ORCID Profile
0000-0002-3826-3442
Current Organisations
University of Coimbra
,
Laboratório de Instrumentacao e Física Experimental de Partículas
,
Universidade de Lisboa Faculdade de Ciências
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Publisher: Springer Science and Business Media LLC
Date: 12-2020
DOI: 10.1140/EPJC/S10052-020-08477-8
Abstract: The jet energy scale, jet energy resolution, and their systematic uncertainties are measured for jets reconstructed with the ATLAS detector in 2012 using proton–proton data produced at a centre-of-mass energy of 8 TeV with an integrated luminosity of $$20 \\, \\hbox {fb}^{-1}$$ 20 fb - 1 . Jets are reconstructed from clusters of energy depositions in the ATLAS calorimeters using the anti- $$k_t$$ k t algorithm. A jet calibration scheme is applied in multiple steps, each addressing specific effects including mitigation of contributions from additional proton–proton collisions, loss of energy in dead material, calorimeter non-compensation, angular biases and other global jet effects. The final calibration step uses several in situ techniques and corrects for residual effects not captured by the initial calibration. These analyses measure both the jet energy scale and resolution by exploiting the transverse momentum balance in $$\\gamma $$ γ + jet, Z + jet, dijet, and multijet events. A statistical combination of these measurements is performed. In the central detector region, the derived calibration has a precision better than 1% for jets with transverse momentum $$150 \\, \\hbox {GeV} p_{{\\mathrm {T}}} $$ 150 GeV p T 1500 GeV, and the relative energy resolution is $$(8.4\\pm 0.6)\\%$$ ( 8.4 ± 0.6 ) % for $$p_{{\\mathrm {T}}}= 100 \\, \\hbox {GeV}$$ p T = 100 GeV and $$(23\\pm 2)\\%$$ ( 23 ± 2 ) % for $$p_{{\\mathrm {T}}}= 20 \\, \\hbox {GeV}$$ p T = 20 GeV . The calibration scheme for jets with radius parameter $$R=1.0$$ R = 1.0 , for which jets receive a dedicated calibration of the jet mass, is also discussed.
Publisher: IOP Publishing
Date: 04-04-2013
Publisher: Elsevier BV
Date: 2019
Publisher: Springer Science and Business Media LLC
Date: 05-2017
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 .
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.
Publisher: Springer Science and Business Media LLC
Date: 02-2018
Publisher: Springer Science and Business Media LLC
Date: 03-2018
Publisher: Elsevier BV
Date: 08-2018
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.
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.
Publisher: Elsevier BV
Date: 2014
Publisher: American Physical Society (APS)
Date: 21-09-2020
Publisher: IOP Publishing
Date: 19-05-2011
Publisher: Springer Science and Business Media LLC
Date: 06-2020
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.
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.
Publisher: American Physical Society (APS)
Date: 25-11-2020
Publisher: American Physical Society (APS)
Date: 05-08-2020
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.
Publisher: IOP Publishing
Date: 14-09-2020
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.
Publisher: American Physical Society (APS)
Date: 27-07-2020
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.
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.
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.
Publisher: American Physical Society (APS)
Date: 13-08-2020
Publisher: Elsevier BV
Date: 03-2012
Publisher: Springer Science and Business Media LLC
Date: 14-08-2017
DOI: 10.1038/NPHYS4208
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.
Publisher: Springer Science and Business Media LLC
Date: 11-2020
Publisher: American Physical Society (APS)
Date: 07-12-2020
Publisher: American Physical Society (APS)
Date: 17-12-2020
Publisher: American Physical Society (APS)
Date: 04-06-2020
Publisher: Elsevier BV
Date: 03-2011
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.
Publisher: American Physical Society (APS)
Date: 14-08-2020
Publisher: Springer Science and Business Media LLC
Date: 11-2017
Publisher: Elsevier BV
Date: 11-2017
Publisher: Elsevier BV
Date: 06-2018
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.
Publisher: American Physical Society (APS)
Date: 18-12-2020
Publisher: Elsevier BV
Date: 04-2018
Publisher: Elsevier BV
Date: 05-2015
Publisher: Elsevier BV
Date: 09-2018
Publisher: Elsevier BV
Date: 08-2020
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.
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.
Publisher: Elsevier BV
Date: 11-2020
Publisher: Elsevier BV
Date: 09-2012
Publisher: Springer Science and Business Media LLC
Date: 06-2018
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.
Publisher: Elsevier BV
Date: 10-2013
Publisher: American Physical Society (APS)
Date: 23-12-2020
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 ¯ .
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.
Publisher: Elsevier BV
Date: 10-2016
Publisher: Springer Science and Business Media LLC
Date: 02-2017
Publisher: Springer Science and Business Media LLC
Date: 03-2018
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.
Publisher: Elsevier BV
Date: 10-2020
Publisher: Springer Science and Business Media LLC
Date: 10-2020
Abstract: Figure 5b of the paper [1] contained a misinterpretation in the comparison between the reported new ATLAS measurement of the process pp → Xp and previously published CMS data [2]. The ATLAS measurement corresponds to cases where either proton dissociates.
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.
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.
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.
Publisher: Springer Science and Business Media LLC
Date: 11-2017
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.
Publisher: IOP Publishing
Date: 10-11-2020
Location: United Kingdom of Great Britain and Northern Ireland
Location: Portugal
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for José Gonçalo.