence-level upper limits between 1.3 pb and 0.3 fb are placed on the production cross section times branching fraction of neutral and charged spin-1 resonances and CP-odd scalar bosons. These limits are converted into constraints on the parameter space of the Heavy Vector Triplet model and the two-Higgs-doublet model.
Measurement of muon pairs produced via
γ γ
Publisher: American Physical Society (APS)
Date: 05-05-2023
Search for nonresonant pair production of Higgs bosons in the
b b
Publisher:
American Physical Society (APS)
Date:
05-09-2023
Publisher: American Physical Society (APS)
Date: 05-09-2023
Measurements of the suppression and correlations of dijets in Pb+Pb collisions at
s <
Publisher: American Physical Society (APS)
Date: 11-05-2023
Measurement of the c-jet mistagging efficiency in $$t\bar{t}$$ events using pp collision data at $$\sqrt{s}=13$$ $$\text {TeV}$$ collected with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 2022
DOI: 10.1140/EPJC/S10052-021-09843-W
Abstract: A technique is presented to measure the efficiency with which c -jets are mistagged as b -jets (mistagging efficiency) using $$t\\bar{t}$$ t t ¯ events, where one of the W bosons decays into an electron or muon and a neutrino and the other decays into a quark–antiquark pair. The measurement utilises the relatively large and known $$W\\rightarrow cs$$ W → c s branching ratio, which allows a measurement to be made in an inclusive c -jet s le. The data s le used was collected by the ATLAS detector at $$\\sqrt{s} = 13$$ s = 13 $$\\text {TeV}$$ TeV and corresponds to an integrated luminosity of 139 fb $$^{-1}$$ - 1 . Events are reconstructed using a kinematic likelihood technique which selects the mapping between jets and $$t\\bar{t}$$ t t ¯ decay products that yields the highest likelihood value. The distribution of the b -tagging discriminant for jets from the hadronic W decays in data is compared with that in simulation to extract the mistagging efficiency as a function of jet transverse momentum. The total uncertainties are in the range 3–17%. The measurements generally agree with those in simulation but there are some differences in the region corresponding to the most stringent b -jet tagging requirement.
Searches for new phenomena in events with two leptons, jets, and missing transverse momentum in 139 fb$$^{-1}$$ of $$\varvec{\sqrt{s}}=13$$ TeV $$\varvec{pp}$$ collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 19-06-2023
DOI: 10.1140/EPJC/S10052-023-11434-W
Abstract: Searches for new phenomena inspired by supersymmetry in final states containing an $$e^+e^-$$ e + e - or $$\\mu ^+\\mu ^-$$ μ + μ - pair, jets, and missing transverse momentum are presented. These searches make use of proton–proton collision data with an integrated luminosity of $$139~\\text {fb}^{-1}$$ 139 fb - 1 , collected during 2015–2018 at a centre-of-mass energy $$\\sqrt{s}=13~$$ s = 13 TeV by the ATLAS detector at the Large Hadron Collider. Two searches target the pair production of charginos and neutralinos. One uses the recursive-jigsaw reconstruction technique to follow up on excesses observed in $$36.1~\\text {fb}^{-1}$$ 36.1 fb - 1 of data, and the other uses conventional event variables. The third search targets pair production of coloured supersymmetric particles (squarks or gluinos) decaying through the next-to-lightest neutralino $$(\\tilde{\\chi }_2^0)$$ ( χ ~ 2 0 ) via a slepton $$(\\tilde{\\ell })$$ ( ℓ ~ ) or Z boson into $$\\ell ^+\\ell ^-\\tilde{\\chi }_1^0$$ ℓ + ℓ - χ ~ 1 0 , resulting in a kinematic endpoint or peak in the dilepton invariant mass spectrum. The data are found to be consistent with the Standard Model expectations. Results are interpreted using simplified models and exclude masses up to 900 GeV for electroweakinos, 1550 GeV for squarks, and 2250 GeV for gluinos.
Calibration of the light-flavour jet mistagging efficiency of the b-tagging algorithms with Z+jets events using 139 $$\textrm{fb}^{-1}$$ of ATLAS proton–proton collision data at $$\sqrt{s} = 13$$ TeV
Publisher: Springer Science and Business Media LLC
Date: 14-08-2023
DOI: 10.1140/EPJC/S10052-023-11736-Z
Abstract: The identification of b -jets, referred to as b -tagging, is an important part of many physics analyses in the ATLAS experiment at the Large Hadron Collider and an accurate calibration of its performance is essential for high-quality physics results. This publication describes the calibration of the light-flavour jet mistagging efficiency in a data s le of proton–proton collision events at $$\\sqrt{s}=13$$ s = 13 TeV corresponding to an integrated luminosity of 139 fb $$^{-1}$$ - 1 . The calibration is performed in a s le of Z bosons produced in association with jets. Due to the low mistagging efficiency for light-flavour jets, a method which uses modified versions of the b -tagging algorithms referred to as flip taggers is used in this work. A fit to the jet-flavour-sensitive secondary-vertex mass is performed to extract a scale factor from data, to correct the light-flavour jet mistagging efficiency in Monte Carlo simulations, while simultaneously correcting the b -jet efficiency. With this procedure, uncertainties coming from the modeling of jets from heavy-flavour hadrons are considerably lower than in previous calibrations of the mistagging scale factors, where they were dominant. The scale factors obtained in this calibration are consistent with unity within uncertainties.
Search for single production of vector-like T quarks decaying into Ht or Zt in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 23-08-2023
Abstract: This paper describes a search for the single production of an up-type vector-like quark ( T ) decaying as T → Ht or T → Zt . The search utilises a dataset of pp collisions at $$ \\sqrt{s} $$ s = 13 TeV collected with the ATLAS detector during the 2015–2018 data-taking period of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb − 1 . Data are analysed in final states containing a single lepton with multiple jets and b -jets. The presence of boosted heavy resonances in the event is exploited to discriminate the signal from the Standard Model background. No significant excess above the Standard Model expectation is observed, and 95% CL upper limits are set on the production cross section of T quarks in different decay channels. The results are interpreted in several benchmark scenarios to set limits on the mass and universal coupling strength ( κ ) of the vector-like quark. For singlet T quarks, κ values above 0.53 are excluded for all masses below 2.3 TeV. At a mass of 1.6 TeV, κ values as low as 0.35 are excluded. For T quarks in the doublet scenario, where the production cross section is much lower, κ values above 0.72 are excluded for all masses below 1.7 TeV, and this exclusion is extended to κ above 0.55 for low masses around 1.0 TeV.
Search for dark matter in events with missing transverse momentum and a Higgs boson decaying into two photons in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 10-2021
Abstract: A search for dark-matter particles in events with large missing transverse momentum and a Higgs boson candidate decaying into two photons is reported. The search uses 139 fb − 1 of proton-proton collision data collected at $$ \\sqrt{s} $$ s = 13 TeV with the ATLAS detector at the CERN LHC between 2015 and 2018. No significant excess of events over the Standard Model predictions is observed. The results are interpreted by extracting limits on three simplified models that include either vector or pseudoscalar mediators and predict a final state with a pair of dark-matter candidates and a Higgs boson decaying into two photons.
Search for new phenomena with top quark pairs in final states with one lepton, jets, and missing transverse momentum in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 19-04-2021
Abstract: A search for new phenomena with top quark pairs in final states with one isolated electron or muon, multiple jets, and large missing transverse momentum is performed. Signal regions are designed to search for two-, three-, and four-body decays of the directly pair-produced supersymmetric partner of the top quark (stop). Additional signal regions are designed specifically to search for spin-0 mediators that are produced in association with a pair of top quarks and decay into a pair of dark-matter particles. The search is performed using the Large Hadron Collider proton-proton collision dataset at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV recorded by the ATLAS detector from 2015 to 2018, corresponding to an integrated luminosity of 139 fb − 1 . No significant excess above the Standard Model background is observed, and limits at 95% confidence level are set in the stop-neutralino mass plane and as a function of the mediator mass or the dark-matter particle mass. Stops are excluded up to 1200 GeV (710 GeV) in the two-body (three-body) decay scenario. In the four-body scenario stops up to 640 GeV are excluded for a stop-neutralino mass difference of 60 GeV. Scalar and pseudoscalar dark-matter mediators are excluded up to 200 GeV when the coupling strengths of the mediator to Standard Model and dark-matter particles are both equal to one and when the mass of the dark-matter particle is 1 GeV.
Search for Higgs boson pair production in the two bottom quarks plus two photons final state in
p p
Publisher:
American Physical Society (APS)
Date:
06-09-2022
Publisher: American Physical Society (APS)
Date: 06-09-2022
Search for dijet resonances in events with an isolated charged lepton using $$ \sqrt{s} $$ = 13 TeV proton-proton collision data collected by the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 06-2020
Search for squarks and gluinos in final states with jets and missing transverse momentum using 139 fb−1 of $$ \sqrt{s} $$ = 13 TeV pp collision data with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 02-2021
Abstract: A search for the supersymmetric partners of quarks and gluons (squarks and gluinos) in final states containing jets and missing transverse momentum, but no electrons or muons, is presented. The data used in this search were recorded by the ATLAS experiment in proton-proton collisions at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb − 1 . The results are interpreted in the context of various R -parity-conserving models where squarks and gluinos are produced in pairs or in association and a neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 2.30 TeV for a simplified model containing only a gluino and the lightest neutralino, assuming the latter is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.85 TeV are excluded if the lightest neutralino is massless. These limits extend substantially beyond the region of supersymmetric parameter space excluded previously by similar searches with the ATLAS detector.
Search for doubly charged Higgs boson production in multi-lepton final states using 139 fb$$^{-1}$$ of proton–proton collisions at $$\sqrt{s}$$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 12-07-2023
DOI: 10.1140/EPJC/S10052-023-11578-9
Abstract: A search for pair production of doubly charged Higgs bosons ( $$H^{\\pm \\pm }$$ H ± ± ), each decaying into a pair of prompt, isolated, and highly energetic leptons with the same electric charge, is presented. The search uses a proton–proton collision data s le at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb $$^{-1}$$ - 1 recorded by the ATLAS detector during Run 2 of the Large Hadron Collider (LHC). This analysis focuses on same-charge leptonic decays, $$H^{\\pm \\pm } \\!\\rightarrow \\ell ^{\\pm } \\ell ^{\\prime \\pm }$$ H ± ± → ℓ ± ℓ ′ ± where $$\\ell , \\ell ^\\prime \\!=\\!e, \\mu , \\tau $$ ℓ , ℓ ′ = e , μ , τ , in two-, three-, and four-lepton channels, but only considers final states which include electrons or muons. No evidence of a signal is observed. Corresponding upper limits on the production cross-section of a doubly charged Higgs boson are derived, as a function of its mass $$m(H^{\\pm \\pm })$$ m ( H ± ± ) , at 95% confidence level. Assuming that the branching ratios to each of the possible leptonic final states are equal, $$\\mathcal {B}(H^{\\pm \\pm } \\rightarrow e^\\pm e^\\pm ) = \\mathcal {B}(H^{\\pm \\pm } \\rightarrow e^\\pm \\mu ^\\pm ) = \\mathcal {B}(H^{\\pm \\pm } \\rightarrow \\mu ^\\pm \\mu ^\\pm ) = \\mathcal {B}(H^{\\pm \\pm } \\rightarrow e^\\pm \\tau ^\\pm ) = \\mathcal {B}(H^{\\pm \\pm } \\rightarrow \\mu ^\\pm \\tau ^\\pm ) = \\mathcal {B}(H^{\\pm \\pm } \\rightarrow \\tau ^\\pm \\tau ^\\pm ) = 1/6$$ B ( H ± ± → e ± e ± ) = B ( H ± ± → e ± μ ± ) = B ( H ± ± → μ ± μ ± ) = B ( H ± ± → e ± τ ± ) = B ( H ± ± → μ ± τ ± ) = B ( H ± ± → τ ± τ ± ) = 1 / 6 , the observed (expected) lower limit on the mass of a doubly charged Higgs boson is 1080 GeV (1065 GeV) within the left-right symmetric type-II seesaw model, which is the strongest limit to date produced by the ATLAS Collaboration. Additionally, this paper provides the first direct test of the Zee–Babu neutrino mass model at the LHC, yielding an observed (expected) lower limit of $$m(H^{\\pm \\pm })$$ m ( H ± ± ) = 900 GeV (880 GeV).
Performance of the ATLAS muon triggers in Run 2
Publisher: IOP Publishing
Date: 14-09-2020
Search for dark matter produced in association with a single top quark and an energetic W boson in $$\sqrt{s}=$$ 13 TeV $$pp$$ collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 12-07-2023
DOI: 10.1140/EPJC/S10052-023-11582-Z
Abstract: This paper presents a search for dark matter, $$\\chi $$ χ , using events with a single top quark and an energetic W boson. The analysis is based on proton–proton collision data collected with the ATLAS experiment at $$\\sqrt{s}=$$ s = 13 TeV during LHC Run 2 (2015–2018), corresponding to an integrated luminosity of 139 fb $$^{-1}$$ - 1 . The search considers final states with zero or one charged lepton (electron or muon), at least one b -jet and large missing transverse momentum. In addition, a result from a previous search considering two-charged-lepton final states is included in the interpretation of the results. The data are found to be in good agreement with the Standard Model predictions and the results are interpreted in terms of 95% confidence-level exclusion limits in the context of a class of dark matter models involving an extended two-Higgs-doublet sector together with a pseudoscalar mediator particle. The search is particularly sensitive to on-shell production of the charged Higgs boson state, $$H^{\\pm }$$ H ± , arising from the two-Higgs-doublet mixing, and its semi-invisible decays via the mediator particle, a : $$H^{\\pm } \\rightarrow W^\\pm a (\\rightarrow \\chi \\chi )$$ H ± → W ± a ( → χ χ ) . Signal models with $$H^{\\pm }$$ H ± masses up to 1.5 TeV and a masses up to 350 GeV are excluded assuming a $$\\tan \\beta $$ tan β value of 1. For masses of a of 150 (250) GeV, $$\\tan \\beta $$ tan β values up to 2 are excluded for $$H^{\\pm }$$ H ± masses between 200 (400) GeV and 1.5 TeV. Signals with $$\\tan \\beta $$ tan β values between 20 and 30 are excluded for $$H^{\\pm }$$ H ± masses between 500 and 800 GeV.
Performance of the missing transverse momentum triggers for the ATLAS detector during Run-2 data taking
Publisher: Springer Science and Business Media LLC
Date: 08-2020
Abstract: The factor of four increase in the LHC luminosity, from 0 . 5 × 10 34 cm − 2 s − 1 to 2 . 0 × 10 34 cm − 2 s − 1 , and the corresponding increase in pile-up collisions during the 2015–2018 data-taking period, presented a challenge for the ATLAS trigger, particularly for those algorithms that select events with missing transverse momentum. The output data rate at fixed threshold typically increases exponentially with the number of pile-up collisions, so the legacy algorithms from previous LHC data-taking periods had to be tuned and new approaches developed to maintain the high trigger efficiency achieved in earlier operations. A study of the trigger performance and comparisons with simulations show that these changes resulted in event selection efficiencies of 98% for this period, meeting and in some cases exceeding the performance of similar triggers in earlier run periods, while at the same time keeping the necessary bandwidth within acceptable limits.
Search for invisible Higgs-boson decays in events with vector-boson fusion signatures using 139 fb−1 of proton-proton data recorded by the ATLAS experiment
Publisher: Springer Science and Business Media LLC
Date: 08-08-2022
Abstract: A direct search for Higgs bosons produced via vector-boson fusion and subsequently decaying into invisible particles is reported. The analysis uses 139 fb − 1 of pp collision data at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV recorded by the ATLAS detector at the LHC. The observed numbers of events are found to be in agreement with the background expectation from Standard Model processes. For a scalar Higgs boson with a mass of 125 GeV and a Standard Model production cross section, an observed upper limit of 0 . 145 is placed on the branching fraction of its decay into invisible particles at 95% confidence level, with an expected limit of 0 . 103. These results are interpreted in the context of models where the Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross section of weakly interacting massive particles and nucleons. Invisible decays of additional scalar bosons with masses from 50 GeV to 2 TeV are also studied, and the derived upper limits on the cross section times branching fraction decrease with increasing mass from 1 . 0 pb for a scalar boson mass of 50 GeV to 0 . 1 pb at a mass of 2 TeV.
Search for the HH → $$ b\overline{b}b\overline{b} $$ process via vector-boson fusion production using proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 07-2020
Abstract: A search for Higgs boson pair production via vector-boson fusion (VBF) in the $$ b\\overline{b}b\\overline{b} $$ b b ¯ b b ¯ final state is carried out with the ATLAS experiment using 126 fb − 1 of proton- proton collision data delivered at $$ \\sqrt{s} $$ s = 13 TeV by the Large Hadron Collider. This search is sensitive to VBF production of additional heavy bosons that may decay into Higgs boson pairs, and in a non-resonant topology it can constrain the quartic coupling between the Higgs bosons and vector bosons. No significant excess relative to the Standard Model expectation is observed, and limits on the production cross-section are set at the 95% confidence level for a heavy scalar resonance in the context of an extended Higgs sector, and for non-resonant Higgs boson pair production. Interpretation in terms of the coupling between a Higgs boson pair and two vector bosons is also provided: coupling values normalised to the Standard Model expectation of κ 2 V − 0 . 76 and κ 2 V 2 . 90 are excluded at the 95% confidence level in data.
A search for the dimuon decay of the Standard Model Higgs boson with the ATLAS detector
Publisher: Elsevier BV
Date: 2021
Evidence for Higgs boson decays to a low-mass dilepton system and a photon in pp collisions at s<
Publisher: Elsevier BV
Date: 08-2021
Constraints on the Higgs boson self-coupling from single- and double-Higgs production with the ATLAS detector using pp collisions at
Publisher:
Elsevier BV
Date:
08-2023
Publisher: Elsevier BV
Date: 08-2023
Search for dark matter produced in association with a Standard Model Higgs boson decaying into b-quarks using the full Run 2 dataset from the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 11-2021
Abstract: The production of dark matter in association with Higgs bosons is predicted in several extensions of the Standard Model. An exploration of such scenarios is presented, considering final states with missing transverse momentum and b -tagged jets consistent with a Higgs boson. The analysis uses proton-proton collision data at a centre-of-mass energy of 13 TeV recorded by the ATLAS experiment at the LHC during Run 2, amounting to an integrated luminosity of 139 fb − 1 . The analysis, when compared with previous searches, benefits from a larger dataset, but also has further improvements providing sensitivity to a wider spectrum of signal scenarios. These improvements include both an optimised event selection and advances in the object identification, such as the use of the likelihood-based significance of the missing transverse momentum and variable-radius track-jets. No significant deviation from Standard Model expectations is observed. Limits are set, at 95% confidence level, in two benchmark models with two Higgs doublets extended by either a heavy vector boson Z ′ or a pseudoscalar singlet a and which both provide a dark matter candidate χ . In the case of the two-Higgs-doublet model with an additional vector boson Z ′, the observed limits extend up to a Z ′ mass of 3 TeV for a mass of 100 GeV for the dark matter candidate. The two-Higgs-doublet model with a dark matter particle mass of 10 GeV and an additional pseudoscalar a is excluded for masses of the a up to 520 GeV and 240 GeV for tan β = 1 and tan β = 10 respectively. Limits on the visible cross-sections are set and range from to 0.05 fb to 3.26 fb, depending on the missing transverse momentum and b -quark jet multiplicity requirements.
Search for resonances decaying into photon pairs in 139 fb−1 of pp collisions at s
Publisher:
Elsevier BV
Date:
11-2021
Publisher: Elsevier BV
Date: 11-2021
Production of
Υ ( n S )
Publisher:
American Physical Society (APS)
Date:
22-05-2023
Publisher: American Physical Society (APS)
Date: 22-05-2023
Comparison of inclusive and photon-tagged jet suppression in 5.02 TeV Pb+Pb collisions with ATLAS
Publisher: Elsevier BV
Date: 11-2023
Search for new phenomena in events with two opposite-charge leptons, jets and missing transverse momentum in pp collisions at $$ \sqrt{\mathrm{s}} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 04-2021
Abstract: The results of a search for direct pair production of top squarks and for dark matter in events with two opposite-charge leptons (electrons or muons), jets and missing transverse momentum are reported, using 139 fb − 1 of integrated luminosity from proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV, collected by the ATLAS detector at the Large Hadron Collider during Run 2 (2015–2018). This search considers the pair production of top squarks and is sensitive across a wide range of mass differences between the top squark and the lightest neutralino. Additionally, spin-0 mediator dark-matter models are considered, in which the mediator is produced in association with a pair of top quarks. The mediator subsequently decays to a pair of dark-matter particles. No significant excess of events is observed above the Standard Model background, and limits are set at 95% confidence level. The results exclude top squark masses up to about 1 TeV, and masses of the lightest neutralino up to about 500 GeV. Limits on dark-matter production are set for scalar (pseudoscalar) mediator masses up to about 250 (300) GeV.
Measurements of Higgs bosons decaying to bottom quarks from vector boson fusion production with the ATLAS experiment at $$\sqrt{s}=13\,\text {TeV}$$
Publisher: Springer Science and Business Media LLC
Date: 06-2021
DOI: 10.1140/EPJC/S10052-021-09192-8
Abstract: The paper presents a measurement of the Standard Model Higgs Boson decaying to b -quark pairs in the vector boson fusion (VBF) production mode. A s le corresponding to 126 $$\\hbox {fb}^{-1}$$ fb - 1 of $$\\sqrt{s} = 13\\,\\text {TeV}$$ s = 13 TeV proton–proton collision data, collected with the ATLAS experiment at the Large Hadron Collider, is analyzed utilizing an adversarial neural network for event classification. The signal strength, defined as the ratio of the measured signal yield to that predicted by the Standard Model for VBF Higgs production, is measured to be $$0.95^{+0.38}_{-0.36}$$ 0 . 95 - 0.36 + 0.38 , corresponding to an observed (expected) significance of 2.6 (2.8) standard deviations from the background only hypothesis. The results are additionally combined with an analysis of Higgs bosons decaying to b -quarks, produced via VBF in association with a photon.
Search for flavour-changing neutral current interactions of the top quark and the Higgs boson in events with a pair of τ-leptons in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 23-06-2023
Abstract: A search for flavour-changing neutral current (FCNC) tqH interactions involving a top quark, another up-type quark ( q = u, c ), and a Standard Model (SM) Higgs boson decaying into a τ -lepton pair ( H → τ + τ − ) is presented. The search is based on a dataset of pp collisions at $$ \\sqrt{s} $$ s = 13 TeV that corresponds to an integrated luminosity of 139 fb − 1 recorded with the ATLAS detector at the Large Hadron Collider. Two processes are considered: single top quark FCNC production in association with a Higgs boson ( pp → tH ), and top quark pair production in which one of top quarks decays into Wb and the other decays into qH through the FCNC interactions. The search selects events with two hadronically decaying τ -lepton candidates ( τ had ) or at least one τ had with an additional lepton ( e , μ ), as well as multiple jets. Event kinematics is used to separate signal from the background through a multivariate discriminant. A slight excess of data is observed with a significance of 2.3 σ above the expected SM background, and 95% CL upper limits on the t → qH branching ratios are derived. The observed (expected) 95% CL upper limits set on the t → cH and t → uH branching ratios are $$ 9.4\\times {10}^{-4}\\left({4.8}_{-1.4}^{+2.2}\\times {10}^{-4}\\right) $$ 9.4 × 10 − 4 4.8 − 1.4 + 2.2 × 10 − 4 and $$ 6.9\\times {10}^{-4}\\left({3.5}_{-1.0}^{+1.5}\\times {10}^{-4}\\right) $$ 6.9 × 10 − 4 3.5 − 1.0 + 1.5 × 10 − 4 , respectively. The corresponding combined observed (expected) upper limits on the dimension-6 operator Wilson coefficients in the effective tqH couplings are C cϕ 1 . 35 (0 . 97) and C uϕ 1 . 16 (0 . 82).
Search for light long-lived neutral particles that decay to collimated pairs of leptons or light hadrons in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 23-06-2023
Abstract: A search for light long-lived neutral particles with masses in the O (MeV–GeV) range is presented. The analysis targets the production of long-lived dark photons in the decay of a Higgs boson produced via gluon–gluon fusion or in association with a W boson. Events that contain displaced collimated Standard Model fermions reconstructed in the calorimeter or muon spectrometer are selected in 139 fb − 1 of $$ \\sqrt{s} $$ s = 13 TeV pp collision data collected by the ATLAS detector at the LHC. Background estimates for contributions from Standard Model processes and instrumental effects are extracted from data. The observed event yields are consistent with the expected background. Exclusion limits are reported on the production cross-section times branching fraction as a function of the mean proper decay length cτ of the dark photon, or as a function of the dark-photon mass and kinetic mixing parameter that quantifies the coupling between the Standard Model and potential hidden (dark) sectors. A Higgs boson branching fraction above 1% is excluded at 95% CL for a Higgs boson decaying into two dark photons for dark-photon mean proper decay lengths between 10 mm and 250 mm and dark photons with masses between 0.4 GeV and 2 GeV.
Search for direct pair production of sleptons and charginos decaying to two leptons and neutralinos with mass splittings near the W-boson mass in $$ \sqrt{s} $$ = 13 TeV pp collisions with the ATLAS d
Publisher: Springer Science and Business Media LLC
Date: 06-06-2023
Abstract: A search for the electroweak production of pairs of charged sleptons or charginos decaying into two-lepton final states with missing transverse momentum is presented. Two simplified models of R -parity-conserving supersymmetry are considered: direct pair-production of sleptons $$ \\left(\\overset{\\sim }{\\ell}\\overset{\\sim }{\\ell}\\right) $$ ℓ ~ ℓ ~ , with each decaying into a charged lepton and a $$ {\\overset{\\sim }{\\chi}}_1^0 $$ χ ~ 1 0 neutralino, and direct pair-production of the lightest charginos $$ \\left({\\overset{\\sim }{\\chi}}_1^{\\pm }{\\overset{\\sim }{\\chi}}_1^{\\mp}\\right) $$ χ ~ 1 ± χ ~ 1 ∓ , with each decaying into a W -boson and a $$ {\\overset{\\sim }{\\chi}}_1^0 $$ χ ~ 1 0 . The lightest neutralino $$ \\left({\\overset{\\sim }{\\chi}}_1^0\\right) $$ χ ~ 1 0 is assumed to be the lightest supersymmetric particle (LSP). The analyses target the experimentally challenging mass regions where $$ m\\left(\\overset{\\sim }{\\ell}\\right)-m\\left({\\overset{\\sim }{\\chi}}_1^0\\right) $$ m ℓ ~ − m χ ~ 1 0 and $$ m\\left({\\overset{\\sim }{\\chi}}_1^{\\pm}\\right)-m\\left({\\overset{\\sim }{\\chi}}_1^0\\right) $$ m χ ~ 1 ± − m χ ~ 1 0 are close to the W -boson mass (‘moderately compressed’ regions). The search uses 139 fb − 1 of $$ \\sqrt{s} $$ s = 13 TeV proton-proton collisions recorded by the ATLAS detector at the Large Hadron Collider. No significant excesses over the expected background are observed. Exclusion limits on the simplified models under study are reported in the $$ \\left(\\overset{\\sim }{\\ell },{\\overset{\\sim }{\\chi}}_1^0\\right) $$ ℓ ~ χ ~ 1 0 and $$ \\left({\\overset{\\sim }{\\chi}}_1^{\\pm }{\\overset{\\sim }{\\chi}}_1^0\\right) $$ χ ~ 1 ± χ ~ 1 0 mass planes at 95% confidence level (CL). Sleptons with masses up to 150 GeV are excluded at 95% CL for the case of a mass-splitting between sleptons and the LSP of 50 GeV. Chargino masses up to 140 GeV are excluded at 95% CL for the case of a mass-splitting between the chargino and the LSP down to about 100 GeV.
Search for a new Z′ gauge boson in 4μ events with the ATLAS experiment
Publisher: Springer Science and Business Media LLC
Date: 12-07-2023
Abstract: This paper presents a search for a new Z ′ vector gauge boson with the ATLAS experiment at the Large Hadron Collider using pp collision data collected at $$ \\sqrt{s} $$ s = 13 TeV, corresponding to an integrated luminosity of 139 fb − 1 . The new gauge boson Z ′ is predicted by L μ − L τ models to address observed phenomena that can not be explained by the Standard Model. The search examines the four-muon (4 μ ) final state, using a deep learning neural network classifier to separate the Z ′ signal from the Standard Model background events. The di-muon invariant masses in the 4 μ events are used to extract the Z ′ resonance signature. No significant excess of events is observed over the predicted background. Upper limits at a 95% confidence level on the Z ′ production cross-section times the decay branching fraction of pp → Z ′ μμ → 4 μ are set from 0.31 to 4.3 fb for the Z ′ mass ranging from 5 to 81 GeV. The corresponding common coupling strengths, g Z ′ , of the Z ′ boson to the second and third generation leptons above 0.003 – 0.2 have been excluded.
Measurement of exclusive pion pair production in proton–proton collisions at $$\sqrt{s}={7}\,\text {TeV}$$ with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 17-07-2023
DOI: 10.1140/EPJC/S10052-023-11700-X
Abstract: The exclusive production of pion pairs in the process $$pp\\rightarrow pp\\pi ^+\\pi ^-$$ p p → p p π + π - has been measured at $$\\sqrt{s}={7}\\,\\text {TeV}$$ s = 7 TeV with the ATLAS detector at the LHC, using $${80}\\,{\\upmu \\textrm{b}}^{-1}$$ 80 μ b - 1 of low-luminosity data. The pion pairs were detected in the ATLAS central detector while outgoing protons were measured in the forward ATLAS ALFA detector system. This represents the first use of proton tagging to measure an exclusive hadronic final state at the LHC. A cross-section measurement is performed in two kinematic regions defined by the proton momenta, the pion rapidities and transverse momenta, and the pion–pion invariant mass. Cross-section values of $$4.8 \\pm 1.0 \\mathrm {\\ (stat)} {~}^{+0.3}_{-0.2} \\mathrm {\\ (syst)}\\ {\\upmu \\textrm{b}}$$ 4.8 ± 1.0 ( stat ) - 0.2 + 0.3 ( syst ) μ b and $$9 \\pm 6 \\mathrm {\\ (stat)} {~}^{+2}_{-2} \\mathrm {\\ (syst)}\\ {\\upmu \\textrm{b}} $$ 9 ± 6 ( stat ) - 2 + 2 ( syst ) μ b are obtained in the two regions they are compared with theoretical models and provide a demonstration of the feasibility of measurements of this type.
Measurement of the charge asymmetry in top-quark pair production in association with a photon with the ATLAS experiment
Publisher: Elsevier BV
Date: 08-2023
Search for heavy, long-lived, charged particles with large ionisation energy loss in pp collisions at $$ \sqrt{s} $$ = 13 TeV using the ATLAS experiment and the full Run 2 dataset
Publisher: Springer Science and Business Media LLC
Date: 26-06-2023
Abstract: This paper presents a search for hypothetical massive, charged, long-lived particles with the ATLAS detector at the LHC using an integrated luminosity of 139 fb − 1 of proton–proton collisions at $$ \\sqrt{s} $$ s = 13 TeV. These particles are expected to move significantly slower than the speed of light and should be identifiable by their high transverse momenta and anomalously large specific ionisation losses, d E/ d x . Trajectories reconstructed solely by the inner tracking system and a d E/ d x measurement in the pixel detector layers provide sensitivity to particles with lifetimes down to $$ \\mathcal{O} $$ O (1) ns with a mass, measured using the Bethe–Bloch relation, ranging from 100 GeV to 3 TeV. Interpretations for pair-production of R -hadrons, charginos and staus in scenarios of supersymmetry compatible with these particles being long-lived are presented, with mass limits extending considerably beyond those from previous searches in broad ranges of lifetime.
A search for new resonances in multiple final states with a high transverse momentum Z boson in $$ \sqrt{s} $$ = 13 TeV pp collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 07-06-2023
Abstract: A generic search for resonances is performed with events containing a Z boson with transverse momentum greater than 100 GeV, decaying into e + e − or μ + μ − . The analysed data collected with the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider correspond to an integrated luminosity of 139 fb − 1 . Two invariant mass distributions are examined for a localised excess relative to the expected Standard Model background in six independent event categories (and their inclusive sum) to increase the sensitivity. No significant excess is observed. Exclusion limits at 95% confidence level are derived for two cases: a model-independent interpretation of Gaussian-shaped resonances with the mass width between 3% and 10% of the resonance mass, and a specific heavy vector triplet model with the decay mode W ′ → ZW → ℓℓqq .
Determination of the strong coupling constant from transverse energy-energy correlations in multijet events at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 11-07-2023
Abstract: Measurements of transverse energy-energy correlations and their associated azimuthal asymmetries in multijet events are presented. The analysis is performed using a data s le corresponding to 139 fb − 1 of proton-proton collisions at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV, collected with the ATLAS detector at the Large Hadron Collider. The measurements are presented in bins of the scalar sum of the transverse momenta of the two leading jets and unfolded to particle level. They are then compared to next-to-next-to-leading-order perturbative QCD calculations for the first time, which feature a significant reduction in the theoretical uncertainties estimated using variations of the renormalisation and factorisation scales. The agreement between data and theory is good, thus providing a precision test of QCD at large momentum transfers Q . The strong coupling constant α s is extracted as a function of Q , showing a good agreement with the renormalisation group equation and with previous analyses. A simultaneous fit to all transverse energy-energy correlation distributions across different kinematic regions yields a value of $$ {\\alpha}_{\\textrm{s}}\\left({m}_Z\\right)=0.1175\\pm 0.0006{\\left(\\exp .\\right)}_{-0.0017}^{+0.0034}\\left(\\textrm{theo}.\\right) $$ α s m Z = 0.1175 ± 0.0006 exp . − 0.0017 + 0.0034 theo . , while the global fit to the asymmetry distributions yields $$ {\\alpha}_{\\textrm{s}}\\left({m}_Z\\right)=0.1185\\pm 0.0009{\\left(\\exp .\\right)}_{-0.0012}^{+0.0025}\\left(\\textrm{theo}.\\right) $$ α s m Z = 0.1185 ± 0.0009 exp . − 0.0012 + 0.0025 theo . .
Measurement of the associated production of a Higgs boson decaying into b-quarks with a vector boson at high transverse momentum in pp collisions at
Publisher:
Elsevier BV
Date:
05-2021
Publisher: Elsevier BV
Date: 05-2021
Inclusive-photon production and its dependence on photon isolation in pp collisions at $$ \sqrt{s} $$ = 13 TeV using 139 fb−1 of ATLAS data
Publisher: Springer Science and Business Media LLC
Date: 11-07-2023
Abstract: Measurements of differential cross sections are presented for inclusive isolated-photon production in pp collisions at a centre-of-mass energy of 13 TeV provided by the LHC and using 139 fb − 1 of data recorded by the ATLAS experiment. The cross sections are measured as functions of the photon transverse energy in different regions of photon pseudorapidity. The photons are required to be isolated by means of a fixed-cone method with two different cone radii. The dependence of the inclusive-photon production on the photon isolation is investigated by measuring the fiducial cross sections as functions of the isolation-cone radius and the ratios of the differential cross sections with different radii in different regions of photon pseudorapidity. The results presented in this paper constitute an improvement with respect to those published by ATLAS earlier: the measurements are provided for different isolation radii and with a more granular segmentation in photon pseudorapidity that can be exploited in improving the determination of the proton parton distribution functions. These improvements provide a more in-depth test of the theoretical predictions. Next-to-leading-order QCD predictions from JETPHOX and SHERPA and next-to-next-to-leading-order QCD predictions from NNLOJET are compared to the measurements, using several parameterisations of the proton parton distribution functions. The measured cross sections are well described by the fixed-order QCD predictions within the experimental and theoretical uncertainties in most of the investigated phase-space region.
Reconstruction and identification of boosted di-τ systems in a search for Higgs boson pairs using 13 TeV proton-proton collision data in ATLAS
Publisher: Springer Science and Business Media LLC
Date: 11-2020
Abstract: In this paper, a new technique for reconstructing and identifying hadronically decaying τ + τ − pairs with a large Lorentz boost, referred to as the di- τ tagger, is developed and used for the first time in the ATLAS experiment at the Large Hadron Collider. A benchmark di- τ tagging selection is employed in the search for resonant Higgs boson pair production, where one Higgs boson decays into a boosted $$ b\\overline{b} $$ b b ¯ pair and the other into a boosted τ + τ − pair, with two hadronically decaying τ -leptons in the final state. Using 139 fb − 1 of proton-proton collision data recorded at a centre-of-mass energy of 13 TeV, the efficiency of the di- τ tagger is determined and the background with quark- or gluon-initiated jets misidentified as di- τ objects is estimated. The search for a heavy, narrow, scalar resonance produced via gluon-gluon fusion and decaying into two Higgs bosons is carried out in the mass range 1–3 TeV using the same dataset. No deviations from the Standard Model predictions are observed, and 95% confidence-level exclusion limits are set on this model.
Measurement of the properties of Higgs boson production at $$ \sqrt{s} $$ = 13 TeV in the H → γγ channel using 139 fb−1 of pp collision data with the ATLAS experiment
Publisher: Springer Science and Business Media LLC
Date: 11-07-2023
Abstract: Measurements of Higgs boson production cross-sections are carried out in the diphoton decay channel using 139 fb − 1 of pp collision data at $$ \\sqrt{s} $$ s = 13 TeV collected by the ATLAS experiment at the LHC. The analysis is based on the definition of 101 distinct signal regions using machine-learning techniques. The inclusive Higgs boson signal strength in the diphoton channel is measured to be $$ {1.04}_{-0.09}^{+0.10} $$ 1.04 − 0.09 + 0.10 . Cross-sections for gluon-gluon fusion, vector-boson fusion, associated production with a W or Z boson, and top associated production processes are reported. An upper limit of 10 times the Standard Model prediction is set for the associated production process of a Higgs boson with a single top quark, which has a unique sensitivity to the sign of the top quark Yukawa coupling. Higgs boson production is further characterized through measurements of Simplified Template Cross-Sections (STXS). In total, cross-sections of 28 STXS regions are measured. The measured STXS cross-sections are compatible with their Standard Model predictions, with a p -value of 93%. The measurements are also used to set constraints on Higgs boson coupling strengths, as well as on new interactions beyond the Standard Model in an effective field theory approach. No significant deviations from the Standard Model predictions are observed in these measurements, which provide significant sensitivity improvements compared to the previous ATLAS results.
Search for flavour-changing neutral-current couplings between the top quark and the photon with the ATLAS detector at
Publisher:
Elsevier BV
Date:
07-2023
Publisher: Elsevier BV
Date: 07-2023
Search for lepton-flavour violation in high-mass dilepton final states using 139 fb−1 of pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 13-10-2023
A detailed map of Higgs boson interactions by the ATLAS experiment ten years after the discovery
Publisher: Springer Science and Business Media LLC
Date: 04-07-2022
DOI: 10.1038/S41586-022-04893-W
Abstract: The standard model of particle physics 1–4 describes the known fundamental particles and forces that make up our Universe, with the exception of gravity. One of the central features of the standard model is a field that permeates all of space and interacts with fundamental particles 5–9 . The quantum excitation of this field, known as the Higgs field, manifests itself as the Higgs boson, the only fundamental particle with no spin. In 2012, a particle with properties consistent with the Higgs boson of the standard model was observed by the ATLAS and CMS experiments at the Large Hadron Collider at CERN 10,11 . Since then, more than 30 times as many Higgs bosons have been recorded by the ATLAS experiment, enabling much more precise measurements and new tests of the theory. Here, on the basis of this larger dataset, we combine an unprecedented number of production and decay processes of the Higgs boson to scrutinize its interactions with elementary particles. Interactions with gluons, photons, and W and Z bosons—the carriers of the strong, electromagnetic and weak forces—are studied in detail. Interactions with three third-generation matter particles (bottom ( b ) and top ( t ) quarks, and tau leptons ( τ )) are well measured and indications of interactions with a second-generation particle (muons, μ ) are emerging. These tests reveal that the Higgs boson discovered ten years ago is remarkably consistent with the predictions of the theory and provide stringent constraints on many models of new phenomena beyond the standard model.
Emulating the impact of additional proton–proton interactions in the ATLAS simulation by presampling sets of inelastic Monte Carlo events
Publisher: Springer Science and Business Media LLC
Date: 27-01-2022
DOI: 10.1007/S41781-021-00062-2
Abstract: The accurate simulation of additional interactions at the ATLAS experiment for the analysis of proton–proton collisions delivered by the Large Hadron Collider presents a significant challenge to the computing resources. During the LHC Run 2 (2015–2018), there were up to 70 inelastic interactions per bunch crossing, which need to be accounted for in Monte Carlo (MC) production. In this document, a new method to account for these additional interactions in the simulation chain is described. Instead of s ling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the inelastic interactions are pres led, independent of the hard scatter, and stored as combined events. Consequently, for each hard-scatter interaction, only one such pres led event needs to be added as part of the simulation chain. For the Run 2 simulation chain, with an average of 35 interactions per bunch crossing, this new method provides a substantial reduction in MC production CPU needs of around 20%, while reproducing the properties of the reconstructed quantities relevant for physics analyses with good accuracy.
Measurement of the Sensitivity of Two-Particle Correlations in
p p
Publisher: American Physical Society (APS)
Date: 16-10-2023
Search for a light charged Higgs boson in t → H±b decays, with H± → cb, in the lepton+jets final state in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 09-2023
Measurement of $$Z\gamma \gamma $$ production in pp collisions at $$\sqrt{s}= 13$$ TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 27-06-2023
DOI: 10.1140/EPJC/S10052-023-11579-8
Abstract: Cross-sections for the production of a Z boson in association with two photons are measured in proton–proton collisions at a centre-of-mass energy of 13 TeV. The data used correspond to an integrated luminosity of 139 fb $$^{-1}$$ - 1 recorded by the ATLAS experiment during Run 2 of the LHC. The measurements use the electron and muon decay channels of the Z boson, and a fiducial phase-space region where the photons are not radiated from the leptons. The integrated $$Z(\\rightarrow \\ell \\ell )\\gamma \\gamma $$ Z ( → ℓ ℓ ) γ γ cross-section is measured with a precision of 12% and differential cross-sections are measured as a function of six kinematic variables of the $$Z\\gamma \\gamma $$ Z γ γ system. The data are compared with predictions from MC event generators which are accurate to up to next-to-leading order in QCD. The cross-section measurements are used to set limits on the coupling strengths of dimension-8 operators in the framework of an effective field theory.
Measurement of the CP properties of Higgs boson interactions with $$\tau $$-leptons with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 04-07-2023
DOI: 10.1140/EPJC/S10052-023-11583-Y
Abstract: A study of the charge conjugation and parity ( $$\\textit{CP}$$ CP ) properties of the interaction between the Higgs boson and $$\\tau $$ τ -leptons is presented. The study is based on a measurement of $$\\textit{CP}$$ CP -sensitive angular observables defined by the visible decay products of $$\\tau $$ τ -leptons produced in Higgs boson decays. The analysis uses 139 fb $$^{-1}$$ - 1 of proton–proton collision data recorded at a centre-of-mass energy of $$\\sqrt{s}= 13$$ s = 13 TeV with the ATLAS detector at the Large Hadron Collider. Contributions from $$\\textit{CP}$$ CP -violating interactions between the Higgs boson and $$\\tau $$ τ -leptons are described by a single mixing angle parameter $$\\phi _{\\tau }$$ ϕ τ in the generalised Yukawa interaction. Without constraining the $$H\\rightarrow \\tau \\tau $$ H → τ τ signal strength to its expected value under the Standard Model hypothesis, the mixing angle $$\\phi _{\\tau }$$ ϕ τ is measured to be $$9^{\\circ } \\pm 16^{\\circ }$$ 9 ∘ ± 16 ∘ , with an expected value of $$0^{\\circ } \\pm 28^{\\circ }$$ 0 ∘ ± 28 ∘ at the 68% confidence level. The pure $$\\textit{CP}$$ CP -odd hypothesis is disfavoured at a level of 3.4 standard deviations. The results are compatible with the predictions for the Higgs boson in the Standard Model.
Search for type-III seesaw heavy leptons in dilepton final states in pp collisions at $$ \sqrt{s} = 13\,{\text {TeV}} $$ with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 03-2021
DOI: 10.1140/EPJC/S10052-021-08929-9
Abstract: A search for the pair production of heavy leptons as predicted by the type-III seesaw mechanism is presented. The search uses proton–proton collision data at a centre-of-mass energy of 13 TeV, corresponding to $$ 139\\,{\\text {fb}}^{-1} $$ 139 fb - 1 of integrated luminosity recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis focuses on the final state with two light leptons (electrons or muons) of different flavour and charge combinations, with at least two jets and large missing transverse momentum. No significant excess over the Standard Model expectation is observed. The results are translated into exclusion limits on heavy-lepton masses, and the observed lower limit on the mass of the type-III seesaw heavy leptons is 790 GeV at 95% confidence level.
Search for type-III seesaw heavy leptons in leptonic final states in pp collisions at $$\sqrt{s} = 13~\text {TeV}$$ with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 03-11-2022
DOI: 10.1140/EPJC/S10052-022-10785-0
Abstract: A search for the pair production of heavy leptons as predicted by the type-III seesaw mechanism is presented. The search uses proton–proton collision data at a centre-of-mass energy of 13 TeV, corresponding to $$139\\,\\text {fb}^{-1}$$ 139 fb - 1 of integrated luminosity recorded by the ATLAS detector during Run 2 of the Large Hadron Collider. The analysis focuses on final states with three or four electrons or muons from the possible decays of new heavy leptons via intermediate electroweak bosons. No significant deviations above the Standard Model expectation are observed upper and lower limits on the heavy lepton production cross-section and masses are derived respectively. These results are then combined for the first time with the ones already published by ATLAS using the channel with two leptons in the final state. The observed lower limit on the mass of the type-III seesaw heavy leptons combining two, three and four lepton channels together is 910 GeV at the 95% confidence level.
Charged-hadron production in pp, p+Pb, Pb+Pb, and Xe+Xe collisions at $$ \sqrt{s_{\textrm{NN}}} $$ = 5 TeV with the ATLAS detector at the LHC
Publisher: Springer Science and Business Media LLC
Date: 10-07-2023
Abstract: This paper presents measurements of charged-hadron spectra obtained in pp , p +Pb, and Pb+Pb collisions at $$ \sqrt{s} $$ s or $$ \sqrt{s_{\textrm{NN}}} $$ s NN = 5 . 02 TeV, and in Xe+Xe collisions at $$ \sqrt{s_{\textrm{NN}}} $$ s NN = 5 . 44 TeV. The data recorded by the ATLAS detector at the LHC have total integrated luminosities of 25 pb − 1 , 28 nb − 1 , 0.50 nb − 1 , and 3 μ b − 1 , respectively. The nuclear modification factors R p Pb and R AA are obtained by comparing the spectra in heavy-ion and pp collisions in a wide range of charged-particle transverse momenta and pseudorapidity. The nuclear modification factor R p Pb shows a moderate enhancement above unity with a maximum at p T ≈ 3 GeV the enhancement is stronger in the Pb-going direction. The nuclear modification factors in both Pb+Pb and Xe+Xe collisions feature a significant, centrality-dependent suppression. They show a similar distinct p T -dependence with a local maximum at p T ≈ 2 GeV and a local minimum at p T ≈ 7 GeV. This dependence is more distinguishable in more central collisions. No significant | η |-dependence is found. A comprehensive comparison with several theoretical predictions is also provided. They typically describe R AA better in central collisions and in the p T range from about 10 to 100 GeV.
Measurements of top-quark pair spin correlations in the $$e\mu $$ channel at $$\sqrt{s} = 13$$ TeV using pp collisions in the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 08-2020
DOI: 10.1140/EPJC/S10052-020-8181-6
Abstract: A measurement of observables sensitive to spin correlations in $$t\\bar{t}$$ t t ¯ production is presented, using 36.1 $$\\hbox {fb}^{-1}$$ fb - 1 of pp collision data at $$\\sqrt{s} = 13$$ s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. Differential cross-sections are measured in events with exactly one electron and one muon with opposite-sign electric charge as a function of the azimuthal opening angle and the absolute difference in pseudorapidity between the electron and muon candidates in the laboratory frame. The azimuthal opening angle is also measured as a function of the invariant mass of the $$t\\bar{t}$$ t t ¯ system. The measured differential cross-sections are compared to predictions by several NLO Monte Carlo generators and fixed-order calculations. The observed degree of spin correlation is somewhat higher than predicted by the generators used. The data are consistent with the prediction of one of the fixed-order calculations at NLO, but agree less well with higher-order predictions. Using these leptonic observables, a search is performed for pair production of supersymmetric top squarks decaying into Standard Model top quarks and light neutralinos. Top squark masses between 170 and 230 GeV are largely excluded at the 95% confidence level for kinematically allowed values of the neutralino mass.
Search for exotic decays of the Higgs boson into long-lived particles in pp collisions at $$ \sqrt{s} $$ = 13 TeV using displaced vertices in the ATLAS inner detector
Publisher: Springer Science and Business Media LLC
Date: 11-2021
Abstract: A novel search for exotic decays of the Higgs boson into pairs of long-lived neutral particles, each decaying into a bottom quark pair, is performed using 139 fb − 1 of $$ \\sqrt{s} $$ s = 13 TeV proton-proton collision data collected with the ATLAS detector at the LHC. Events consistent with the production of a Higgs boson in association with a leptonically decaying Z boson are analysed. Long-lived particle (LLP) decays are reconstructed from inner-detector tracks as displaced vertices with high mass and track multiplicity relative to Standard Model processes. The analysis selection requires the presence of at least two displaced vertices, effectively suppressing Standard Model backgrounds. The residual background contribution is estimated using a data-driven technique. No excess over Standard Model predictions is observed, and upper limits are set on the branching ratio of the Higgs boson to LLPs. Branching ratios above 10% are excluded at 95% confidence level for LLP mean proper lifetimes cτ as small as 4 mm and as large as 100 mm. For LLP masses below 40 GeV, these results represent the most stringent constraint in this lifetime regime.
Measurements of differential cross-sections in four-lepton events in 13 TeV proton-proton collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Abstract: Measurements of four-lepton differential and integrated fiducial cross-sections in events with two same-flavour, opposite-charge electron or muon pairs are presented. The data correspond to 139 fb − 1 of $$ \\sqrt{s} $$ s = 13 TeV proton-proton collisions, collected by the ATLAS detector during Run 2 of the Large Hadron Collider (2015–2018). The final state has contributions from a number of interesting Standard Model processes that dominate in different four-lepton invariant mass regions, including single Z boson production, Higgs boson production and on-shell ZZ production, with a complex mix of interference terms, and possible contributions from physics beyond the Standard Model. The differential cross-sections include the four-lepton invariant mass inclusively, in slices of other kinematic variables, and in different lepton flavour categories. Also measured are dilepton invariant masses, transverse momenta, and angular correlation variables, in four regions of four-lepton invariant mass, each dominated by different processes. The measurements are corrected for detector effects and are compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. The Z → 4 ℓ branching fraction is extracted, giving a value of (4 . 41 ± 0 . 30) × 10 − 6 . Constraints on effective field theory parameters and a model based on a spontaneously broken B − L gauge symmetry are also evaluated. Further reinterpretations can be performed with the provided information.
Search for pair-production of vector-like quarks in pp collision events at s
Publisher: Elsevier BV
Date: 08-2023
Search for heavy diboson resonances in semileptonic final states in pp collisions at $$\sqrt{s}=13$$ TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 12-2020
DOI: 10.1140/EPJC/S10052-020-08554-Y
Abstract: This paper reports on a search for heavy resonances decaying into WW , ZZ or WZ using proton–proton collision data at a centre-of-mass energy of $$\\sqrt{s}=13$$ s = 13 TeV. The data, corresponding to an integrated luminosity of 139 $$\\mathrm{fb}^{1}$$ fb 1 , were recorded with the ATLAS detector from 2015 to 2018 at the Large Hadron Collider. The search is performed for final states in which one W or Z boson decays leptonically, and the other W boson or Z boson decays hadronically. The data are found to be described well by expected backgrounds. Upper bounds on the production cross sections of heavy scalar, vector or tensor resonances are derived in the mass range 300–5000 GeV within the context of Standard Model extensions with warped extra dimensions or including a heavy vector triplet. Production through gluon–gluon fusion, Drell–Yan or vector-boson fusion are considered, depending on the assumed model.
Search for a new scalar resonance in flavour-changing neutral-current top-quark decays t → qX (q = u, c), with X → $$ b\overline{b} $$, in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV with the
Publisher: Springer Science and Business Media LLC
Date: 26-07-2023
Abstract: A search for flavour-changing neutral-current decays of a top quark into an up-type quark (either up or charm) and a light scalar particle X decaying into a bottom anti-bottom quark pair is presented. The search focuses on top-quark pair production where one top quark decays to qX , with X → $$ b\\overline{b} $$ b b ¯ , and the other top quark decays according to the Standard Model, with the W boson decaying leptonically. The final state is thus characterised by an isolated electron or muon and at least four jets. Events are categorised according to the multiplicity of jets and jets tagged as originating from b -quarks, and a neural network is used to discriminate between signal and background processes. The data analysed correspond to 139 fb − 1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, recorded with the ATLAS detector at the LHC. The 95% confidence-level upper limits between 0.019% and 0.062% are derived for the branching fraction $$ \\mathcal{B} $$ B ( t → uX ) and between 0.018% and 0.078% for the branching fraction $$ \\mathcal{B} $$ B ( t → cX ), for masses of the scalar particle X between 20 and 160 GeV.
Search for pair-produced vector-like top and bottom partners in events with large missing transverse momentum in pp collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 10-08-2023
DOI: 10.1140/EPJC/S10052-023-11790-7
Abstract: A search for pair-produced vector-like quarks using events with exactly one lepton ( e or $$\\mu $$ μ ), at least four jets including at least one b -tagged jet, and large missing transverse momentum is presented. Data from proton–proton collisions at a centre-of-mass energy of $$\\sqrt{s}=$$ s = 13 $$\\text {TeV}$$ TeV , recorded by the ATLAS detector at the LHC from 2015 to 2018 and corresponding to an integrated luminosity of 139 fb $$^{-1}$$ - 1 , are analysed. Vector-like partners T and B of the top and bottom quarks are considered, as is a vector-like X with charge $$+5/3$$ + 5 / 3 , assuming their decay into a W , Z , or Higgs boson and a third-generation quark. No significant deviations from the Standard Model expectation are observed. Upper limits on the production cross-section of T and B quark pairs as a function of their mass are derived for various decay branching ratio scenarios. The strongest lower limits on the masses are 1.59 $$\\text {TeV}$$ TeV assuming mass-degenerate vector-like quarks and branching ratios corresponding to the weak-isospin doublet model, and 1.47 $$\\text {TeV}$$ TeV (1.46 $$\\text {TeV}$$ TeV ) for exclusive $$T \\rightarrow Zt$$ T → Z t ( $$B/X \\rightarrow Wt$$ B / X → W t ) decays. In addition, lower limits on the T and B quark masses are derived for all possible branching ratios.
Search for direct production of electroweakinos in final states with one lepton, missing transverse momentum and a Higgs boson decaying into two b-jets in $$pp$$ collisions at $$\sqrt{s}=13$$ TeV with
Publisher: Springer Science and Business Media LLC
Date: 08-2020
DOI: 10.1140/EPJC/S10052-020-8050-3
Abstract: The results of a search for electroweakino pair production $$pp \\rightarrow \\tilde{\\chi }^\\pm _1 \\tilde{\\chi }^0_2$$ p p → χ ~ 1 ± χ ~ 2 0 in which the chargino ( $$\\tilde{\\chi }^\\pm _1$$ χ ~ 1 ± ) decays into a W boson and the lightest neutralino ( $$\\tilde{\\chi }^0_1$$ χ ~ 1 0 ), while the heavier neutralino ( $$\\tilde{\\chi }^0_2$$ χ ~ 2 0 ) decays into the Standard Model 125 GeV Higgs boson and a second $$\\tilde{\\chi }^0_1$$ χ ~ 1 0 are presented. The signal selection requires a pair of b -tagged jets consistent with those from a Higgs boson decay, and either an electron or a muon from the W boson decay, together with missing transverse momentum from the corresponding neutrino and the stable neutralinos. The analysis is based on data corresponding to 139 $$\\mathrm {fb}^{-1}$$ fb - 1 of $$\\sqrt{s}=13$$ s = 13 TeV pp collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. No statistically significant evidence of an excess of events above the Standard Model expectation is found. Limits are set on the direct production of the electroweakinos in simplified models, assuming pure wino cross-sections. Masses of $$\\tilde{\\chi }^{\\pm }_{1}/\\tilde{\\chi }^{0}_{2}$$ χ ~ 1 ± / χ ~ 2 0 up to 740 GeV are excluded at 95% confidence level for a massless $$\\tilde{\\chi }^{0}_{1}$$ χ ~ 1 0 .
Measurements of sensor radiation damage in the ATLAS inner detector using leakage currents
Publisher: IOP Publishing
Date: 08-2021
DOI: 10.1088/1748-0221/16/08/P08025
Abstract: Non-ionizing energy loss causes bulk damage to the silicon sensors of the ATLAS pixel and strip detectors. This damage has important implications for data-taking operations, charged-particle track reconstruction, detector simulations, and physics analysis. This paper presents simulations and measurements of the leakage current in the ATLAS pixel detector and semiconductor tracker as a function of location in the detector and time, using data collected in Run 1 (2010–2012) and Run 2 (2015–2018) of the Large Hadron Collider. The extracted fluence shows a much stronger | z |-dependence in the innermost layers than is seen in simulation. Furthermore, the overall fluence on the second innermost layer is significantly higher than in simulation, with better agreement in layers at higher radii. These measurements are important for validating the simulation models and can be used in part to justify safety factors for future detector designs and interventions.
Measurements of Zγ+jets differential cross sections in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 10-07-2023
Abstract: Differential cross-section measurements of Zγ production in association with hadronic jets are presented, using the full 139 fb − 1 dataset of $$ \\sqrt{s} $$ s = 13 TeV proton–proton collisions collected by the ATLAS detector during Run 2 of the LHC. Distributions are measured using events in which the Z boson decays leptonically and the photon is usually radiated from an initial-state quark. Measurements are made in both one and two observables, including those sensitive to the hard scattering in the event and others which probe additional soft and collinear radiation. Different Standard Model predictions, from both parton-shower Monte Carlo simulation and fixed-order QCD calculations, are compared with the measurements. In general, good agreement is observed between data and predictions from MATRIX and MiNNLO PS , as well as next-to-leading-order predictions from M ad G raph 5_ a MC@NLO and S herpa .
Measurement of the t$$ \overline{t} $$t$$ \overline{t} $$ production cross section in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 11-2021
Abstract: A measurement of four-top-quark production using proton-proton collision data at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the Large Hadron Collider corresponding to an integrated luminosity of 139 fb − 1 is presented. Events are selected if they contain a single lepton (electron or muon) or an opposite-sign lepton pair, in association with multiple jets. The events are categorised according to the number of jets and how likely these are to contain b -hadrons. A multivariate technique is then used to discriminate between signal and background events. The measured four-top-quark production cross section is found to be $$ {26}_{-15}^{+17} $$ 26 − 15 + 17 fb, with a corresponding observed (expected) significance of 1.9 (1.0) standard deviations over the background-only hypothesis. The result is combined with the previous measurement performed by the ATLAS Collaboration in the multilepton final state. The combined four-top-quark production cross section is measured to be $$ {24}_{-6}^{+7} $$ 24 − 6 + 7 fb, with a corresponding observed (expected) signal significance of 4.7 (2.6) standard deviations over the background-only predictions. It is consistent within 2.0 standard deviations with the Standard Model expectation of 12 . 0 ± 2 . 4 fb.
Longitudinal Flow Decorrelations in
Xe + Xe Publisher:
American Physical Society (APS)
Date:
24-03-2021
Publisher: American Physical Society (APS)
Date: 24-03-2021
Measurements of multijet event isotropies using optimal transport with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 10-10-2023
Higgs boson production cross-section measurements and their EFT interpretation in the $$4\ell $$ decay channel at $$\sqrt{s}=$$13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 10-2020
DOI: 10.1140/EPJC/S10052-020-8227-9
Abstract: Higgs boson properties are studied in the four-lepton decay channel (where lepton = e , $$\\mu $$ μ ) using 139 $$\\hbox {fb}^{-1}$$ fb - 1 of proton–proton collision data recorded at $$\\sqrt{s}=$$ s = 13 TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive cross-section times branching ratio for $$H\\rightarrow ZZ^*$$ H → Z Z ∗ decay is measured to be $$1.34 \\pm 0.12$$ 1.34 ± 0.12 pb for a Higgs boson with absolute rapidity below 2.5, in good agreement with the Standard Model prediction of $$1.33 \\pm 0.08$$ 1.33 ± 0.08 pb. Cross-sections times branching ratio are measured for the main Higgs boson production modes in several exclusive phase-space regions. The measurements are interpreted in terms of coupling modifiers and of the tensor structure of Higgs boson interactions using an effective field theory approach. Exclusion limits are set on the CP-even and CP-odd ‘beyond the Standard Model’ couplings of the Higgs boson to vector bosons, gluons and top quarks.
Measurement of the transverse momentum distribution of Drell–Yan lepton pairs in proton–proton collisions at $$\sqrt{s}=13\,$$TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 07-2020
DOI: 10.1140/EPJC/S10052-020-8001-Z
Abstract: This paper describes precision measurements of the transverse momentum $$p_\\mathrm {T}^{\\ell \\ell }$$ p T ℓ ℓ ( $$\\ell =e,\\mu $$ ℓ = e , μ ) and of the angular variable $$\\phi ^{*}_{\\eta }$$ ϕ η ∗ distributions of Drell–Yan lepton pairs in a mass range of 66–116 GeV. The analysis uses data from 36.1 fb $$^{-1}$$ - 1 of proton–proton collisions at a centre-of-mass energy of $$\\sqrt{s}=13\\,$$ s = 13 TeV collected by the ATLAS experiment at the LHC in 2015 and 2016. Measurements in electron-pair and muon-pair final states are performed in the same fiducial volumes, corrected for detector effects, and combined. Compared to previous measurements in proton–proton collisions at $$\\sqrt{s}=7$$ s = 7 and $$8\\,$$ 8 TeV, these new measurements probe perturbative QCD at a higher centre-of-mass energy with a different composition of initial states. They reach a precision of 0.2 $$\\%$$ % for the normalized spectra at low values of $$p_\\mathrm {T}^{\\ell \\ell }$$ p T ℓ ℓ . The data are compared with different QCD predictions, where it is found that predictions based on resummation approaches can describe the full spectrum within uncertainties.
Searches for exclusive Higgs and Z boson decays into a vector quarkonium state and a photon using 139 fb$$^{-1}$$ of ATLAS $$\sqrt{s}=13$$ TeV proton–proton collision data
Publisher: Springer Science and Business Media LLC
Date: 05-09-2023
Search for long-lived, massive particles in events with displaced vertices and multiple jets in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 29-06-2023
Abstract: A search for long-lived particles decaying into hadrons is presented. The analysis uses 139 fb − 1 of pp collision data collected at $$ \\sqrt{s} $$ s = 13 TeV by the ATLAS detector at the LHC using events that contain multiple energetic jets and a displaced vertex. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particles decaying in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are used to set limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and on scenarios with pair-production of supersymmetric particles with long-lived electroweakinos that decay via a small R -parity-violating coupling. The pair-production of electroweakinos with masses below 1.5 TeV is excluded for mean proper lifetimes in the range from 0.03 ns to 1 ns. When produced in the decay of $$ m\\left(\\overset{\\sim }{g}\\right) $$ m g ~ = 2 . 4 TeV gluinos, electroweakinos with $$ m\\left({\\overset{\\sim }{\\chi}}_1^0\\right) $$ m χ ~ 1 0 = 1 . 5 TeV are excluded with lifetimes in the range of 0.02 ns to 4 ns.
Measurement of the polarisation of single top quarks and antiquarks produced in the t-channel at $$ \sqrt{s} $$ = 13 TeV and bounds on the tWb dipole operator from the ATLAS experiment
Publisher: Springer Science and Business Media LLC
Date: 09-11-2022
Abstract: A simultaneous measurement of the three components of the top-quark and top-antiquark polarisation vectors in t -channel single-top-quark production is presented. This analysis is based on data from proton–proton collisions at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 139 fb − 1 , collected with the ATLAS detector at the LHC. Selected events contain exactly one isolated electron or muon, large missing transverse momentum and exactly two jets, one being b -tagged. Stringent selection requirements are applied to discriminate t -channel single-top-quark events from the background contributions. The top-quark and top-antiquark polarisation vectors are measured from the distributions of the direction cosines of the charged-lepton momentum in the top-quark rest frame. The three components of the polarisation vector for the selected top-quark event s le are $$ {P}_{x^{\\prime }} $$ P x ′ = 0 . 01 ± 0 . 18, $$ {P}_{y^{\\prime }} $$ P y ′ = − 0 . 029 ± 0 . 027, $$ {P}_{z^{\\prime }} $$ P z ′ = 0 . 91 ± 0 . 10 and for the top-antiquark event s le they are $$ {P}_{x^{\\prime }} $$ P x ′ = − 0 . 02 ± 0 . 20, $$ {P}_{y^{\\prime }} $$ P y ′ = − 0 . 007 ± 0 . 051, $$ {P}_{z^{\\prime }} $$ P z ′ = 0 . 79 ± 0 . 16. Normalised differential cross-sections corrected to a fiducial region at the stable-particle level are presented as a function of the charged-lepton angles for top-quark and top-antiquark events inclusively and separately. These measurements are in agreement with Standard Model predictions. The angular differential cross-sections are used to derive bounds on the complex Wilson coefficient of the dimension-six $$ \\mathcal{O} $$ O tW operator in the framework of an effective field theory. The obtained bounds are C tW ∈ [ − 0 . 9 , 1 . 4] and C itW ∈ [ − 0 . 8 , 0 . 2], both at 95% confidence level.
Search for Heavy Higgs Bosons Decaying into Two Tau Leptons with the ATLAS Detector Using
p p
Publisher:
American Physical Society (APS)
Date:
27-07-2020
Publisher: American Physical Society (APS)
Date: 27-07-2020
Measurements of the Higgs boson inclusive and differential fiducial cross-sections in the diphoton decay channel with pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 02-08-2022
Abstract: A measurement of inclusive and differential fiducial cross-sections for the production of the Higgs boson decaying into two photons is performed using 139 fb − 1 of proton-proton collision data recorded at $$ \\sqrt{s} $$ s = 13 TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive cross-section times branching ratio, in a fiducial region closely matching the experimental selection, is measured to be 67 ± 6 fb, which is in agreement with the state-of-the-art Standard Model prediction of 64 ± 4 fb. Extrapolating this result to the full phase space and correcting for the branching ratio, the total cross-section for Higgs boson production is estimated to be 58 ± 6 pb. In addition, the cross-sections in four fiducial regions sensitive to various Higgs boson production modes and differential cross-sections as a function of either one or two of several observables are measured. All the measurements are found to be in agreement with the Standard Model predictions. The measured transverse momentum distribution of the Higgs boson is used as an indirect probe of the Yukawa coupling of the Higgs boson to the bottom and charm quarks. In addition, five differential cross-section measurements are used to constrain anomalous Higgs boson couplings to vector bosons in the Standard Model effective field theory framework.
Search for pair production of third-generation scalar leptoquarks decaying into a top quark and a τ-lepton in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 30-10-2021
Abstract: A search for pair production of third-generation scalar leptoquarks decaying into a top quark and a τ -lepton is presented. The search is based on a dataset of pp collisions at $$ \\sqrt{s} $$ s = 13 TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb − 1 . Events are selected if they have one light lepton (electron or muon) and at least one hadronically decaying τ -lepton, or at least two light leptons. In addition, two or more jets, at least one of which must be identified as containing b -hadrons, are required. Six final states, defined by the multiplicity and flavour of lepton candidates, are considered in the analysis. Each of them is split into multiple event categories to simultaneously search for the signal and constrain several leading backgrounds. The signal-rich event categories require at least one hadronically decaying τ -lepton candidate and exploit the presence of energetic final-state objects, which is characteristic of signal events. No significant excess above the Standard Model expectation is observed in any of the considered event categories, and 95% CL upper limits are set on the production cross section as a function of the leptoquark mass, for different assumptions about the branching fractions into tτ and bν . Scalar leptoquarks decaying exclusively into tτ are excluded up to masses of 1 . 43 TeV while, for a branching fraction of 50% into tτ , the lower mass limit is 1 . 22 TeV.
Exclusive dimuon production in ultraperipheral
Pb + Pb
Publisher: American Physical Society (APS)
Date: 19-08-2021
Determination of the parton distribution functions of the proton from ATLAS measurements of differential W± and Z boson production in association with jets
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Abstract: This article presents a new set of proton parton distribution functions, ATLASepWZVjet20, produced in an analysis at next-to-next-to-leading order in QCD. The new data sets considered are the measurements of W + and W − boson and Z boson production in association with jets in pp collisions at $$ \\sqrt{s} $$ s = 8 TeV performed by the ATLAS experiment at the LHC with integrated luminosities of 20 . 2 fb − 1 and 19 . 9 fb − 1 , respectively. The analysis also considers the ATLAS measurements of differential W ± and Z boson production at $$ \\sqrt{s} $$ s = 7 TeV with an integrated luminosity of 4 . 6 fb − 1 and deep-inelastic-scattering data from e ± p collisions at the HERA accelerator. An improved determination of the sea-quark densities at high Bjorken x is shown, while confirming a strange-quark density similar in size to the up- and down-sea-quark densities in the range x ≲ 0 . 02 found by previous ATLAS analyses.
Measurements of differential cross sections of Higgs boson production through gluon fusion in the $$H\rightarrow WW^{*}\rightarrow e\nu \mu \nu $$ final state at $$\sqrt{s} = 13$$ TeV with the ATLAS d
Publisher: Springer Science and Business Media LLC
Date: 09-2023
Model-independent search for the presence of new physics in events including H → γγ with $$ \sqrt{s} $$ = 13 TeV pp data recorded by the ATLAS detector at the LHC
Publisher: Springer Science and Business Media LLC
Date: 24-07-2023
Abstract: A model-independent search for new physics leading to final states containing a Higgs boson, with a mass of 125.09 GeV, decaying to a pair of photons is performed with 139 fb − 1 of $$ \\sqrt{s} $$ s = 13 TeV pp collision data recorded by the ATLAS detector at the Large Hadron Collider at CERN. This search examines 22 final states categorized by the objects that are produced in association with the Higgs boson. These objects include isolated electrons or muons, hadronically decaying τ -leptons, additional photons, missing transverse momentum, and hadronic jets, as well as jets that are tagged as containing a b -hadron. No significant excesses above Standard Model expectations are observed and limits on the production cross section at 95% confidence level are set. Detector efficiencies are reported for all 22 signal regions, which can be used to convert detector-level cross-section limits reported in this paper to particle-level cross-section constraints.
Measurement of Higgs boson decay into b-quarks in associated production with a top-quark pair in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 17-06-2022
Abstract: The associated production of a Higgs boson and a top-quark pair is measured in events characterised by the presence of one or two electrons or muons. The Higgs boson decay into a b -quark pair is used. The analysed data, corresponding to an integrated luminosity of 139 fb − 1 , were collected in proton-proton collisions at the Large Hadron Collider between 2015 and 2018 at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV. The measured signal strength, defined as the ratio of the measured signal yield to that predicted by the Standard Model, is $$ {0.35}_{-0.34}^{+0.36} $$ 0.35 − 0.34 + 0.36 . This result is compatible with the Standard Model prediction and corresponds to an observed (expected) significance of 1.0 (2.7) standard deviations. The signal strength is also measured differentially in bins of the Higgs boson transverse momentum in the simplified template cross-section framework, including a bin for specially selected boosted Higgs bosons with transverse momentum above 300 GeV.
Search in diphoton and dielectron final states for displaced production of Higgs or
Z
Publisher: American Physical Society (APS)
Date: 19-07-2023
Measurements of inclusive and differential cross-sections of combined $$ t\overline{t}\gamma $$ and tWγ production in the eμ channel at 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 09-2020
Abstract: Inclusive and differential cross-sections for the production of top quarks in association with a photon are measured with proton-proton collision data corresponding to an integrated luminosity of 139 fb − 1 . The data were collected by the ATLAS detector at the LHC during Run 2 between 2015 and 2018 at a centre-of-mass energy of 13 TeV. The measurements are performed in a fiducial volume defined at parton level. Events with exactly one photon, one electron and one muon of opposite sign, and at least two jets, of which at least one is b -tagged, are selected. The fiducial cross-section is measured to be $$ {39.6}_{-2.3}^{+2.7} $$ 39.6 − 2.3 + 2.7 fb. Differential cross-sections as functions of several observables are compared with state-of-the-art Monte Carlo simulations and next-to-leading-order theoretical calculations. These include cross-sections as functions of photon kinematic variables, angular variables related to the photon and the leptons, and angular separations between the two leptons in the event. All measurements are in agreement with the predictions from the Standard Model.
Search for periodic signals in the dielectron and diphoton invariant mass spectra using 139 fb−1 of pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 13-10-2023
Operation of the ATLAS trigger system in Run 2
Publisher: IOP Publishing
Date: 02-10-2020
Search for new phenomena in events with an energetic jet and missing transverse momentum in
p p
Publisher:
American Physical Society (APS)
Date:
10-06-2021
Publisher: American Physical Society (APS)
Date: 10-06-2021
Search for flavour-changing neutral-current interactions of a top quark and a gluon in pp collisions at $$\sqrt{s}=13$$ TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 04-2022
DOI: 10.1140/EPJC/S10052-022-10182-7
Abstract: A search is presented for the production of a single top quark via left-handed flavour-changing neutral-current (FCNC) interactions of a top quark, a gluon and an up or charm quark. Two production processes are considered: $$u+g\rightarrow t$$ u + g → t and $$c+g\rightarrow t$$ c + g → t . The analysis is based on proton–proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. The data set corresponds to an integrated luminosity of 139 fb $$^{-1}$$ - 1 . Events with exactly one electron or muon, exactly one b -tagged jet and missing transverse momentum are selected, resembling the decay products of a singly produced top quark. Neural networks based on kinematic variables differentiate between events from the two signal processes and events from background processes. The measured data are consistent with the background-only hypothesis, and limits are set on the production cross-sections of the signal processes: $$\sigma (u+g\rightarrow t)\times \mathcal {B}(t\rightarrow Wb)\times \mathcal {B}(W\rightarrow \ell \nu ) .0\,$$ σ ( u + g → t ) × B ( t → W b ) × B ( W → ℓ ν ) 3.0 pb and $$\sigma (c+g\rightarrow t)\times \mathcal {B}(t\rightarrow Wb)\times \mathcal {B}(W\rightarrow \ell \nu ) .7\,$$ σ ( c + g → t ) × B ( t → W b ) × B ( W → ℓ ν ) 4.7 pb at the 95% confidence level, with $$\mathcal {B}(W\rightarrow \ell \nu )=0.325$$ B ( W → ℓ ν ) = 0.325 being the sum of branching ratios of all three leptonic decay modes of the W boson. Based on the framework of an effective field theory, the cross-section limits are translated into limits on the strengths of the tug and tcg couplings occurring in the theory: $$|C^{\,ut}_{uG}|/\Lambda ^2 0.057\,$$ | C uG u t | / Λ 2 0.057 TeV $$^{-2}$$ - 2 and $$|C^{\,ct}_{uG}|/\Lambda ^2 0.14\,$$ | C uG c t | / Λ 2 0.14 TeV $$^{-2}$$ - 2 . These bounds correspond to limits on the branching ratios of FCNC-induced top-quark decays: $$\mathcal {B}(t\rightarrow u+g) 0.61\times 10^{-4}$$ B ( t → u + g ) 0.61 × 10 - 4 and $$\mathcal {B}(t\rightarrow c+g) 3.7\times 10^{-4}$$ B ( t → c + g ) 3.7 × 10 - 4 .
Search for trilepton resonances from chargino and neutralino pair production in
s
Publisher:
American Physical Society (APS)
Date:
07-06-2021
Publisher: American Physical Society (APS)
Date: 07-06-2021
Measurements of Higgs boson production cross-sections in the H → τ+τ− decay channel in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 18-08-2022
Abstract: Measurements of the production cross-sections of the Standard Model (SM) Higgs boson ( H ) decaying into a pair of τ -leptons are presented. The measurements use data collected with the ATLAS detector from pp collisions produced at the Large Hadron Collider at a centre-of-mass energy of $$ \sqrt{s} $$ s = 13 TeV, corresponding to an integrated luminosity of 139 fb − 1 . Leptonic ( τ → ℓν ℓ ν τ ) and hadronic ( τ → hadrons ν τ ) decays of the τ -lepton are considered. All measurements account for the branching ratio of H → ττ and are performed with a requirement |y H | 2 . 5, where y H is the true Higgs boson rapidity. The cross-section of the pp → H → ττ process is measured to be 2 . 94 ± $$ 0.21{\left(\mathrm{stat}\right)}_{-0.32}^{+0.37} $$ 0.21 stat − 0.32 + 0.37 (syst) pb, in agreement with the SM prediction of 3 . 17 ± 0 . 09 pb. Inclusive cross-sections are determined separately for the four dominant production modes: 2 . 65 ± $$ 0.41{\left(\mathrm{stat}\right)}_{-0.67}^{+0.91} $$ 0.41 stat − 0.67 + 0.91 (syst) pb for gluon-gluon fusion, 0 . 197 ± $$ 0.028{\left(\mathrm{stat}\right)}_{-0.026}^{+0.032} $$ 0.028 stat − 0.026 + 0.032 (syst) pb for vector-boson fusion, 0 . 115 ± $$ 0.058{\left(\mathrm{stat}\right)}_{-0.040}^{+0.042} $$ 0.058 stat − 0.040 + 0.042 (syst) pb for vector-boson associated production, and 0 . 033 ± $$ 0.031{\left(\mathrm{stat}\right)}_{-0.017}^{+0.022} $$ 0.031 stat − 0.017 + 0.022 (syst) pb for top-quark pair associated production. Measurements in exclusive regions of the phase space, using the simplified template cross-section framework, are also performed. All results are in agreement with the SM predictions.
Search for resonant and non-resonant Higgs boson pair production in the $$ b\overline{b}{\tau}^{+}{\tau}^{-} $$ decay channel using 13 TeV pp collision data from the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 05-07-2023
Abstract: A search for Higgs boson pair production in events with two b -jets and two τ -leptons is presented, using a proton–proton collision dataset with an integrated luminosity of 139 fb − 1 collected at $$ \\sqrt{s} $$ s = 13 TeV by the ATLAS experiment at the LHC. Higgs boson pairs produced non-resonantly or in the decay of a narrow scalar resonance in the mass range from 251 to 1600 GeV are targeted. Events in which at least one τ -lepton decays hadronically are considered, and multivariate discriminants are used to reject the backgrounds. No significant excess of events above the expected background is observed in the non-resonant search. The largest excess in the resonant search is observed at a resonance mass of 1 TeV, with a local (global) significance of 3 . 1 σ (2 . 0 σ ). Observed (expected) 95% confidence-level upper limits are set on the non-resonant Higgs boson pair-production cross-section at 4.7 (3.9) times the Standard Model prediction, assuming Standard Model kinematics, and on the resonant Higgs boson pair-production cross-section at between 21 and 900 fb (12 and 840 fb), depending on the mass of the narrow scalar resonance.
Measurement of azimuthal anisotropy of muons from charm and bottom hadrons in Pb+Pb collisions at
Publisher:
Elsevier BV
Date:
08-2020
Publisher: Elsevier BV
Date: 08-2020
Measurements of observables sensitive to colour reconnection in $$t{\bar{t}}$$ events with the ATLAS detector at $$\sqrt{s} =$$ 13 TeV
Publisher: Springer Science and Business Media LLC
Date: 20-06-2023
DOI: 10.1140/EPJC/S10052-023-11479-X
Abstract: A measurement of observables sensitive to effects of colour reconnection in top-quark pair-production events is presented using 139 $$\\hbox {fb}^{-1}$$ fb - 1 of 13 TeV proton–proton collision data collected by the ATLAS detector at the LHC. Events are selected by requiring exactly one isolated electron and one isolated muon with opposite charge and two or three jets, where exactly two jets are required to be b -tagged. For the selected events, measurements are presented for the charged-particle multiplicity, the scalar sum of the transverse momenta of the charged particles, and the same scalar sum in bins of charged-particle multiplicity. These observables are unfolded to the stable-particle level, thereby correcting for migration effects due to finite detector resolution, acceptance and efficiency effects. The particle-level measurements are compared with different colour reconnection models in Monte Carlo generators. These measurements disfavour some of the colour reconnection models and provide inputs to future optimisation of the parameters in Monte Carlo generators.
Searches for lepton-flavour-violating decays of the Higgs boson into eτ and μτ in $$ \sqrt{s} $$ = 13 TeV pp collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 21-07-2023
Abstract: This paper presents direct searches for lepton flavour violation in Higgs boson decays, H → eτ and H → μτ , performed using data collected with the ATLAS detector at the LHC. The searches are based on a data s le of proton-proton collisions at a centre-of-mass energy $$ \\sqrt{s} $$ s = 13 TeV, corresponding to an integrated luminosity of 138 fb − 1 . Leptonic ( τ → ℓν ℓ ν τ ) and hadronic ( τ → hadrons ν τ ) decays of the τ -lepton are considered. Two background estimation techniques are employed: the MC-template method, based on data-corrected simulation s les, and the Symmetry method, based on exploiting the symmetry between electrons and muons in the Standard Model backgrounds. No significant excess of events is observed and the results are interpreted as upper limits on lepton-flavour-violating branching ratios of the Higgs boson. The observed (expected) upper limits set on the branching ratios at 95% confidence level, $$ \\mathcal{B} $$ B ( H → eτ ) 0 . 20% (0 . 12%) and $$ \\mathcal{B} $$ B ( H → μτ ) 0 . 18% (0 . 09%), are obtained with the MC-template method from a simultaneous measurement of potential H → eτ and H → μτ signals. The best-fit branching ratio difference, $$ \\mathcal{B} $$ B ( H → μτ ) → $$ \\mathcal{B} $$ B ( H → eτ ), measured with the Symmetry method in the channel where the τ -lepton decays to leptons, is (0 . 25 ± 0 . 10)%, compatible with a value of zero within 2 . 5 σ .
Observation of gauge boson joint-polarisation states in W±Z production from pp collisions at s
Publisher:
Elsevier BV
Date:
08-2023
Publisher: Elsevier BV
Date: 08-2023
ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset
Publisher: Springer Science and Business Media LLC
Date: 31-07-2023
DOI: 10.1140/EPJC/S10052-023-11699-1
Abstract: The flavour-tagging algorithms developed by the ATLAS Collaboration and used to analyse its dataset of $$\\sqrt{s} = 13$$ s = 13 TeV pp collisions from Run 2 of the Large Hadron Collider are presented. These new tagging algorithms are based on recurrent and deep neural networks, and their performance is evaluated in simulated collision events. These developments yield considerable improvements over previous jet-flavour identification strategies. At the 77% b -jet identification efficiency operating point, light-jet (charm-jet) rejection factors of 170 (5) are achieved in a s le of simulated Standard Model $$t\\bar{t}$$ t t ¯ events similarly, at a c -jet identification efficiency of 30%, a light-jet ( b -jet) rejection factor of 70 (9) is obtained.
Two-particle azimuthal correlations in photonuclear ultraperipheral
Pb + Pb
Publisher:
American Physical Society (APS)
Date:
12-07-2021
Publisher: American Physical Society (APS)
Date: 12-07-2021
Search for bottom-squark pair production in
p p
Publisher:
American Physical Society (APS)
Date:
31-08-2021
Publisher: American Physical Society (APS)
Date: 31-08-2021
Two-particle Bose–Einstein correlations in $${ pp }$$ collisions at $$\mathbf {\sqrt{s} = 13}$$ TeV measured with the ATLAS detector at the LHC
Publisher: Springer Science and Business Media LLC
Date: 11-07-2022
DOI: 10.1140/EPJC/S10052-022-10472-0
Abstract: This paper presents studies of Bose–Einstein correlations (BEC) in proton–proton collisions at a centre-of-mass energy of 13 TeV, using data from the ATLAS detector at the CERN Large Hadron Collider. Data were collected in a special low-luminosity configuration with a minimum-bias trigger and a high-multiplicity track trigger, accumulating integrated luminosities of 151 $$\upmu $$ μ b $$^{-1}$$ - 1 and 8.4 nb $$^{-1}$$ - 1 , respectively. The BEC are measured for pairs of like-sign charged particles, each with $$|\eta | 2.5$$ | η | 2.5 , for two kinematic ranges: the first with particle $$p_{\mathrm {T}} 100$$ p T 100 MeV and the second with particle $$p_{\mathrm {T}} 500$$ p T 500 MeV. The BEC parameters, characterizing the source radius and particle correlation strength, are investigated as functions of charged-particle multiplicity (up to 300) and average transverse momentum of the pair (up to 1.5 GeV). The double-differential dependence on charged-particle multiplicity and average transverse momentum of the pair is also studied. The BEC radius is found to be independent of the charged-particle multiplicity for high charged-particle multiplicity (above 100), confirming a previous observation at lower energy. This saturation occurs independent of the transverse momentum of the pair.
Search for new non-resonant phenomena in high-mass dilepton final states with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 11-2020
Abstract: A search for new physics with non-resonant signals in dielectron and dimuon final states in the mass range above 2 TeV is presented. This is the first search for non-resonant signals in dilepton final states at the LHC to use a background estimate from the data. The data, corresponding to an integrated luminosity of 139 fb − 1 , were recorded by the ATLAS experiment in proton-proton collisions at a center-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV during Run 2 of the Large Hadron Collider. The benchmark signal signature is a two-quark and two-lepton contact interaction, which would enhance the dilepton event rate at the TeV mass scale. To model the contribution from background processes a functional form is fit to the dilepton invariant-mass spectra in data in a mass region below the region of interest. It is then extrapolated to a high-mass signal region to obtain the expected background there. No significant deviation from the expected background is observed in the data. Upper limits at 95% CL on the number of events and the visible cross-section times branching fraction for processes involving new physics are provided. Observed (expected) 95% CL lower limits on the contact interaction energy scale reach 35.8 (37.6) TeV.
Observation and Measurement of Forward Proton Scattering in Association with Lepton Pairs Produced via the Photon Fusion Mechanism at ATLAS
Publisher: American Physical Society (APS)
Date: 23-12-2020
Measurements of WH and ZH production in the $$H \rightarrow b\bar{b}$$ decay channel in pp collisions at $$13\,\text {Te}\text {V}$$ with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 02-2021
DOI: 10.1140/EPJC/S10052-020-08677-2
Abstract: Measurements of the Standard Model Higgs boson decaying into a $$b\\bar{b}$$ b b ¯ pair and produced in association with a W or Z boson decaying into leptons, using proton–proton collision data collected between 2015 and 2018 by the ATLAS detector, are presented. The measurements use collisions produced by the Large Hadron Collider at a centre-of-mass energy of $$\\sqrt{s} = 13\\,\\text {Te}\\text {V}$$ s = 13 Te , corresponding to an integrated luminosity of $$139\\,\\mathrm {fb}^{-1}$$ 139 fb - 1 . The production of a Higgs boson in association with a W or Z boson is established with observed (expected) significances of 4.0 (4.1) and 5.3 (5.1) standard deviations, respectively. Cross-sections of associated production of a Higgs boson decaying into bottom quark pairs with an electroweak gauge boson, W or Z , decaying into leptons are measured as a function of the gauge boson transverse momentum in kinematic fiducial volumes. The cross-section measurements are all consistent with the Standard Model expectations, and the total uncertainties vary from 30% in the high gauge boson transverse momentum regions to 85% in the low regions. Limits are subsequently set on the parameters of an effective Lagrangian sensitive to modifications of the WH and ZH processes as well as the Higgs boson decay into $$b\\bar{b}$$ b b ¯ .
Search for exclusive Higgs and Z boson decays to ωγ and Higgs boson decays to K⁎γ with the ATLAS detector
Publisher: Elsevier BV
Date: 10-2023
Search for New Phenomena in Final States with Two Leptons and One or No
b
Publisher:
American Physical Society (APS)
Date:
10-2021
Publisher: American Physical Society (APS)
Date: 10-2021
A search for an unexpected asymmetry in the production of e+μ− and e−μ+ pairs in proton–proton collisions recorded by the ATLAS detector at
Publisher:
Elsevier BV
Date:
07-2022
Publisher: Elsevier BV
Date: 07-2022
Search for leptonic charge asymmetry in $$ t\overline{t}W $$ production in final states with three leptons at $$ \sqrt{s} $$ = 13 TeV
Publisher: Springer Science and Business Media LLC
Date: 05-07-2023
Abstract: A search for the leptonic charge asymmetry ( $$ {A}_{\\textrm{c}}^{\\ell } $$ A c ℓ ) of top-quark-antiquark pair production in association with a W boson ( $$ t\\overline{t}W $$ t t ¯ W ) is presented. The search is performed using final states with exactly three charged light leptons (electrons or muons) and is based on $$ \\sqrt{s} $$ s = 13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider at CERN during the years 2015–2018, corresponding to an integrated luminosity of 139 fb − 1 . A profile-likelihood fit to the event yields in multiple regions corresponding to positive and negative differences between the pseudorapidities of the charged leptons from top-quark and top-antiquark decays is used to extract the charge asymmetry. At reconstruction level, the asymmetry is found to be −0 . 12 ± 0 . 14 (stat.) ± 0 . 05 (syst.). An unfolding procedure is applied to convert the result at reconstruction level into a charge-asymmetry value in a fiducial volume at particle level with the result of −0 . 11 ± 0 . 17 (stat.) ± 0 . 05 (syst.). The Standard Model expectations for these two observables are calculated using Monte Carlo simulations with next-to-leading-order plus parton shower precision in quantum chromodynamics and including next-to-leading-order electroweak corrections. They are $$ -{0.084}_{-0.003}^{+0.005} $$ − 0.084 − 0.003 + 0.005 (scale) ± 0 . 006 (MC stat.) and $$ -{0.063}_{-0.004}^{+0.007} $$ − 0.063 − 0.004 + 0.007 (scale) ± 0 . 004 (MC stat.) respectively, and in agreement with the measurements.
Search for boosted diphoton resonances in the 10 to 70 GeV mass range using 138 fb−1 of 13 TeV pp collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 20-07-2023
Abstract: A search for diphoton resonances in the mass range between 10 and 70 GeV with the ATLAS experiment at the Large Hadron Collider (LHC) is presented. The analysis is based on pp collision data corresponding to an integrated luminosity of 138 fb − 1 at a centre-of-mass energy of 13 TeV recorded from 2015 to 2018. Previous searches for diphoton resonances at the LHC have explored masses down to 65 GeV, finding no evidence of new particles. This search exploits the particular kinematics of events with pairs of closely spaced photons reconstructed in the detector, allowing examination of invariant masses down to 10 GeV. The presented strategy covers a region previously unexplored at hadron colliders because of the experimental challenges of recording low-energy photons and estimating the backgrounds. No significant excess is observed and the reported limits provide the strongest bound on promptly decaying axion-like particles coupling to gluons and photons for masses between 10 and 70 GeV.
Measurement of the Higgs boson mass in the H → ZZ⁎ → 4ℓ decay channel using 139 fb−1 of s
Publisher:
Elsevier BV
Date:
08-2023
Publisher: Elsevier BV
Date: 08-2023
Observation of an Excess of Dicharmonium Events in the Four-Muon Final State with the ATLAS Detector
Publisher: American Physical Society (APS)
Date: 13-10-2023
Search for top squarks in events with a Higgs or Z boson using 139 fb$$^{-1}$$ of pp collision data at $$\sqrt{s}=13$$ TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 11-2020
DOI: 10.1140/EPJC/S10052-020-08469-8
Abstract: This paper presents a search for direct top squark pair production in events with missing transverse momentum plus either a pair of jets consistent with Standard Model Higgs boson decay into b -quarks or a same-flavour opposite-sign dilepton pair with an invariant mass consistent with a Z boson. The analysis is performed using the proton–proton collision data at $$\\sqrt{s}=13$$ s = 13 TeV collected with the ATLAS detector during the LHC Run-2, corresponding to an integrated luminosity of 139 fb $$^{-1}$$ - 1 . No excess is observed in the data above the Standard Model predictions. The results are interpreted in simplified models featuring direct production of pairs of either the lighter top squark ( $$\\tilde{t}_1$$ t ~ 1 ) or the heavier top squark ( $$\\tilde{t}_2$$ t ~ 2 ), excluding at 95% confidence level $$\\tilde{t}_1$$ t ~ 1 and $$\\tilde{t}_2$$ t ~ 2 masses up to about 1220 and 875 GeV, respectively.
Observation of photon-induced W+W− production in pp collisions at s Publisher:
Elsevier BV
Date:
05-2021
Publisher: Elsevier BV
Date: 05-2021
Search for pairs of muons with small displacements in pp collisions at s Publisher:
Elsevier BV
Date:
11-2023
Publisher: Elsevier BV
Date: 11-2023
Search for Higgs boson pair production in association with a vector boson in pp collisions at $$\sqrt{s}=13\,\text {TeV}$$ with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 20-06-2023
DOI: 10.1140/EPJC/S10052-023-11559-Y
Abstract: This paper reports a search for Higgs boson pair ( hh ) production in association with a vector boson ( $$W\\ {\\text {o}r}\\ Z$$ W o r Z ) using 139 fb $$^{-1}$$ - 1 of proton–proton collision data at $$\\sqrt{s}=13\\,\\text {TeV}$$ s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. The search is performed in final states in which the vector boson decays leptonically ( $$W\\rightarrow \\ell \\nu ,\\, Z\\rightarrow \\ell \\ell ,\\nu \\nu $$ W → ℓ ν , Z → ℓ ℓ , ν ν with $$\\ell =e, \\mu $$ ℓ = e , μ ) and the Higgs bosons each decay into a pair of b -quarks. It targets Vhh signals from both non-resonant hh production, present in the Standard Model (SM), and resonant hh production, as predicted in some SM extensions. A 95% confidence-level upper limit of 183 (87) times the SM cross-section is observed (expected) for non-resonant Vhh production when assuming the kinematics are as expected in the SM. Constraints are also placed on Higgs boson coupling modifiers. For the resonant search, upper limits on the production cross-sections are derived for two specific models: one is the production of a vector boson along with a neutral heavy scalar resonance H , in the mass range 260–1000 GeV, that decays into hh , and the other is the production of a heavier neutral pseudoscalar resonance A that decays into a Z boson and H boson, where the A boson mass is 360–800 GeV and the H boson mass is 260–400 GeV. Constraints are also derived in the parameter space of two-Higgs-doublet models.
Search for single production of a vectorlike
T
Publisher: American Physical Society (APS)
Date: 25-05-2022
New techniques for jet calibration with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 28-07-2021
DOI: 10.1140/EPJC/S10052-023-11837-9
Abstract: A determination of the jet energy scale is presented using proton–proton collision data with a centre-of-mass energy of $$\\sqrt{s}=13$$ s = 13 TeV, corresponding to an integrated luminosity of 140 fb $$^{-1}$$ - 1 collected using the ATLAS detector at the LHC. Jets are reconstructed using the ATLAS particle-flow method that combines charged-particle tracks and topo-clusters formed from energy deposits in the calorimeter cells. The anti- $$k_\\textrm{t}$$ k t jet algorithm with radius parameter $$R=0.4$$ R = 0.4 is used to define the jet. Novel jet energy scale calibration strategies developed for the LHC Run 2 are reported that lay the foundation for the jet calibration in Run 3. Jets are calibrated with a series of simulation-based corrections, including state-of-the-art techniques in jet calibration such as machine learning methods and novel in situ calibrations to achieve better performance than the baseline calibration derived using up to 81 fb $$^{-1}$$ - 1 of Run 2 data. The performance of these new techniques is then examined in the in situ measurements by exploiting the transverse momentum balance between a jet and a reference object. The b -quark jet energy scale using particle flow jets is measured for the first time with around 1% precision using $$\\gamma $$ γ +jet events.
Search for charged-lepton-flavour violation in Z-boson decays with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 07-2021
DOI: 10.1038/S41567-021-01225-Z
Abstract: Leptons with essentially the same properties apart from their mass are grouped into three families (or flavours). The number of leptons of each flavour is conserved in interactions, but this is not imposed by fundamental principles. Since the formulation of the standard model of particle physics, the observation of flavour oscillations among neutrinos has shown that lepton flavour is not conserved in neutrino weak interactions. So far, there has been no experimental evidence that this also occurs in interactions between charged leptons. Such an observation would be a sign of undiscovered particles or a yet unknown type of interaction. Here the ATLAS experiment at the Large Hadron Collider at CERN reports a constraint on lepton-flavour-violating effects in weak interactions, searching for Z -boson decays into a τ lepton and another lepton of different flavour with opposite electric charge. The branching fractions for these decays are measured to be less than 8.1 × 10 −6 ( e τ ) and 9.5 × 10 −6 ( μ τ ) at the 95% confidence level using 139 fb −1 of proton–proton collision data at a centre-of-mass energy of $$\\sqrt{s}=13\\,{\\rm{TeV}}$$ s = 13 TeV and 20.3 fb −1 at $$\\sqrt{s}=8\\,{\\rm{TeV}}.$$ s = 8 TeV . These results supersede the limits from the Large Electron–Positron Collider experiments conducted more than two decades ago.
Search for Dark Matter Produced in Association with a Dark Higgs Boson Decaying into
W ±
Publisher:
American Physical Society (APS)
Date:
26-03-2021
Publisher: American Physical Society (APS)
Date: 26-03-2021
Search for exotic decays of the Higgs boson into b$$ \overline{b} $$ and missing transverse momentum in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 2022
Abstract: A search for the exotic decay of the Higgs boson ( H ) into a b $$ \\overline{b} $$ b ¯ resonance plus missing transverse momentum is described. The search is performed with the ATLAS detector at the Large Hadron Collider using 139 fb − 1 of pp collisions at $$ \\sqrt{s} $$ s = 13 TeV. The search targets events from ZH production in an NMSSM scenario where H → $$ {\\overset{\\sim }{\\chi}}_2^0{\\overset{\\sim }{\\chi}}_1^0 $$ χ ~ 2 0 χ ~ 1 0 , with $$ {\\overset{\\sim }{\\chi}}_2^0 $$ χ ~ 2 0 → $$ a{\\overset{\\sim }{\\chi}}_1^0 $$ a χ ~ 1 0 , where a is a light pseudoscalar Higgs boson and $$ {\\overset{\\sim }{\\chi}}_{1,2}^0 $$ χ ~ 1 , 2 0 are the two lightest neutralinos. The decay of the a boson into a pair of b -quarks results in a peak in the dijet invariant mass distribution. The final-state signature consists of two leptons, two or more jets, at least one of which is identified as originating from a b -quark, and missing transverse momentum. Observations are consistent with Standard Model expectations and upper limits are set on the product of cross section times branching ratio for a three-dimensional scan of the masses of the $$ {\\overset{\\sim }{\\chi}}_2^0 $$ χ ~ 2 0 , $$ {\\overset{\\sim }{\\chi}}_1^0 $$ χ ~ 1 0 and a boson.
Measurements of W+W−+ ≥ 1 jet production cross-sections in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 06-2021
Abstract: Fiducial and differential cross-section measurements of W + W − production in association with at least one hadronic jet are presented. These measurements are sensitive to the properties of electroweak-boson self-interactions and provide a test of perturbative quantum chromodynamics and the electroweak theory. The analysis is performed using proton-proton collision data collected at $$ \sqrt{s} $$ s = 13 TeV with the ATLAS experiment, corresponding to an integrated luminosity of 139 fb − 1 . Events are selected with exactly one oppositely charged electron-muon pair and at least one hadronic jet with a transverse momentum of p T 30 GeV and a pseudorapidity of | η | 4 . 5. After subtracting the background contributions and correcting for detector effects, the jet-inclusive W + W − + ≥ 1 jet fiducial cross-section and W + W − + jets differential cross-sections with respect to several kinematic variables are measured. These measurements include leptonic quantities, such as the lepton transverse momenta and the transverse mass of the W + W − system, as well as jet-related observables such as the leading jet transverse momentum and the jet multiplicity. Limits on anomalous triple-gauge-boson couplings are obtained in a phase space where interference between the Standard Model litude and the anomalous litude is enhanced.
Inclusive and differential cross-sections for dilepton $$ t\overline{t} $$ production measured in $$ \sqrt{s} $$ = 13 TeV pp collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 17-07-2023
Abstract: Differential and double-differential distributions of kinematic variables of leptons from decays of top-quark pairs ( $$ t\\overline{t} $$ t t ¯ ) are measured using the full LHC Run 2 data s le collected with the ATLAS detector. The data were collected at a pp collision energy of $$ \\sqrt{s} $$ s = 13 TeV and correspond to an integrated luminosity of 140 fb − 1 . The measurements use events containing an oppositely charged eμ pair and b -tagged jets. The results are compared with predictions from several Monte Carlo generators. While no prediction is found to be consistent with all distributions, a better agreement with measurements of the lepton p T distributions is obtained by reweighting the $$ t\\overline{t} $$ t t ¯ s le so as to reproduce the top-quark p T distribution from an NNLO calculation. The inclusive top-quark pair production cross-section is measured as well, both in a fiducial region and in the full phase-space. The total inclusive cross-section is found to be $$ {\\sigma}_{t\\overline{t}}=829\\pm 1\\ \\left(\\textrm{stat}\\right)\\pm 13\\ \\left(\\textrm{syst}\\right)\\pm 8\\ \\left(\\textrm{lumi}\\right)\\pm 2\\ \\left(\\textrm{beam}\\right)\\ \\textrm{pb}, $$ σ t t ¯ = 829 ± 1 stat ± 13 syst ± 8 lumi ± 2 beam pb , where the uncertainties are due to statistics, systematic effects, the integrated luminosity and the beam energy. This is in excellent agreement with the theoretical expectation.
Search for new phenomena in final states with photons, jets and missing transverse momentum in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 03-07-2023
Abstract: A search for new phenomena has been performed in final states with at least one isolated high-momentum photon, jets and missing transverse momentum in proton–proton collisions at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV. The data, collected by the ATLAS experiment at the CERN LHC, correspond to an integrated luminosity of 139 fb − 1 . The experimental results are interpreted in a supersymmetric model in which pair-produced gluinos decay into neutralinos, which in turn decay into a gravitino, at least one photon, and jets. No significant deviations from the predictions of the Standard Model are observed. Upper limits are set on the visible cross section due to physics beyond the Standard Model, and lower limits are set on the masses of the gluinos and neutralinos, all at 95% confidence level. Visible cross sections greater than 0.022 fb are excluded and pair-produced gluinos with masses up to 2200 GeV are excluded for most of the NLSP masses investigated.
Measurement of the nuclear modification factor for muons from charm and bottom hadrons in Pb+Pb collisions at 5.02 TeV with the ATLAS detector
Publisher: Elsevier BV
Date: 06-2022
Constraints on Higgs boson production with large transverse momentum using
H →
Publisher:
American Physical Society (APS)
Date:
11-05-2022
Publisher: American Physical Society (APS)
Date: 11-05-2022
Medium-Induced Modification of
Z
Publisher:
American Physical Society (APS)
Date:
19-02-2021
Publisher: American Physical Society (APS)
Date: 19-02-2021
Search for long-lived charginos based on a disappearing-track signature using 136 fb$$^{-1}$$ of pp collisions at $$\sqrt{s}$$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 11-07-2022
DOI: 10.1140/EPJC/S10052-022-10489-5
Abstract: A search for long-lived charginos produced either directly or in the cascade decay of heavy prompt gluino states is presented. The search is based on proton–proton collision data collected at a centre-of-mass energy of $$\\sqrt{s}$$ s = 13 T $$\\text {eV}$$ eV between 2015 and 2018 with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 136 fb $$^{-1}$$ - 1 . Long-lived charginos are characterised by a distinct signature of a short and then disappearing track, and are reconstructed using at least four measurements in the ATLAS pixel detector, with no subsequent measurements in the silicon-microstrip tracking volume nor any associated energy deposits in the calorimeter. The final state is complemented by a large missing transverse-momentum requirement for triggering purposes and at least one high-transverse-momentum jet. No excess above the expected backgrounds is observed. Exclusion limits are set at 95% confidence level on the masses of the chargino and gluino for different chargino lifetimes. Chargino masses up to 660 (210) G $$\\text {eV}$$ eV are excluded in scenarios where the chargino is a pure wino (higgsino). For charginos produced during the cascade decay of a heavy gluino, gluinos with masses below 2.1 T $$\\text {eV}$$ eV are excluded for a chargino mass of 300 G $$\\text {eV}$$ eV and a lifetime of 0.2 ns.
Search for resonant pair production of Higgs bosons in the
b b
Publisher:
American Physical Society (APS)
Date:
11-05-2022
Publisher: American Physical Society (APS)
Date: 11-05-2022
Search for Higgs Boson Decays into a
Z
Publisher: American Physical Society (APS)
Date: 25-11-2020
C P
Publisher:
American Physical Society (APS)
Date:
05-08-2020
Publisher: American Physical Society (APS)
Date: 05-08-2020
Search for dark matter produced in association with a Higgs boson decaying to tau leptons at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 26-09-2023
Evidence for $$t\bar{t}t\bar{t}$$ production in the multilepton final state in proton–proton collisions at $$\sqrt{s}=13$$ $$\text {TeV}$$ with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 11-2020
DOI: 10.1140/EPJC/S10052-020-08509-3
Abstract: A search is presented for four-top-quark production using an integrated luminosity of 139 fb $$^{-1}$$ - 1 of proton–proton collision data at a centre-of-mass energy of $$13~\\text {TeV}$$ 13 TeV collected by the ATLAS detector at the LHC. Events are selected if they contain a same-sign lepton pair or at least three leptons (electrons or muons). Jet multiplicity, jet flavour and event kinematics are used to separate signal from the background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The four-top-quark production cross section is measured to be $$24^{+7}_{-6}$$ 24 - 6 + 7 fb. This corresponds to an observed (expected) significance with respect to the background-only hypothesis of 4.3 (2.4) standard deviations and provides evidence for this process.
Differential $$ t\overline{t} $$ cross-section measurements using boosted top quarks in the all-hadronic final state with 139 fb−1 of ATLAS data
Publisher: Springer Science and Business Media LLC
Date: 06-2021
Abstract: Measurements of single-, double-, and triple-differential cross-sections are presented for boosted top-quark pair-production in 13 TeV proton–proton collisions recorded by the ATLAS detector at the LHC. The top quarks are observed through their hadronic decay and reconstructed as large-radius jets with the leading jet having transverse momentum ( p T ) greater than 500 GeV. The observed data are unfolded to remove detector effects. The particle-level cross-section, multiplied by the $$ t\\overline{t}\\to WWb\\overline{b} $$ t t ¯ → WWb b ¯ branching fraction and measured in a fiducial phase space defined by requiring the leading and second-leading jets to have p T 500 GeV and p T 350 GeV, respectively, is 331 ± 3(stat.) ± 39(syst.) fb. This is approximately 20% lower than the prediction of $$ {398}_{-49}^{+48} $$ 398 − 49 + 48 fb by P owheg +P ythia 8 with next-to-leading-order (NLO) accuracy but consistent within the theoretical uncertainties. Results are also presented at the parton level, where the effects of top-quark decay, parton showering, and hadronization are removed such that they can be compared with fixed-order next-to-next-to-leading-order (NNLO) calculations. The parton-level cross-section, measured in a fiducial phase space similar to that at particle level, is 1 . 94 ± 0 . 02(stat.) ± 0 . 25(syst.) pb. This agrees with the NNLO prediction of $$ {1.96}_{-0.17}^{+0.02} $$ 1.96 − 0.17 + 0.02 pb. Reasonable agreement with the differential cross-sections is found for most NLO models, while the NNLO calculations are generally in better agreement with the data. The differential cross-sections are interpreted using a Standard Model effective field-theory formalism and limits are set on Wilson coefficients of several four-fermion operators.
Performance of the ATLAS RPC detector and Level-1 muon barrel trigger at √(s)=13 TeV
Publisher: IOP Publishing
Date: 07-2021
DOI: 10.1088/1748-0221/16/07/P07029
Abstract: The ATLAS experiment at the Large Hadron Collider (LHC) employs a trigger system consisting of a first-level hardware trigger (L1) and a software-based high-level trigger. The L1 muon trigger system selects muon candidates, assigns them to the correct LHC bunch crossing and classifies them into one of six transverse-momentum threshold classes. The L1 muon trigger system uses resistive-plate chambers (RPCs) to generate the muon-induced trigger signals in the central (barrel) region of the ATLAS detector. The ATLAS RPCs are arranged in six concentric layers and operate in a toroidal magnetic field with a bending power of 1.5 to 5.5 Tm. The RPC detector consists of about 3700 gas volumes with a total surface area of more than 4000 m 2 . This paper reports on the performance of the RPC detector and L1 muon barrel trigger using 60.8 fb -1 of proton-proton collision data recorded by the ATLAS experiment in 2018 at a centre-of-mass energy of 13 TeV. Detector and trigger performance are studied using Z boson decays into a muon pair. Measurements of the RPC detector response, efficiency, and time resolution are reported. Measurements of the L1 muon barrel trigger efficiencies and rates are presented, along with measurements of the properties of the selected s le of muon candidates. Measurements of the RPC currents, counting rates and mean avalanche charge are performed using zero-bias collisions. Finally, RPC detector response and efficiency are studied at different high voltage and front-end discriminator threshold settings in order to extrapolate detector response to the higher luminosity expected for the High Luminosity LHC.
Measurement of the production cross section of pairs of isolated photons in pp collisions at 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 11-2021
Abstract: A measurement of prompt photon-pair production in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV is presented. The data were recorded by the ATLAS detector at the LHC with an integrated luminosity of 139 fb − 1 . Events with two photons in the well-instrumented region of the detector are selected. The photons are required to be isolated and have a transverse momentum of $$ {p}_{\\mathrm{T}{,}_{\\gamma 1(2)}} $$ p T , γ 1 2 40 (30) GeV for the leading (sub-leading) photon. The differential cross sections as functions of several observables for the diphoton system are measured and compared with theoretical predictions from state-of-the-art Monte Carlo and fixed-order calculations. The QCD predictions from next-to-next-to-leading-order calculations and multi-leg merged calculations are able to describe the measured integrated and differential cross sections within uncertainties, whereas lower-order calculations show significant deviations, demonstrating that higher-order perturbative QCD corrections are crucial for this process. The resummed predictions with parton showers additionally provide an excellent description of the low transverse-momentum regime of the diphoton system.
Search for events with a pair of displaced vertices from long-lived neutral particles decaying into hadronic jets in the ATLAS muon spectrometer in
Publisher:
American Physical Society (APS)
Date:
09-08-2022
Publisher: American Physical Society (APS)
Date: 09-08-2022
Observation of
W W W
Publisher:
American Physical Society (APS)
Date:
04-08-2022
Publisher: American Physical Society (APS)
Date: 04-08-2022
Measurements of Higgs boson production by gluon-gluon fusion and vector-boson fusion using
H
Publisher:
American Physical Society (APS)
Date:
08-08-2023
Publisher: American Physical Society (APS)
Date: 08-08-2023
Measurements of jet observables sensitive to
b
Publisher:
American Physical Society (APS)
Date:
09-08-2022
Publisher: American Physical Society (APS)
Date: 09-08-2022
Observation of the
γ γ → τ
Publisher:
American Physical Society (APS)
Date:
31-01-2018
Publisher: American Physical Society (APS)
Date: 31-01-2018
Search for heavy neutral Higgs bosons produced in association with
b
Publisher: American Physical Society (APS)
Date: 13-08-2020
Search for new phenomena in final states with b-jets and missing transverse momentum in $$ \sqrt{\mathrm{s}} $$ = 13 TeV pp collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 05-2021
Abstract: The results of a search for new phenomena in final states with b -jets and missing transverse momentum using 139 fb − 1 of proton-proton data collected at a centre-of-mass energy $$ \\sqrt{s} $$ s = 13 TeV by the ATLAS detector at the LHC are reported. The analysis targets final states produced by the decay of a pair-produced supersymmetric bottom squark into a bottom quark and a stable neutralino. The analysis also seeks evidence for models of pair production of dark matter particles produced through the decay of a generic scalar or pseudoscalar mediator state in association with a pair of bottom quarks, and models of pair production of scalar third-generation down-type leptoquarks. No significant excess of events over the Standard Model background expectation is observed in any of the signal regions considered by the analysis. Bottom squark masses below 1270 GeV are excluded at 95% confidence level if the neutralino is massless. In the case of nearly mass-degenerate bottom squarks and neutralinos, the use of dedicated secondary-vertex identification techniques permits the exclusion of bottom squarks with masses up to 660 GeV for mass splittings between the squark and the neutralino of 10 GeV. These limits extend substantially beyond the regions of parameter space excluded by similar ATLAS searches performed previously.
Measurement of the $$ {B}_s^0 $$ → μμ effective lifetime with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 28-09-2202
Search for Higgs boson decays into two new low-mass spin-0 particles in the
4 b
Publisher:
American Physical Society (APS)
Date:
07-12-2020
Publisher: American Physical Society (APS)
Date: 07-12-2020
Search for resonances decaying into a weak vector boson and a Higgs boson in the fully hadronic final state produced in
Publisher:
American Physical Society (APS)
Date:
17-12-2020
Publisher: American Physical Society (APS)
Date: 17-12-2020
Erratum to: Measurement of light-by-light scattering and search for axion-like particles with 2.2 nb−1 of Pb+Pb data with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 11-2021
Search for long-lived, massive particles in events with a displaced vertex and a muon with large impact parameter in
Publisher: American Physical Society (APS)
Date: 14-08-2020
Search for a new heavy scalar particle decaying into a Higgs boson and a new scalar singlet in final states with one or two light leptons and a pair of τ-leptons with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 03-10-2023
Search for doubly and singly charged Higgs bosons decaying into vector bosons in multi-lepton final states with the ATLAS detector using proton-proton collisions at $$ \sqrt{\mathrm{s}} $$ = 13 TeV
Publisher: Springer Science and Business Media LLC
Date: 06-2021
Abstract: A search for charged Higgs bosons decaying into W ± W ± or W ± Z bosons is performed, involving experimental signatures with two leptons of the same charge, or three or four leptons with a variety of charge combinations, missing transverse momentum and jets. A data s le of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018 is used. The data correspond to a total integrated luminosity of 139 fb − 1 . The search is guided by a type-II seesaw model that extends the scalar sector of the Standard Model with a scalar triplet, leading to a phenomenology that includes doubly and singly charged Higgs bosons. Two scenarios are explored, corresponding to the pair production of doubly charged H ±± bosons, or the associated production of a doubly charged H ±± boson and a singly charged H ± boson. No significant deviations from the Standard Model predictions are observed. H ±± bosons are excluded at 95% confidence level up to 350 GeV and 230 GeV for the pair and associated production modes, respectively.
Search for Heavy Resonances Decaying into a Photon and a Hadronically Decaying Higgs Boson in
p p
Publisher:
American Physical Society (APS)
Date:
18-12-2020
Publisher: American Physical Society (APS)
Date: 18-12-2020
Search for charged Higgs bosons decaying into a top quark and a bottom quark at $$ \sqrt{\mathrm{s}} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 06-2021
Abstract: A search for charged Higgs bosons decaying into a top quark and a bottom quark is presented. The data analysed correspond to 139 fb − 1 of proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV, recorded with the ATLAS detector at the LHC. The production of a heavy charged Higgs boson in association with a top quark and a bottom quark, pp → tbH + → tbtb , is explored in the H + mass range from 200 to 2000 GeV using final states with jets and one electron or muon. Events are categorised according to the multiplicity of jets and b -tagged jets, and multivariate analysis techniques are used to discriminate between signal and background events. No significant excess above the background-only hypothesis is observed and exclusion limits are derived for the production cross-section times branching ratio of a charged Higgs boson as a function of its mass they range from 3.6 pb at 200 GeV to 0.036 pb at 2000 GeV at 95% confidence level. The results are interpreted in the hMSSM and $$ {M}_h^{125} $$ M h 125 scenarios.
Observation of Single-Top-Quark Production in Association with a Photon Using the ATLAS Detector
Publisher: American Physical Society (APS)
Date: 30-10-2023
Measurement of the nuclear modification factor of b-jets in 5.02 TeV Pb+Pb collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 25-05-2023
DOI: 10.1140/EPJC/S10052-023-11427-9
Abstract: This paper presents a measurement of b -jet production in Pb+Pb and pp collisions at $$\\sqrt{s_{_\\text {NN}}}=5.02$$ s NN = 5.02 TeV with the ATLAS detector at the LHC. The measurement uses 260 $$\\text {pb}^{-1}$$ pb - 1 of pp collisions collected in 2017 and 1.4 $$\\text {nb}^{-1}$$ nb - 1 of Pb+Pb collisions collected in 2018. In both collision systems, jets are reconstructed via the anti- $$k_{t}$$ k t algorithm. The b -jets are identified from a s le of jets containing muons from the semileptonic decay of b -quarks using template fits of the muon momentum relative to the jet axis. In pp collisions, b -jets are reconstructed for radius parameters $$R= 0.2$$ R = 0.2 and $$R= 0.4$$ R = 0.4 , and only $$R= 0.2$$ R = 0.2 jets are used in Pb+Pb collisions. For comparison, inclusive $$R= 0.2$$ R = 0.2 jets are also measured using 1.7 $$\\text {nb}^{-1}$$ nb - 1 of Pb+Pb collisions collected in 2018 and the same pp collision data as the b -jet measurement. The nuclear modification factor, $$R_\\text {AA}$$ R AA , is calculated for both b -jets and inclusive jets with $$R= 0.2$$ R = 0.2 over the transverse momentum range of 80–290 GeV. The nuclear modification factor for b -jets decreases from peripheral to central collisions. The ratio of the b -jet $$R_\\text {AA}$$ R AA to inclusive jet $$R_\\text {AA}$$ R AA is also presented and suggests that the $$R_\\text {AA}$$ R AA for b -jets is larger than that for inclusive jets in central Pb+Pb collisions. The measurements are compared with theoretical calculations and suggest a role for mass and colour-charge effects in partonic energy loss in heavy-ion collisions.
Constraints on spin-0 dark matter mediators and invisible Higgs decays using ATLAS 13 TeV pp collision data with two top quarks and missing transverse momentum in the final state
Publisher: Springer Science and Business Media LLC
Date: 13-06-2023
DOI: 10.1140/EPJC/S10052-023-11477-Z
Abstract: This paper presents a statistical combination of searches targeting final states with two top quarks and invisible particles, characterised by the presence of zero, one or two leptons, at least one jet originating from a b -quark and missing transverse momentum. The analyses are searches for phenomena beyond the Standard Model consistent with the direct production of dark matter in pp collisions at the LHC, using 139 fb $$^{-\\text {1}}$$ - 1 of data collected with the ATLAS detector at a centre-of-mass energy of 13 TeV. The results are interpreted in terms of simplified dark matter models with a spin-0 scalar or pseudoscalar mediator particle. In addition, the results are interpreted in terms of upper limits on the Higgs boson invisible branching ratio, where the Higgs boson is produced according to the Standard Model in association with a pair of top quarks. For scalar (pseudoscalar) dark matter models, with all couplings set to unity, the statistical combination extends the mass range excluded by the best of the in idual channels by 50 (25) GeV, excluding mediator masses up to 370 GeV. In addition, the statistical combination improves the expected coupling exclusion reach by 14% (24%), assuming a scalar (pseudoscalar) mediator mass of 10 GeV. An upper limit on the Higgs boson invisible branching ratio of 0.38 ( $$\\text {0.30}^{+\\text {0.13}}_{-\\text {0.09}}$$ 0.30 - 0.09 + 0.13 ) is observed (expected) at 95% confidence level.
Strong Constraints on Jet Quenching in Centrality-Dependent
p + Pb
Publisher: American Physical Society (APS)
Date: 16-08-2023
Measurements of top-quark pair single- and double-differential cross-sections in the all-hadronic channel in pp collisions at $$ \sqrt{\mathrm{s}} $$ = 13 TeV using the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 2021
Abstract: Differential cross-sections are measured for top-quark pair production in the all-hadronic decay mode, using proton-proton collision events collected by the ATLAS experiment in which all six decay jets are separately resolved. Absolute and normalised single- and double-differential cross-sections are measured at particle and parton level as a function of various kinematic variables. Emphasis is placed on well-measured observables in fully reconstructed final states, as well as on the study of correlations between the top-quark pair system and additional jet radiation identified in the event. The study is performed using data from proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV collected by the ATLAS detector at CERN’s Large Hadron Collider in 2015 and 2016, corresponding to an integrated luminosity of 36.1 fb − 1 . The rapidities of the in idual top quarks and of the top-quark pair are well modelled by several independent event generators. Significant mismodelling is observed in the transverse momenta of the leading three jet emissions, while the leading top-quark transverse momentum and top-quark pair transverse momentum are both found to be incompatible with several theoretical predictions.
Measurement of the t t
Publisher:
Elsevier BV
Date:
11-2020
Publisher: Elsevier BV
Date: 11-2020
Search for Higgs boson decays into a pair of pseudoscalar particles in the
b b μ
Publisher:
American Physical Society (APS)
Date:
11-01-2022
Publisher: American Physical Society (APS)
Date: 11-01-2022
Search for high-mass Wγ and Zγ resonances using hadronic W/Z boson decays from 139 fb−1 of pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 14-07-2023
Abstract: A search for high-mass charged and neutral bosons decaying to Wγ and Zγ final states is presented in this paper. The analysis uses a data s le of $$ \\sqrt{s} $$ s = 13 TeV proton-proton collisions with an integrated luminosity of 139 fb − 1 collected by the ATLAS detector during LHC Run 2 operation. The sensitivity of the search is determined using models of the production and decay of spin-1 charged bosons and spin-0/2 neutral bosons. The range of resonance masses explored extends from 1.0 TeV to 6.8 TeV. At these high resonance masses, it is beneficial to target the hadronic decays of the W and Z bosons because of their large branching fractions. The decay products of the high-momentum W/Z bosons are strongly collimated and boosted-boson tagging techniques are employed to improve the sensitivity. No evidence of a signal above the Standard Model backgrounds is observed, and upper limits on the production cross-sections of these bosons times their branching fractions to Wγ and Zγ are derived for various boson production models.
Measurements of differential cross-sections in top-quark pair events with a high transverse momentum top quark and limits on beyond the Standard Model contributions to top-quark pair production with t
Publisher: Springer Science and Business Media LLC
Date: 13-06-2022
Abstract: Cross-section measurements of top-quark pair production where the hadronically decaying top quark has transverse momentum greater than 355 GeV and the other top quark decays into ℓνb are presented using 139 fb − 1 of data collected by the ATLAS experiment during proton-proton collisions at the LHC. The fiducial cross-section at $$ \\sqrt{s} $$ s = 13 TeV is measured to be σ = 1 . 267 ± 0 . 005 ± 0 . 053 pb, where the uncertainties reflect the limited number of data events and the systematic uncertainties, giving a total uncertainty of 4 . 2%. The cross-section is measured differentially as a function of variables characterising the $$ t\\overline{t} $$ t t ¯ system and additional radiation in the events. The results are compared with various Monte Carlo generators, including comparisons where the generators are reweighted to match a parton-level calculation at next-to-next-to-leading order. The reweighting improves the agreement between data and theory. The measured distribution of the top-quark transverse momentum is used to search for new physics in the context of the effective field theory framework. No significant deviation from the Standard Model is observed and limits are set on the Wilson coefficients of the dimension-six operators O tG and $$ {O}_{tq}^{(8)} $$ O tq 8 , where the limits on the latter are the most stringent to date.
Search for heavy particles in the
b
Publisher:
American Physical Society (APS)
Date:
07-01-2022
Publisher: American Physical Society (APS)
Date: 07-01-2022
Search for leptoquarks decaying into the bτ final state in pp collisions at $$ \sqrt{\textrm{s}} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 02-10-2023
Measurements of the production cross-section for a Z boson in association with b-jets in proton-proton collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 07-2020
Abstract: This paper presents a measurement of the production cross-section of a Z boson in association with b -jets, in proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV with the ATLAS experiment at the Large Hadron Collider using data corresponding to an integrated luminosity of 35.6 fb − 1 . Inclusive and differential cross-sections are measured for events containing a Z boson decaying into electrons or muons and produced in association with at least one or at least two b -jets with transverse momentum p T 20 GeV and rapidity |y| 2 . 5. Predictions from several Monte Carlo generators based on leading-order (LO) or next-to-leading-order (NLO) matrix elements interfaced with a parton-shower simulation and testing different flavour schemes for the choice of initial-state partons are compared with measured cross-sections. The 5-flavour number scheme predictions at NLO accuracy agree better with data than 4-flavour number scheme ones. The 4-flavour number scheme predictions underestimate data in events with at least one b-jet.
Search for new phenomena in final states with large jet multiplicities and missing transverse momentum using $$ \sqrt{s} $$ = 13 TeV proton-proton collisions recorded by ATLAS in Run 2 of the LHC
Publisher: Springer Science and Business Media LLC
Date: 10-2020
Abstract: Results of a search for new particles decaying into eight or more jets and moderate missing transverse momentum are presented. The analysis uses 139 fb − 1 of proton-proton collision data at $$ \\sqrt{s} $$ s = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider between 2015 and 2018. The selection rejects events containing isolated electrons or muons, and makes requirements according to the number of b -tagged jets and the scalar sum of masses of large-radius jets. The search extends previous analyses both in using a larger dataset and by employing improved jet and missing transverse momentum reconstruction methods which more cleanly separate signal from background processes. No evidence for physics beyond the Standard Model is found. The results are interpreted in the context of supersymmetry-inspired simplified models, significantly extending the limits on the gluino mass in those models. In particular, limits on the gluino mass are set at 2 TeV when the lightest neutralino is nearly massless in a model assuming a two-step cascade decay via the lightest chargino and second-lightest neutralino.
Search for $$ t\overline{t} $$ resonances in fully hadronic final states in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 10-2020
Abstract: This paper presents a search for new heavy particles decaying into a pair of top quarks using 139 fb − 1 of proton-proton collision data recorded at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV with the ATLAS detector at the Large Hadron Collider. The search is performed using events consistent with pair production of high-transverse-momentum top quarks and their subsequent decays into the fully hadronic final states. The analysis is optimized for resonances decaying into a $$ t\\overline{t} $$ t t ¯ pair with mass above 1.4 TeV, exploiting a dedicated multivariate technique with jet substructure to identify hadronically decaying top quarks using large-radius jets and evaluating the background expectation from data. No significant deviation from the background prediction is observed. Limits are set on the production cross-section times branching fraction for the new Z ′ boson in a topcolor-assisted-technicolor model. The Z ′ boson masses below 3.9 and 4.7 TeV are excluded at 95% confidence level for the decay widths of 1% and 3%, respectively.
Study of $$ {\mathrm{B}}_{\mathrm{c}}^{+}\to \mathrm{J}/\psi {\mathrm{D}}_{\mathrm{s}}^{+} $$ and $$ {\mathrm{B}}_{\mathrm{c}}^{+}\to \mathrm{J}/\psi {\mathrm{D}}_{\mathrm{s}}^{\ast +} $$ decays in pp
Publisher: Springer Science and Business Media LLC
Date: 05-08-2022
Abstract: A study of $$ {B}_c^{+}\\to J/\\psi {D}_s^{+} $$ B c + → J / ψ D s + and $$ {B}_c^{+}\\to J/\\psi {D}_s^{\\ast +} $$ B c + → J / ψ D s ∗ + decays using 139 fb − 1 of integrated luminosity collected with the ATLAS detector from $$ \\sqrt{s} $$ s = 13 TeV pp collisions at the LHC is presented. The ratios of the branching fractions of the two decays to the branching fraction of the $$ {B}_c^{+} $$ B c + → J/ψπ + decay are measured: $$ \\mathcal{B}\\left({B}_c^{+}\\to J/\\psi {D}_s^{+}\\right)/\\mathcal{B}\\left({B}_c^{+}\\to J/{\\psi \\pi}^{+}\\right) $$ B B c + → J / ψ D s + / B B c + → J / ψπ + = 2 . 76 ± 0 . 47 and $$ \\mathcal{B}\\left({B}_c^{+}\\to J/\\psi {D}_s^{\\ast +}\\right)/\\mathcal{B}\\left({B}_c^{+}\\to J/{\\psi \\pi}^{+}\\right) $$ B B c + → J / ψ D s ∗ + / B B c + → J / ψπ + = 5 . 33 ± 0 . 96. The ratio of the branching fractions of the two decays is found to be $$ \\mathcal{B}\\left({B}_c^{+}\\to J/\\psi {D}_s^{\\ast +}\\right)/\\mathcal{B}\\left({B}_c^{+}\\to J/\\psi {D}_s^{\\ast +}\\right) $$ B B c + → J / ψ D s ∗ + / B B c + → J / ψ D s ∗ + = 1 . 93 ± 0 . 26. For the $$ {B}_c^{+}\\to J/\\psi {D}_s^{\\ast +} $$ B c + → J / ψ D s ∗ + decay, the transverse polarization fraction, Γ ±± / Γ, is measured to be 0 . 70 ± 0 . 11. The reported uncertainties include both the statistical and systematic components added in quadrature. The precision of the measurements exceeds that in all previous studies of these decays. These results supersede those obtained in the earlier ATLAS study of the same decays with $$ \\sqrt{s} $$ s = 7 and 8 TeV pp collision data. A comparison with available theoretical predictions for the measured quantities is presented.
Modelling and computational improvements to the simulation of single vector-boson plus jet processes for the ATLAS experiment
Publisher: Springer Science and Business Media LLC
Date: 05-08-2022
Abstract: This paper presents updated Monte Carlo configurations used to model the production of single electroweak vector bosons ( W , Z/γ ∗ ) in association with jets in proton-proton collisions for the ATLAS experiment at the Large Hadron Collider. Improvements pertaining to the electroweak input scheme, parton-shower splitting kernels and scale-setting scheme are shown for multi-jet merged configurations accurate to next-to-leading order in the strong and electroweak couplings. The computational resources required for these set-ups are assessed, and approximations are introduced resulting in a factor three reduction of the per-event CPU time without affecting the physics modelling performance. Continuous statistical enhancement techniques are introduced by ATLAS in order to populate low cross-section regions of phase space and are shown to match or exceed the generated effective luminosity. This, together with the lower per-event CPU time, results in a 50% reduction in the required computing resources compared to a legacy set-up previously used by the ATLAS collaboration. The set-ups described in this paper will be used for future ATLAS analyses and lay the foundation for the next generation of Monte Carlo predictions for single vector-boson plus jets production.
The ATLAS Fast TracKer system
Publisher: IOP Publishing
Date: 07-2021
DOI: 10.1088/1748-0221/16/07/P07006
Abstract: The ATLAS Fast TracKer (FTK) was designed to provide full tracking for the ATLAS high-level trigger by using pattern recognition based on Associative Memory (AM) chips and fitting in high-speed field programmable gate arrays. The tracks found by the FTK are based on inputs from all modules of the pixel and silicon microstrip trackers. The as-built FTK system and components are described, as is the online software used to control them while running in the ATLAS data acquisition system. Also described is the simulation of the FTK hardware and the optimization of the AM pattern banks. An optimization for long-lived particles with large impact parameter values is included. A test of the FTK system with the data playback facility that allowed the FTK to be commissioned during the shutdown between Run 2 and Run 3 of the LHC is reported. The resulting tracks from part of the FTK system covering a limited η–ϕ region of the detector are compared with the output from the FTK simulation. It is shown that FTK performance is in good agreement with the simulation.
Search for new phenomena in three- or four-lepton events in pp collisions at s
Publisher:
Elsevier BV
Date:
2022
Publisher: Elsevier BV
Date: 2022
Operation and performance of the ATLAS semiconductor tracker in LHC Run 2
Publisher: IOP Publishing
Date: 2022
DOI: 10.1088/1748-0221/17/01/P01013
Abstract: The semiconductor tracker (SCT) is one of the tracking systems for charged particles in the ATLAS detector. It consists of 4088 silicon strip sensor modules. During Run 2 (2015–2018) the Large Hadron Collider delivered an integrated luminosity of 156 fb -1 to the ATLAS experiment at a centre-of-mass proton-proton collision energy of 13 TeV. The instantaneous luminosity and pile-up conditions were far in excess of those assumed in the original design of the SCT detector. Due to improvements to the data acquisition system, the SCT operated stably throughout Run 2. It was available for 99.9% of the integrated luminosity and achieved a data-quality efficiency of 99.85%. Detailed studies have been made of the leakage current in SCT modules and the evolution of the full depletion voltage, which are used to study the impact of radiation damage to the modules.
Engaging with Transformative Paradigms in Mental Health
Publisher: MDPI AG
Date: 09-09-2021
Abstract: When graduates of Australian social work courses embark on a career in mental health, the systems they enter are complex, fragmented and evolving. Emerging practitioners will commonly be confronted by the loneliness, social exclusion, poverty and prejudice experienced by people living with mental distress however, social work practice may not be focused on these factors. Instead, in accordance with the dominant biomedical perspective, symptom and risk management may predominate. Frustration with the limitations evident in this approach has seen the United Nations call for the transformation of mental health service delivery. Recognising paradigmatic influences on mental health social work may lead to a more considered enactment of person centred, recovery and rights-based approaches. This paper compares and contrasts influences of neo-liberalism, critical theory, human rights and post-structuralism on mental health social work practice. In preparing social work practitioners to recognise the influence of, and work more creatively with, intersecting paradigms, social work educators strive to foster a transformative approach to mental health practice that straddles discourses.
Search for an axion-like particle with forward proton scattering in association with photon pairs at ATLAS
Publisher: Springer Science and Business Media LLC
Date: 31-07-2023
Abstract: A search for forward proton scattering in association with light-by-light scattering mediated by an axion-like particle is presented, using the ATLAS Forward Proton spectrometer to detect scattered protons and the central ATLAS detector to detect pairs of outgoing photons. Proton-proton collision data recorded in 2017 at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV were analysed, corresponding to an integrated luminosity of 14.6 fb − 1 . A total of 441 candidate events were selected. A search was made for a narrow resonance in the diphoton mass distribution, corresponding to an axion-like particle (ALP) with mass in the range 150–1600 GeV. No excess is observed above a smooth background. Upper limits on the production cross section of a narrow resonance are set as a function of the mass, and are interpreted as upper limits on the ALP production coupling constant, assuming 100% decay branching ratio into a photon pair. The inferred upper limit on the coupling constant is in the range 0.04–0.09 TeV − 1 at 95% confidence level.
Search for third-generation vector-like leptons in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 13-07-2023
Abstract: A search for vector-like leptons in multilepton (two, three, or four-or-more electrons plus muons) final states with zero or more hadronic τ -lepton decays is presented. The search is performed using a dataset corresponding to an integrated luminosity of 139 fb − 1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the LHC. To maximize the separation of signal and background, a machine-learning classifier is used. No excess of events is observed beyond the Standard Model expectation. Using a doublet vector-like lepton model, vector-like leptons coupling to third-generation Standard Model leptons are excluded in the mass range from 130 GeV to 900 GeV at the 95% confidence level, while the highest excluded mass is expected to be 970 GeV.
Measurements of the Higgs boson inclusive and differential fiducial cross sections in the 4$$\ell $$ decay channel at $$\sqrt{s}$$ = 13 TeV
Publisher: Springer Science and Business Media LLC
Date: 10-2020
DOI: 10.1140/EPJC/S10052-020-8223-0
Abstract: Inclusive and differential fiducial cross sections of the Higgs boson are measured in the $$H \\rightarrow ZZ^{*} \\rightarrow 4\\ell $$ H → Z Z ∗ → 4 ℓ ( $$\\ell = e,\\mu $$ ℓ = e , μ ) decay channel. The results are based on proton-proton collision data produced at the Large Hadron Collider at a centre-of-mass energy of 13 TeV and recorded by the ATLAS detector from 2015 to 2018, equivalent to an integrated luminosity of 139 $$\\hbox {fb}^{-1}$$ fb - 1 . The inclusive fiducial cross section for the $$H \\rightarrow ZZ^{*} \\rightarrow 4\\ell $$ H → Z Z ∗ → 4 ℓ process is measured to be $$\\sigma _\\mathrm {fid} = 3.28 \\,{\\pm }\\, 0.32$$ σ fid = 3.28 ± 0.32 fb, in agreement with the Standard Model prediction of $$\\sigma _\\mathrm {fid, SM} = 3.41 \\pm 0.18 $$ σ fid , SM = 3.41 ± 0.18 fb. Differential fiducial cross sections are measured for a variety of observables which are sensitive to the production and decay of the Higgs boson. All measurements are in agreement with the Standard Model predictions. The results are used to constrain anomalous Higgs boson interactions with Standard Model particles.
Measurement of the polarisation of W bosons produced in top-quark decays using dilepton events at
Publisher:
Elsevier BV
Date:
08-2023
Publisher: Elsevier BV
Date: 08-2023
Direct constraint on the Higgs–charm coupling from a search for Higgs boson decays into charm quarks with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 18-08-2022
DOI: 10.1140/EPJC/S10052-022-10588-3
Abstract: A search for the Higgs boson decaying into a pair of charm quarks is presented. The analysis uses proton–proton collisions to target the production of a Higgs boson in association with a leptonically decaying W or Z boson. The dataset delivered by the LHC at a centre-of-mass energy of "Equation missing" and recorded by the ATLAS detector corresponds to an integrated luminosity of 139 $$\text{ fb}^{-1}$$ fb - 1 . Flavour-tagging algorithms are used to identify jets originating from the hadronisation of charm quarks. The analysis method is validated with the simultaneous measurement of WW , WZ and ZZ production, with observed (expected) significances of 2.6 (2.2) standard deviations above the background-only prediction for the $$(W/Z)Z(\rightarrow c{\bar{c}})$$ ( W / Z ) Z ( → c c ¯ ) process and 3.8 (4.6) standard deviations for the $$(W/Z)W(\rightarrow cq)$$ ( W / Z ) W ( → c q ) process. The $$(W/Z)H(\rightarrow c {\bar{c}})$$ ( W / Z ) H ( → c c ¯ ) search yields an observed (expected) upper limit of 26 (31) times the predicted Standard Model cross-section times branching fraction for a Higgs boson with a mass of "Equation missing" , corresponding to an observed (expected) constraint on the charm Yukawa coupling modifier $$|\kappa _c| 8.5~(12.4)$$ | κ c | 8.5 ( 12.4 ) , at the 95% confidence level. A combination with the ATLAS $$(W/Z)H, H\rightarrow b{\bar{b}}$$ ( W / Z ) H , H → b b ¯ analysis is performed, allowing the ratio $$\kappa _c / \kappa _b$$ κ c / κ b to be constrained to less than 4.5 at the 95% confidence level, smaller than the ratio of the b- and c-quark masses, and therefore determines the Higgs-charm coupling to be weaker than the Higgs-bottom coupling at the 95% confidence level.
Search for neutral long-lived particles in pp collisions at $$ \sqrt{s} $$ = 13 TeV that decay into displaced hadronic jets in the ATLAS calorimeter
Publisher: Springer Science and Business Media LLC
Date: 06-2022
Abstract: A search for decays of pair-produced neutral long-lived particles (LLPs) is presented using 139 fb − 1 of proton-proton collision data collected by the ATLAS detector at the LHC in 2015–2018 at a centre-of-mass energy of 13 TeV. Dedicated techniques were developed for the reconstruction of displaced jets produced by LLPs decaying hadronically in the ATLAS hadronic calorimeter. Two search regions are defined for different LLP kinematic regimes. The observed numbers of events are consistent with the expected background, and limits for several benchmark signals are determined. For a SM Higgs boson with a mass of 125 GeV, branching ratios above 10% are excluded at 95% confidence level for values of c times LLP mean proper lifetime in the range between 20 mm and 10 m depending on the model. Upper limits are also set on the cross-section times branching ratio for scalars with a mass of 60 GeV and for masses between 200 GeV and 1 TeV.
Observation of electroweak production of two jets and a Z-boson pair
Publisher: Springer Science and Business Media LLC
Date: 09-02-2023
Search for Higgs bosons decaying into new spin-0 or spin-1 particles in four-lepton final states with the ATLAS detector with 139 fb−1 of pp collision data at $$ \sqrt{s} $$ = 13 TeV
Publisher: Springer Science and Business Media LLC
Date: 03-2022
Abstract: Searches are conducted for new spin-0 or spin-1 bosons using events where a Higgs boson with mass 125 GeV decays into four leptons ( ℓ = e , μ ). This decay is presumed to occur via an intermediate state which contains two on-shell, promptly decaying bosons: H → XX/ZX → 4 ℓ , where the new boson X has a mass between 1 and 60 GeV. The search uses pp collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 139 fb − 1 at a centre-of-mass energy $$ \\sqrt{s} $$ s = 13 TeV. The data are found to be consistent with Standard Model expectations. Limits are set on fiducial cross sections and on the branching ratio of the Higgs boson to decay into XX/ZX , improving those from previous publications by a factor between two and four. Limits are also set on mixing parameters relevant in extensions of the Standard Model containing a dark sector where X is interpreted to be a dark boson.
Dijet Resonance Search with Weak Supervision Using
s
Publisher:
American Physical Society (APS)
Date:
21-09-2020
Publisher: American Physical Society (APS)
Date: 21-09-2020
Search for a scalar partner of the top quark in the all-hadronic $$t{\bar{t}}$$ plus missing transverse momentum final state at $$\sqrt{s}=13$$ TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 08-2020
DOI: 10.1140/EPJC/S10052-020-8102-8
Abstract: A search for direct pair production of scalar partners of the top quark (top squarks or scalar third-generation up-type leptoquarks) in the all-hadronic $$t{\\bar{t}}$$ t t ¯ plus missing transverse momentum final state is presented. The analysis of 139 $$\\hbox {fb}^{-1}$$ fb - 1 of $${\\sqrt{s}=13}$$ s = 13 TeV proton–proton collision data collected using the ATLAS detector at the LHC yields no significant excess over the Standard Model background expectation. To interpret the results, a supersymmetric model is used where the top squark decays via $${\\tilde{t}} \\rightarrow t^{(*)} {\\tilde{\\chi }}^0_1$$ t ~ → t ( ∗ ) χ ~ 1 0 , with $$t^{(*)}$$ t ( ∗ ) denoting an on-shell (off-shell) top quark and $${\\tilde{\\chi }}^0_1$$ χ ~ 1 0 the lightest neutralino. Three specific event selections are optimised for the following scenarios. In the scenario where $$m_{{\\tilde{t}}} m_t+m_{{\\tilde{\\chi }}^0_1}$$ m t ~ m t + m χ ~ 1 0 , top squark masses are excluded in the range 400–1250 GeV for $${\\tilde{\\chi }}^0_1$$ χ ~ 1 0 masses below 200 GeV at 95% confidence level. In the situation where $$m_{{\\tilde{t}}}\\sim m_t+m_{{\\tilde{\\chi }}^0_1}$$ m t ~ ∼ m t + m χ ~ 1 0 , top squark masses in the range 300–630 GeV are excluded, while in the case where $$m_{{\\tilde{t}}} m_W+m_b+m_{{\\tilde{\\chi }}^0_1}$$ m t ~ m W + m b + m χ ~ 1 0 (with $$m_{{\\tilde{t}}}-m_{{\\tilde{\\chi }}^0_1}\\ge 5$$ m t ~ - m χ ~ 1 0 ≥ 5 GeV), considered for the first time in an ATLAS all-hadronic search, top squark masses in the range 300–660 GeV are excluded. Limits are also set for scalar third-generation up-type leptoquarks, excluding leptoquarks with masses below 1240 GeV when considering only leptoquark decays into a top quark and a neutrino.
Search for Displaced Leptons in
s = 13
Publisher:
American Physical Society (APS)
Date:
27-07-2021
Publisher: American Physical Society (APS)
Date: 27-07-2021
Search for direct production of electroweakinos in final states with missing transverse momentum and a Higgs boson decaying into photons in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS dete
Publisher: Springer Science and Business Media LLC
Date: 10-2020
Abstract: A search for a chargino-neutralino pair decaying via the 125 GeV Higgs boson into photons is presented. The study is based on the data collected between 2015 and 2018 with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 139 fb − 1 of pp collisions at a centre-of-mass energy of 13 TeV. No significant excess over the expected background is observed. Upper limits at 95% confidence level for a massless $$ {\\tilde{\\chi}}_1^0 $$ χ ˜ 1 0 are set on several electroweakino production cross-sections and the visible cross-section for beyond the Standard Model processes. In the context of simplified supersymmetric models, 95% confidence-level limits of up to 310 GeV in $$ m\\left({\\tilde{\\chi}}_1^{\\pm }/{\\tilde{\\chi}}_2^0\\right) $$ m χ ˜ 1 ± / χ ˜ 2 0 , where $$ m\\left({\\tilde{\\chi}}_1^0\\right) $$ m χ ˜ 1 0 = 0 . 5 GeV, are set. Limits at 95% confidence level are also set on the $$ {\\tilde{\\chi}}_1^{\\pm }{\\tilde{\\chi}}_2^0 $$ χ ˜ 1 ± χ ˜ 2 0 cross-section in the mass plane of $$ m\\left({\\tilde{\\chi}}_1^{\\pm }/{\\tilde{\\chi}}_2^0\\right) $$ m χ ˜ 1 ± / χ ˜ 2 0 and $$ m\\left({\\tilde{\\chi}}_1^0\\right) $$ m χ ˜ 1 0 , and on scenarios with gravitino as the lightest supersymmetric particle. Upper limits at the 95% confidence-level are set on the higgsino production cross-section. Higgsino masses below 380 GeV are excluded for the case of the higgsino fully decaying into a Higgs boson and a gravitino.
Measurements of azimuthal anisotropies of jet production in
Pb +
Publisher:
American Physical Society (APS)
Date:
07-06-2022
Publisher: American Physical Society (APS)
Date: 07-06-2022
Studies of the muon momentum calibration and performance of the ATLAS detector with pp collisions at $$\sqrt{s}=13$$ TeV
Publisher: Springer Science and Business Media LLC
Date: 08-2023
DOI: 10.1140/EPJC/S10052-023-11584-X
Abstract: This paper presents the muon momentum calibration and performance studies for the ATLAS detector based on the pp collisions data s le produced at $$\\sqrt{s}$$ s = 13 TeV at the LHC during Run 2 and corresponding to an integrated luminosity of 139 $${\\textrm{fb}}^{-1}$$ fb - 1 . An innovative approach is used to correct for potential charge-dependent momentum biases related to the knowledge of the detector geometry, using the $$Z\\rightarrow \\mu ^{+}\\mu ^{-}$$ Z → μ + μ - resonance. The muon momentum scale and resolution are measured using s les of $$J/\\psi \\rightarrow \\mu ^{+}\\mu ^{-}$$ J / ψ → μ + μ - and $$Z\\rightarrow \\mu ^{+}\\mu ^{-}$$ Z → μ + μ - events. A calibration procedure is defined and applied to simulated data to match the performance measured in real data. The calibration is validated using an independent s le of $$\\Upsilon \\rightarrow \\mu ^{+}\\mu ^{-}$$ Υ → μ + μ - events. At the Z $$(J/\\psi )$$ ( J / ψ ) peak, the momentum scale is measured with an uncertainty at the 0.05% (0.1%) level, and the resolution is measured with an uncertainty at the 1.5% (2%) level. The charge-dependent bias is removed with a dedicated in situ correction for momenta up to 450 GeV with a precision better than 0.03 $${\\textrm{TeV}}^{-1}$$ TeV - 1 .
Search for dark matter in association with an energetic photon in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 02-2021
Abstract: A search for dark matter is conducted in final states containing a photon and missing transverse momentum in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV. The data, collected during 2015–2018 by the ATLAS experiment at the CERN LHC, correspond to an integrated luminosity of 139 fb − 1 . No deviations from the predictions of the Standard Model are observed and 95% confidence-level upper limits between 2.45 fb and 0.5 fb are set on the visible cross section for contributions from physics beyond the Standard Model, in different ranges of the missing transverse momentum. The results are interpreted as 95% confidence-level limits in models where weakly interacting dark-matter candidates are pair-produced via an s -channel axial-vector or vector mediator. Dark-matter candidates with masses up to 415 (580) GeV are excluded for axial-vector (vector) mediators, while the maximum excluded mass of the mediator is 1460 (1470) GeV. In addition, the results are expressed in terms of 95% confidence-level limits on the parameters of a model with an axion-like particle produced in association with a photon, and are used to constrain the coupling g a Z γ of an axion-like particle to the electroweak gauge bosons.
Measurements of the suppression and correlations of dijets in Xe+Xe collisions at
s <
Publisher: American Physical Society (APS)
Date: 09-08-2023
Measurement of b-quark fragmentation properties in jets using the decay B± → J/ψK± in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 12-2021
Abstract: The fragmentation properties of jets containing b -hadrons are studied using charged B mesons in 139 fb − 1 of pp collisions at $$ \\sqrt{s} $$ s = 13 TeV, recorded with the ATLAS detector at the LHC during the period from 2015 to 2018. The B mesons are reconstructed using the decay of B ± into J/ψK ± , with the J/ψ decaying into a pair of muons. Jets are reconstructed using the anti- k t algorithm with radius parameter R = 0 . 4. The measurement determines the longitudinal and transverse momentum profiles of the reconstructed B hadrons with respect to the axes of the jets to which they are geometrically associated. These distributions are measured in intervals of the jet transverse momentum, ranging from 50 GeV to above 100 GeV. The results are corrected for detector effects and compared with several Monte Carlo predictions using different parton shower and hadronisation models. The results for the longitudinal and transverse profiles provide useful inputs to improve the description of heavy-flavour fragmentation in jets.
Search for Majorana neutrinos in same-sign WW scattering events from pp collisions at $$\sqrt{s}=13$$ TeV
Publisher: Springer Science and Business Media LLC
Date: 23-01-2118
Measurement of the energy asymmetry in $$t{\bar{t}}j$$ production at $$13\,$$TeV with the ATLAS experiment and interpretation in the SMEFT framework
Publisher: Springer Science and Business Media LLC
Date: 04-2022
DOI: 10.1140/EPJC/S10052-022-10101-W
Abstract: A measurement of the energy asymmetry in jet-associated top-quark pair production is presented using $$139\\,{\\mathrm {fb}}^{-1}$$ 139 fb - 1 of data collected by the ATLAS detector at the Large Hadron Collider during pp collisions at $$\\sqrt{s}=13\\,\\text {TeV}$$ s = 13 TeV . The observable measures the different probability of top and antitop quarks to have the higher energy as a function of the jet scattering angle with respect to the beam axis. The energy asymmetry is measured in the semileptonic $$t{\\bar{t}}$$ t t ¯ decay channel, and the hadronically decaying top quark must have transverse momentum above $$350\\,\\text {GeV}$$ 350 GeV . The results are corrected for detector effects to particle level in three bins of the scattering angle of the associated jet. The measurement agrees with the SM prediction at next-to-leading-order accuracy in quantum chromodynamics in all three bins. In the bin with the largest expected asymmetry, where the jet is emitted perpendicular to the beam, the energy asymmetry is measured to be $$-0.043\\pm 0.020$$ - 0.043 ± 0.020 , in agreement with the SM prediction of $$-0.037\\pm 0.003$$ - 0.037 ± 0.003 . Interpreting this result in the framework of the Standard Model effective field theory (SMEFT), it is shown that the energy asymmetry is sensitive to the top-quark chirality in four-quark operators and is therefore a valuable new observable in global SMEFT fits.
Measurement of hadronic event shapes in high-pT multijet final states at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 2021
Abstract: A measurement of event-shape variables in proton-proton collisions at large momentum transfer is presented using data collected at $$ \\sqrt{s} $$ s = 13 TeV with the ATLAS detector at the Large Hadron Collider. Six event-shape variables calculated using hadronic jets are studied in inclusive multijet events using data corresponding to an integrated luminosity of 139 fb − 1 . Measurements are performed in bins of jet multiplicity and in different ranges of the scalar sum of the transverse momenta of the two leading jets, reaching scales beyond 2 TeV. These measurements are compared with predictions from Monte Carlo event generators containing leading-order or next-to-leading order matrix elements matched to parton showers simulated to leading-logarithm accuracy. At low jet multiplicities, shape discrepancies between the measurements and the Monte Carlo predictions are observed. At high jet multiplicities, the shapes are better described but discrepancies in the normalisation are observed.
Constraints on Higgs boson properties using $$WW^{*}(\rightarrow e\nu \mu \nu )jj$$ production in $$36.1\,\mathrm{fb}^{-1}$$ of $$\sqrt{s}=13$$ TeV pp collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 18-07-2022
DOI: 10.1140/EPJC/S10052-022-10366-1
Abstract: This article presents the results of two studies of Higgs boson properties using the $$WW^*(\\rightarrow e\\nu \\mu \\nu )jj$$ W W ∗ ( → e ν μ ν ) j j final state, based on a dataset corresponding to $${36.1}{{\\mathrm{fb}}^{-1}}$$ 36.1 fb - 1 of $$\\sqrt{s}=13$$ s = 13 TeV proton–proton collisions recorded by the ATLAS experiment at the Large Hadron Collider. The first study targets Higgs boson production via gluon–gluon fusion and constrains the CP properties of the effective Higgs–gluon interaction. Using angular distributions and the overall rate, a value of $$\\tan (\\alpha ) = 0.0 \\pm 0.4 (\\mathrm {stat.}) \\pm 0.3 (\\mathrm {syst.})$$ tan ( α ) = 0.0 ± 0.4 ( stat . ) ± 0.3 ( syst . ) is obtained for the tangent of the mixing angle for CP-even and CP-odd contributions. The second study exploits the vector-boson fusion production mechanism to probe the Higgs boson couplings to longitudinally and transversely polarised W and Z bosons in both the production and the decay of the Higgs boson these couplings have not been directly constrained previously. The polarisation-dependent coupling-strength scale factors are defined as the ratios of the measured polarisation-dependent coupling strengths to those predicted by the Standard Model, and are determined using rate and kinematic information to be $$a_\\mathrm {L}=0.91^{+0.10}_{-0.18}$$ a L = 0 . 91 - 0.18 + 0.10 (stat.) $$^{+0.09}_{-0.17}$$ - 0.17 + 0.09 (syst.) and $$a_{\\mathrm {T}}=1.2 \\pm 0.4 $$ a T = 1.2 ± 0.4 (stat.) $$ ^{+0.2}_{-0.3} $$ - 0.3 + 0.2 (syst.). These coupling strengths are translated into pseudo-observables, resulting in $$\\kappa _{VV}= 0.91^{+0.10}_{-0.18}$$ κ VV = 0 . 91 - 0.18 + 0.10 (stat.) $$^{+0.09}_{-0.17}$$ - 0.17 + 0.09 (syst.) and $$\\epsilon _{VV} =0.13^{+0.28}_{-0.20}$$ ϵ VV = 0 . 13 - 0.20 + 0.28 (stat.) $$^{+0.08}_{-0.10}$$ - 0.10 + 0.08 (syst.). All results are consistent with the Standard Model predictions.
Measurement of the total cross section and $$\rho $$-parameter from elastic scattering in pp collisions at $$\sqrt{s}=13$$ TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 26-05-2023
DOI: 10.1140/EPJC/S10052-023-11436-8
Abstract: In a special run of the LHC with $$\\beta ^{\\star } = 2.5$$ β ⋆ = 2.5 km, proton–proton elastic-scattering events were recorded at $$\\sqrt{s} = 13$$ s = 13 TeV with an integrated luminosity of $$340~\\upmu {\\text {b}}^{-1}$$ 340 μ b - 1 using the ALFA subdetector of ATLAS in 2016. The elastic cross section was measured differentially in the Mandelstam t variable in the range from $$-t = 2.5 \\cdot 10^{-4}$$ - t = 2.5 · 10 - 4 GeV $$^{2}$$ 2 to $$-t = 0.46$$ - t = 0.46 GeV $$^{2}$$ 2 using 6.9 million elastic-scattering candidates. This paper presents measurements of the total cross section $$\\sigma _{\\text {tot}}$$ σ tot , parameters of the nuclear slope, and the $$\\rho $$ ρ -parameter defined as the ratio of the real part to the imaginary part of the elastic-scattering litude in the limit $$t \\rightarrow 0$$ t → 0 . These parameters are determined from a fit to the differential elastic cross section using the optical theorem and different parameterizations of the t -dependence. The results for $$\\sigma _{\\text {tot}}$$ σ tot and $$\\rho $$ ρ are $$\\begin{aligned} \\sigma _{\\text {tot}}(pp\\rightarrow X) = 104.7 \\pm 1.1 \\ \\text{ mb },\\quad \\rho = 0.098 \\pm 0.011 . \\end{aligned}$$ σ tot ( p p → X ) = 104.7 ± 1.1 mb , ρ = 0.098 ± 0.011 . The uncertainty in $$\\sigma _{\\text {tot}}$$ σ tot is dominated by the luminosity measurement, and in $$\\rho $$ ρ by imperfect knowledge of the detector alignment and by modelling of the nuclear litude.
Measurements of $$W^{+}W^{-}$$ production in decay topologies inspired by searches for electroweak supersymmetry
Publisher: Springer Science and Business Media LLC
Date: 10-08-2023
DOI: 10.1140/EPJC/S10052-023-11508-9
Abstract: This paper presents a measurement of fiducial and differential cross-sections for $$W^{+}W^{-}$$ W + W - production in proton–proton collisions at $$\\sqrt{s}=13$$ s = 13 TeV with the ATLAS experiment at the Large Hadron Collider using a dataset corresponding to an integrated luminosity of 139 fb $$^{-1}$$ - 1 . Events with exactly one electron, one muon and no hadronic jets are studied. The fiducial region in which the measurements are performed is inspired by searches for the electroweak production of supersymmetric charginos decaying to two-lepton final states. The selected events have moderate values of missing transverse momentum and the ‘stransverse mass’ variable $$m_{\\textrm{T2}}$$ m T2 , which is widely used in searches for supersymmetry at the LHC. The ranges of these variables are chosen so that the acceptance is enhanced for direct $$W^{+}W^{-}$$ W + W - production and suppressed for production via top quarks, which is treated as a background. The fiducial cross-section and particle-level differential cross-sections for six variables are measured and compared with two theoretical SM predictions from perturbative QCD calculations.
Measurement of the relative
B c ±
Publisher:
American Physical Society (APS)
Date:
26-07-2021
Publisher: American Physical Society (APS)
Date: 26-07-2021
Search for excited τ-leptons and leptoquarks in the final state with τ-leptons and jets in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 29-06-2023
Abstract: A search is reported for excited τ -leptons and leptoquarks in events with two hadronically decaying τ -leptons and two or more jets. The search uses proton-proton ( pp ) collision data at $$ \\sqrt{s} $$ s = 13 TeV recorded by the ATLAS experiment during the Run 2 of the Large Hadron Collider in 2015–2018. The total integrated luminosity is 139 fb − 1 . The excited τ -lepton is assumed to be produced and to decay via a four-fermion contact interaction into an ordinary τ -lepton and a quark-antiquark pair. The leptoquarks are assumed to be produced in pairs via the strong interaction, and each leptoquark is assumed to couple to a charm or lighter quark and a τ -lepton. No excess over the background prediction is observed. Excited τ -leptons with masses below 2.8 TeV are excluded at 95% CL in scenarios with the contact interaction scale Λ set to 10 TeV. At the extreme limit of model validity where Λ is set equal to the excited τ -lepton mass, excited τ -leptons with masses below 4.6 TeV are excluded. Leptoquarks with masses below 1.3 TeV are excluded at 95% CL if their branching ratio to a charm quark and a τ -lepton equals 1. The analysis does not exploit flavour-tagging in the signal region.
Measurement of the Lund Jet Plane Using Charged Particles in 13 TeV Proton-Proton Collisions with the ATLAS Detector
Publisher: American Physical Society (APS)
Date: 04-06-2020
Search for Higgs boson production in association with a high-energy photon via vector-boson fusion with decay into bottom quark pairs at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 03-2021
Abstract: A search is presented for the production of the Standard Model Higgs boson in association with a high-energy photon. With a focus on the vector-boson fusion process and the dominant Higgs boson decay into b -quark pairs, the search benefits from a large reduction of multijet background compared to more inclusive searches. Results are reported from the analysis of 132 fb − 1 of pp collision data at $$ \\sqrt{s} $$ s = 13 TeV collected with the ATLAS detector at the LHC. The measured Higgs boson signal yield in this final-state signature is 1 . 3 ± 1 . 0 times the Standard Model prediction. The observed significance of the Higgs boson signal above the background is 1 . 3 standard deviations, compared to an expected significance of 1 . 0 standard deviations.
Differential cross-section measurements for the electroweak production of dijets in association with a Z boson in proton–proton collisions at ATLAS
Publisher: Springer Science and Business Media LLC
Date: 02-2021
DOI: 10.1140/EPJC/S10052-020-08734-W
Abstract: Differential cross-section measurements are presented for the electroweak production of two jets in association with a Z boson. These measurements are sensitive to the vector-boson fusion production mechanism and provide a fundamental test of the gauge structure of the Standard Model. The analysis is performed using proton–proton collision data collected by ATLAS at $$\\sqrt{s}=13\\ \\hbox {TeV}$$ s = 13 TeV and with an integrated luminosity of $$139\\ \\hbox {fb}^{-1}$$ 139 fb - 1 . The differential cross-sections are measured in the $$Z\\rightarrow \\ell ^+\\ell ^-$$ Z → ℓ + ℓ - decay channel ( $$\\ell =e,\\mu $$ ℓ = e , μ ) as a function of four observables: the dijet invariant mass, the rapidity interval spanned by the two jets, the signed azimuthal angle between the two jets, and the transverse momentum of the dilepton pair. The data are corrected for the effects of detector inefficiency and resolution and are sufficiently precise to distinguish between different state-of-the-art theoretical predictions calculated using Powheg+Pythia8 , Herwig7+Vbfnlo and Sherpa 2.2. The differential cross-sections are used to search for anomalous weak-boson self-interactions using a dimension-six effective field theory. The measurement of the signed azimuthal angle between the two jets is found to be particularly sensitive to the interference between the Standard Model and dimension-six scattering litudes and provides a direct test of charge-conjugation and parity invariance in the weak-boson self-interactions.
Jet energy scale and resolution measured in proton–proton collisions at $$\sqrt{s}=13$$ TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 08-2021
DOI: 10.1140/EPJC/S10052-021-09402-3
Abstract: Jet energy scale and resolution measurements with their associated uncertainties are reported for jets using 36–81 fb $$^{-1}$$ - 1 of proton–proton collision data with a centre-of-mass energy of $$\sqrt{s}=13$$ s = 13 $${\text {Te}}{\text {V}}$$ TeV collected by the ATLAS detector at the LHC. Jets are reconstructed using two different input types: topo-clusters formed from energy deposits in calorimeter cells, as well as an algorithmic combination of charged-particle tracks with those topo-clusters, referred to as the ATLAS particle-flow reconstruction method. The anti- $$k_t$$ k t jet algorithm with radius parameter $$R=0.4$$ R = 0.4 is the primary jet definition used for both jet types. This result presents new jet energy scale and resolution measurements in the high pile-up conditions of late LHC Run 2 as well as a full calibration of particle-flow jets in ATLAS. Jets are initially calibrated using a sequence of simulation-based corrections. Next, several in situ techniques are employed to correct for differences between data and simulation and to measure the resolution of jets. The systematic uncertainties in the jet energy scale for central jets ( $$|\eta | .2$$ | η | 1.2 ) vary from 1% for a wide range of high- $$p_{{\text {T}}}$$ p T jets ( $$250 _{{\text {T}}} ~{\text {Ge}}{\text {V}}$$ 250 p T 2000 GeV ), to 5% at very low $$p_{{\text {T}}}$$ p T ( $$20~{\text {Ge}}{\text {V}}$$ 20 GeV ) and 3.5% at very high $$p_{{\text {T}}}$$ p T ( $$ .5~{\text {Te}}{\text {V}}$$ 2.5 TeV ). The relative jet energy resolution is measured and ranges from ( $$24 \pm 1.5$$ 24 ± 1.5 )% at 20 $${\text {Ge}}{\text {V}}$$ GeV to ( $$6 \pm 0.5$$ 6 ± 0.5 )% at 300 $${\text {Ge}}{\text {V}}$$ GeV .
Combination of the W boson polarization measurements in top quark decays using ATLAS and CMS data at $$ \sqrt{s} $$ = 8 TeV
Publisher: Springer Science and Business Media LLC
Date: 08-2020
Abstract: The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb − 1 for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal ( F 0 ), left-handed ( F L ), or right-handed ( F R ) polarizations. The resulting combined measurements of the polarization fractions are F 0 = 0 . 693 ± 0 . 014 and F L = 0 . 315 ± 0 . 011. The fraction F R is calculated from the unitarity constraint to be F R = − 0 . 008 ± 0 . 007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for F 0 ( F L ) with respect to the most precise single measurement. A limit on anomalous right-handed vector ( V R ), and left- and right-handed tensor ( g L , g R ) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [ − 0 . 11 , 0 . 16] for V R , [ − 0 . 08 , 0 . 05] for g L , and [ − 0 . 04 , 0 . 02] for g R , at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived.
AtlFast3: The Next Generation of Fast Simulation in ATLAS
Publisher: Springer Science and Business Media LLC
Date: 11-03-2022
DOI: 10.1007/S41781-021-00079-7
Abstract: The ATLAS experiment at the Large Hadron Collider has a broad physics programme ranging from precision measurements to direct searches for new particles and new interactions, requiring ever larger and ever more accurate datasets of simulated Monte Carlo events. Detector simulation with Geant4 is accurate but requires significant CPU resources. Over the past decade, ATLAS has developed and utilized tools that replace the most CPU-intensive component of the simulation—the calorimeter shower simulation—with faster simulation methods. Here, AtlFast3, the next generation of high-accuracy fast simulation in ATLAS, is introduced. AtlFast3 combines parameterized approaches with machine-learning techniques and is deployed to meet current and future computing challenges, and simulation needs of the ATLAS experiment. With highly accurate performance and significantly improved modelling of substructure within jets, AtlFast3 can simulate large numbers of events for a wide range of physics processes.
Search for flavor-changing neutral-current couplings between the top quark and the
Z
Publisher: American Physical Society (APS)
Date: 30-08-2023
Measurement of the jet mass in high transverse momentum Z (
Publisher:
Elsevier BV
Date:
2021
Publisher: Elsevier BV
Date: 2021
Search for charginos and neutralinos in final states with two boosted hadronically decaying bosons and missing transverse momentum in
Publisher:
American Physical Society (APS)
Date:
27-12-2021
Publisher: American Physical Society (APS)
Date: 27-12-2021
Search for the charged-lepton-flavor-violating decay
Z → e <
Publisher: American Physical Society (APS)
Date: 25-08-2023
Search for displaced photons produced in exotic decays of the Higgs boson using 13 TeV
p p
Publisher:
American Physical Society (APS)
Date:
21-08-2023
Publisher: American Physical Society (APS)
Date: 21-08-2023
A search for heavy Higgs bosons decaying into vector bosons in same-sign two-lepton final states in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 26-07-2023
Abstract: A search for heavy Higgs bosons produced in association with a vector boson and decaying into a pair of vector bosons is performed in final states with two leptons (electrons or muons) of the same electric charge, missing transverse momentum and jets. A data s le of proton–proton collisions at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018 is used. The data correspond to a total integrated luminosity of 139 fb − 1 . The observed data are in agreement with Standard Model background expectations. The results are interpreted using higher-dimensional operators in an effective field theory. Upper limits on the production cross-section are calculated at 95% confidence level as a function of the heavy Higgs boson’s mass and coupling strengths to vector bosons. Limits are set in the Higgs boson mass range from 300 to 1500 GeV, and depend on the assumed couplings. The highest excluded mass for a heavy Higgs boson with the coupling combinations explored is 900 GeV. Limits on coupling strengths are also provided.
Search for new phenomena in multi-body invariant masses in events with at least one isolated lepton and two jets using $$ \sqrt{s} $$ = 13 TeV proton–proton collision data collected by the ATLAS detec
Publisher: Springer Science and Business Media LLC
Date: 26-07-2023
Abstract: A search for resonances in events with at least one isolated lepton ( e or μ ) and two jets is performed using 139 fb − 1 of $$ \\sqrt{s} $$ s = 13 TeV proton–proton collision data recorded by the ATLAS detector at the LHC. Deviations from a smoothly falling background hypothesis are tested in three- and four-body invariant mass distributions constructed from leptons and jets, including jets identified as originating from bottom quarks. Model-independent limits on generic resonances characterised by cascade decays of particles leading to multiple jets and leptons in the final state are presented. The limits are calculated using Gaussian shapes with different widths for the invariant masses. The multi-body invariant masses are also used to set 95% confidence level upper limits on the cross-section times branching ratios for the production and subsequent decay of resonances predicted by several new physics scenarios.
Measurement of electroweak $$ Z\left(\nu \overline{\nu}\right)\gamma jj $$ production and limits on anomalous quartic gauge couplings in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detecto
Publisher: Springer Science and Business Media LLC
Date: 14-06-2023
Abstract: The electroweak production of $$ Z\\left(\\nu \\overline{\\nu}\\right)\\gamma $$ Z ν ν ¯ γ in association with two jets is studied in a regime with a photon of high transverse momentum above 150 GeV using proton–proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider. The analysis uses a data s le with an integrated luminosity of 139 fb − 1 collected by the ATLAS detector during the 2015–2018 LHC data-taking period. This process is an important probe of the electroweak symmetry breaking mechanism in the Standard Model and is sensitive to quartic gauge boson couplings via vector-boson scattering. The fiducial $$ Z\\left(\\nu \\overline{\\nu}\\right)\\gamma jj $$ Z ν ν ¯ γjj cross section for electroweak production is measured to be $$ {0.77}_{-0.30}^{+0.34} $$ 0.77 − 0.30 + 0.34 fb and is consistent with the Standard Model prediction. Evidence of electroweak $$ Z\\left(\\nu \\overline{\\nu}\\right)\\gamma jj $$ Z ν ν ¯ γjj production is found with an observed significance of 3.2 σ for the background-only hypothesis, compared with an expected significance of 3.7 σ . The combination of this result with the previously published ATLAS observation of electroweak $$ Z\\left(\\nu \\overline{\\nu}\\right)\\gamma jj $$ Z ν ν ¯ γjj production yields an observed (expected) signal significance of 6.3 σ (6.6 σ ). Limits on anomalous quartic gauge boson couplings are obtained in the framework of effective field theory with dimension-8 operators.
Evidence of off-shell Higgs boson production from ZZ leptonic decay channels and constraints on its total width with the ATLAS detector
Publisher: Elsevier BV
Date: 11-2023
Search for $$ t\overline{t}H/A\to t\overline{t}t\overline{t} $$ production in the multilepton final state in proton–proton collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 26-07-2023
Abstract: A search for a new heavy scalar or pseudo-scalar Higgs boson ( H/A ) produced in association with a pair of top quarks, with the Higgs boson decaying into a pair of top quarks ( H/A → $$ t\\overline{t} $$ t t ¯ ) is reported. The search targets a final state with exactly two leptons with same-sign electric charges or at least three leptons. The analysed dataset corresponds to an integrated luminosity of 139 fb − 1 of proton–proton collisions collected at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Two multivariate classifiers are used to separate the signal from the background. No significant excess of events over the Standard Model expectation is observed. The results are interpreted in the context of a type-II two-Higgs-doublet model. The observed (expected) upper limits at 95% confidence level on the $$ t\\overline{t}H/A $$ t t ¯ H / A production cross-section times the branching ratio of H/A → $$ t\\overline{t} $$ t t ¯ range between 14 (10) fb and 6 (5) fb for a heavy Higgs boson with mass between 400 GeV and 1000 GeV, respectively. Assuming that only one particle, either the scalar H or the pseudo-scalar A , contributes to the $$ t\\overline{t}t\\overline{t} $$ t t ¯ t t ¯ final state, values of tan β below 1.2 or 0.5 are excluded for a mass of 400 GeV or 1000 GeV, respectively. These exclusion ranges increase to tan β below 1.6 or 0.6 when both particles are considered.
Measurement of the production of a
W
Publisher:
American Physical Society (APS)
Date:
14-08-2023
Publisher: American Physical Society (APS)
Date: 14-08-2023
Measurement of the cross-sections of the electroweak and total production of a Zγ pair in association with two jets in pp collisions at
Publisher:
Elsevier BV
Date:
11-2023
Publisher: Elsevier BV
Date: 11-2023
Cross-section measurements for the production of a Z boson in association with high-transverse-momentum jets in pp collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 14-06-2023
Abstract: Cross-section measurements for a Z boson produced in association with high-transverse-momentum jets ( p T ≥ 100 GeV) and decaying into a charged-lepton pair ( e + e − , μ + μ − ) are presented. The measurements are performed using proton–proton collisions at $$ \\sqrt{s} $$ s = 13 TeV corresponding to an integrated luminosity of 139 fb − 1 collected by the ATLAS experiment at the LHC. Measurements of angular correlations between the Z boson and the closest jet are performed in events with at least one jet with p T ≥ 500 GeV. Event topologies of particular interest are the collinear emission of a Z boson in dijet events and a boosted Z boson recoiling against a jet. Fiducial cross sections are compared with state-of-the-art theoretical predictions. The data are found to agree with next-to-next-to-leading-order predictions by NNLO jet and with the next-to-leading-order multi-leg generators M ad G raph 5_ a MC@NLO and S herpa .
Search for pair-produced scalar and vector leptoquarks decaying into third-generation quarks and first- or second-generation leptons in pp collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 27-06-2023
Abstract: A search for pair-produced scalar and vector leptoquarks decaying into quarks and leptons of different generations is presented. It uses the full LHC Run 2 (2015–2018) data set of 139 fb − 1 collected with the ATLAS detector in proton–proton collisions at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV. Scalar leptoquarks with charge −(1 / 3) e as well as scalar and vector leptoquarks with charge +(2 / 3) e are considered. All possible decays of the pair-produced leptoquarks into quarks of the third generation ( t, b ) and charged or neutral leptons of the first or second generation ( e, μ, ν ) with exactly one electron or muon in the final state are investigated. No significant deviations from the Standard Model expectation are observed. Upper limits on the production cross-section are provided for eight models as a function of the leptoquark mass and the branching ratio of the leptoquark into the charged or neutral lepton. In addition, lower limits on the leptoquark masses are derived for all models across a range of branching ratios. Two of these models have the goal of providing an explanation for the recent B -anomalies. In both models, a vector leptoquark decays into charged and neutral leptons of the second generation with a similar branching fraction. Lower limits of 1980 GeV and 1710 GeV are set on the leptoquark mass for these two models.
Observation of the associated production of a top quark and a Z boson in pp collisions at $$ \sqrt{s} $$= 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 07-2020
Abstract: Single top-quark production in association with a Z boson, where the Z boson decays to a pair of charged leptons, is measured in the trilepton channel. The proton-proton collision data collected by the ATLAS experiment from 2015 to 2018 at a centre-of-mass energy of 13 TeV are used, corresponding to an integrated luminosity of 139 fb − 1 . Events containing three isolated charged leptons (electrons or muons) and two or three jets, one of which is identified as containing a b -hadron, are selected. The main backgrounds are from $$ t\\overline{t}Z $$ t t ¯ Z and diboson production. Neural networks are used to improve the background rejection and extract the signal. The measured cross-section for t ℓ + ℓ − q production, including non-resonant dilepton pairs with $$ {m}_{{\\mathrm{\\ell}}^{+}{\\mathrm{\\ell}}^{-}} $$ m ℓ + ℓ − 30 GeV, is 97 ± 13 (stat.) ± 7 (syst.) fb, consistent with the Standard Model prediction.
Exclusive dielectron production in ultraperipheral Pb+Pb collisions at $$ \sqrt{s_{\textrm{NN}}} $$ = 5.02 TeV with ATLAS
Publisher: Springer Science and Business Media LLC
Date: 27-06-2023
Abstract: Exclusive production of dielectron pairs, γγ → e + e − , is studied using $$ {\mathcal{L}}_{\textrm{int}} $$ L int = 1 . 72 nb − 1 of data from ultraperipheral collisions of lead nuclei at $$ \sqrt{s_{\textrm{NN}}} $$ s NN = 5 . 02 TeV recorded by the ATLAS detector at the LHC. The process of interest proceeds via photon–photon interactions in the strong electromagnetic fields of relativistic lead nuclei. Dielectron production is measured in the fiducial region defined by following requirements: electron transverse momentum $$ {p}_{\textrm{T}}^e $$ p T e 2 . 5 GeV, absolute electron pseudorapidity |η e | 2 . 5, dielectron invariant mass m ee 5 GeV, and dielectron transverse momentum $$ {p}_{\textrm{T}}^{ee} $$ p T ee 2 GeV. Differential cross-sections are measured as a function of m ee , average $$ {p}_{\textrm{T}}^e $$ p T e , absolute dielectron rapidity | y ee |, and scattering angle in the dielectron rest frame, |cos θ * |, in the inclusive s le, and also with a requirement of no activity in the forward direction. The total integrated fiducial cross-section is measured to be $$ 215\pm 1{\left(\textrm{stat}.\right)}_{-20}^{+23}\left(\textrm{syst}.\right)\pm 4\left(\textrm{lumi}.\right) $$ 215 ± 1 stat . − 20 + 23 syst . ± 4 lumi . μ b. Within experimental uncertainties the measured integrated cross-section is in good agreement with the QED predictions from the Monte Carlo programs S tarlight and S uper C hic , confirming the broad features of the initial photon fluxes. The differential cross-sections show systematic differences from these predictions which are more pronounced at high |y ee | and | cos θ * | values.
A search for the Zγ decay mode of the Higgs boson in pp collisions at s Publisher:
Elsevier BV
Date:
10-2020
Publisher: Elsevier BV
Date: 10-2020
Test of the universality of τ and μ lepton couplings in W-boson decays with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 07-2021
DOI: 10.1038/S41567-021-01236-W
Abstract: The standard model of particle physics encapsulates our best current understanding of physics at the smallest scales. A fundamental axiom of this theory is the universality of the couplings of the different generations of leptons to the electroweak gauge bosons. The measurement of the ratio of the decay rate of W bosons to τ leptons and muons, R ( τ / μ ), constitutes an important test of this axiom. Using 139 fb −1 of proton–proton collisions recorded with the ATLAS detector at a centre-of-mass energy of 13 TeV, we report a measurement of this quantity from di-leptonic $$t\\overline{t}$$ t t ¯ events where the top quarks decay into a W boson and a bottom quark. We can distinguish muons originating from W bosons and those originating from an intermediate τ lepton through the muon transverse impact parameter and differences in the muon transverse momentum spectra. The measured value of R ( τ / μ ) is 0.992 ± 0.013 [± 0.007(stat) ± 0.011(syst)] and is in agreement with the hypothesis of universal lepton couplings as postulated in the standard model. This is the only such measurement from the Large Hadron Collider, so far, and obtains twice the precision of previous measurements.
A search for the decays of stopped long-lived particles at $$ \sqrt{\mathrm{s}} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Abstract: A search for long-lived particles, which have come to rest within the ATLAS detector, is presented. The subsequent decays of these particles can produce high-momentum jets, resulting in large out-of-time energy deposits in the ATLAS calorimeters. These de- cays are detected using data collected during periods in the LHC bunch structure when collisions are absent. The analysed dataset is composed of events from proton-proton collisions produced by the Large Hadron Collider at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV and recorded by the ATLAS experiment during 2017 and 2018. The dataset used for this search corresponds to a total live time of 579 hours. The results of this search are used to derive lower limits on the mass of gluino R -hadrons, assuming a branching fraction $$ \\mathcal{B}\\left(\\overset{\\sim }{g}\\to q\\overline{q}{\\chi}_1^0\\right) $$ B g ~ → q q ¯ χ 1 0 = 100%, with masses of up to 1 . 4 TeV excluded for gluino lifetimes of 10 − 5 to 10 3 s.
Search for Lepton-Flavor Violation in
Z
Publisher:
American Physical Society (APS)
Date:
28-12-2021
Publisher: American Physical Society (APS)
Date: 28-12-2021
Search for supersymmetry in events with four or more charged leptons in 139 fb−1 of $$ \sqrt{s} $$ = 13 TeV pp collisions with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 07-2021
Abstract: A search for supersymmetry in events with four or more charged leptons (electrons, muons and τ -leptons) is presented. The analysis uses a data s le corresponding to 139 fb − 1 of proton-proton collisions delivered by the Large Hadron Collider at $$ \\sqrt{s} $$ s = 13 TeV and recorded by the ATLAS detector. Four-lepton signal regions with up to two hadronically decaying τ -leptons are designed to target several supersymmetric models, while a general five-lepton signal region targets any new physics phenomena leading to a final state with five charged leptons. Data yields are consistent with Standard Model expectations and results are used to set upper limits on contributions from processes beyond the Standard Model. Exclusion limits are set at the 95% confidence level in simplified models of general gauge-mediated supersymmetry, excluding higgsino masses up to 540 GeV. In R -parity-violating simplified models with decays of the lightest supersymmetric particle to charged leptons, lower limits of 1 . 6 TeV, 1 . 2 TeV, and 2 . 5 TeV are placed on wino, slepton and gluino masses, respectively.
Observation of four-top-quark production in the multilepton final state with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 12-06-2023
DOI: 10.1140/EPJC/S10052-023-11573-0
Abstract: This paper presents the observation of four-top-quark ( $$t\\bar{t}t\\bar{t}$$ t t ¯ t t ¯ ) production in proton-proton collisions at the LHC. The analysis is performed using an integrated luminosity of 140 $$\\hbox {fb}^{-1}$$ fb - 1 at a centre-of-mass energy of 13 TeV collected using the ATLAS detector. Events containing two leptons with the same electric charge or at least three leptons (electrons or muons) are selected. Event kinematics are used to separate signal from background through a multivariate discriminant, and dedicated control regions are used to constrain the dominant backgrounds. The observed (expected) significance of the measured $$t\\bar{t}t\\bar{t}$$ t t ¯ t t ¯ signal with respect to the standard model (SM) background-only hypothesis is 6.1 (4.3) standard deviations. The $$t\\bar{t}t\\bar{t}$$ t t ¯ t t ¯ production cross section is measured to be $$22.5^{+6.6}_{-5.5}$$ 22 . 5 - 5.5 + 6.6 fb, consistent with the SM prediction of $$12.0 \\pm 2.4$$ 12.0 ± 2.4 fb within 1.8 standard deviations. Data are also used to set limits on the three-top-quark production cross section, being an irreducible background not measured previously, and to constrain the top-Higgs Yukawa coupling and effective field theory operator coefficients that affect $$t\\bar{t}t\\bar{t}$$ t t ¯ t t ¯ production.
Measurement of the total and differential Higgs boson production cross-sections at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector by combining the H → ZZ* → 4ℓ and H → γγ decay channels
Publisher: Springer Science and Business Media LLC
Date: 04-05-2023
Abstract: The total and differential Higgs boson production cross-sections are measured through a combined statistical analysis of the H → ZZ * → 4 ℓ and H → γγ decay channels. The results are based on a dataset of 139 fb − 1 of proton–proton collisions at a centre-of-mass energy of 13 TeV, recorded by the ATLAS detector at the Large Hadron Collider. The measured total Higgs boson production cross-section is $$ {55.5}_{-3.8}^{+4.0} $$ 55.5 − 3.8 + 4.0 pb, consistent with the Standard Model prediction of 55 . 6 ± 2 . 5 pb. All results from the two decay channels are compatible with each other, and their combination agrees with the Standard Model predictions. A combined statistical interpretation of the measured fiducial cross-sections as a function of the Higgs boson transverse momentum is performed in order to probe the Yukawa couplings to the bottom and charm quarks. A similar interpretation is performed by including also the constraints from the measurements of Higgs boson production in association with a W or Z boson in the H → $$ b\\overline{b} $$ b b ¯ and $$ c\\overline{c} $$ c c ¯ decay channels.
Search for resonant WZ production in the fully leptonic final state in proton–proton collisions at $$\mathbf {\sqrt{s} = 13}$$ TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 18-07-2023
DOI: 10.1140/EPJC/S10052-023-11437-7
Abstract: A search for a WZ resonance, in the fully leptonic final state (electrons or muons), is performed using 139 fb $$^{-1}$$ - 1 of data collected at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. The results are interpreted in terms of a singly charged Higgs boson of the Georgi–Machacek model, produced by WZ fusion, and of a Heavy Vector Triplet, with the resonance produced by WZ fusion or the Drell–Yan process. No significant excess over the Standard Model prediction is observed and limits are set on the production cross-section times branching ratio as a function of the resonance mass for these processes.
Search for associated production of a Z boson with an invisibly decaying Higgs boson or dark matter candidates at <
Publisher: Elsevier BV
Date: 06-2022
Measurement of Suppression of Large-Radius Jets and Its Dependence on Substructure in
Pb +<
Publisher: American Physical Society (APS)
Date: 23-10-2023
Measurement of single top-quark production in the s-channel in proton–proton collisions at $$ \sqrt{s} $$ = 13 TeV with the ATLAS detector
Publisher: Springer Science and Business Media LLC
Date: 27-06-2023
Abstract: A measurement of single top-quark production in the s-channel is performed in proton–proton collisions at a centre-of-mass energy of 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. The dataset corresponds to an integrated luminosity of 139 fb − 1 . The analysis is performed on events with an electron or muon, missing transverse momentum and exactly two b -tagged jets in the final state. A discriminant based on matrix element calculations is used to separate single-top-quark s-channel events from the main background contributions, which are top-quark pair production and W -boson production in association with jets. The observed (expected) signal significance over the background-only hypothesis is 3.3 (3.9) standard deviations, and the measured cross-section is $$ \\sigma ={8.2}_{-2.9}^{+3.5} $$ σ = 8.2 − 2.9 + 3.5 pb, consistent with the Standard Model prediction of $$ {\\sigma}^{\\textrm{SM}}={10.32}_{-0.36}^{+0.40} $$ σ SM = 10.32 − 0.36 + 0.40 pb.
Search for new phenomena in
p p
Publisher:
American Physical Society (APS)
Date:
21-12-2021
Publisher: American Physical Society (APS)
Date: 21-12-2021
Performance of the upgraded PreProcessor of the ATLAS Level-1 Calorimeter Trigger
Publisher: IOP Publishing
Date: 10-11-2020
Integrated and differential fiducial cross-section measurements for the vector boson fusion production of the Higgs boson in the
Publisher:
American Physical Society (APS)
Date:
11-10-2023
Publisher: American Physical Society (APS)
Date: 11-10-2023
Related Organisations
P.N. Lebedev Physical Institute Of The Russian Academy Of Sciences
Location: No location found
P.N. Lebedev Physical Institute Of The Russian Academy Of Sciences
Location: Russian Federation
Related Funding Activities
No related grants have been discovered for Oleg Meshkov.