ORCID Profile
0000-0003-4368-9285
Current Organisation
Royal Holloway University of London
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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.
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.
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.
Publisher: Springer Science and Business Media LLC
Date: 31-10-2023
Publisher: Elsevier BV
Date: 08-2023
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 + .
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.
Publisher: Elsevier BV
Date: 08-2023
Publisher: American Physical Society (APS)
Date: 30-10-2023
Publisher: American Physical Society (APS)
Date: 05-09-2023
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.
Publisher: American Physical Society (APS)
Date: 16-08-2023
Publisher: American Physical Society (APS)
Date: 21-08-2023
Publisher: Elsevier BV
Date: 08-2023
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.
Publisher: American Physical Society (APS)
Date: 18-09-2023
Publisher: Elsevier BV
Date: 11-2023
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.
Publisher: Elsevier BV
Date: 11-2023
Publisher: American Physical Society (APS)
Date: 14-08-2023
Publisher: Springer Science and Business Media LLC
Date: 05-09-2023
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.
Publisher: Elsevier BV
Date: 10-2023
Publisher: American Physical Society (APS)
Date: 16-10-2023
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.
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).
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 .
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.
Publisher: American Physical Society (APS)
Date: 09-08-2023
Publisher: Springer Science and Business Media LLC
Date: 23-01-2118
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.
Publisher: Elsevier BV
Date: 08-2023
Publisher: Springer Science and Business Media LLC
Date: 09-2023
Publisher: Elsevier BV
Date: 07-2023
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.
Publisher: American Physical Society (APS)
Date: 31-01-2018
Publisher: American Physical Society (APS)
Date: 23-10-2023
Publisher: Elsevier BV
Date: 08-2023
Publisher: American Physical Society (APS)
Date: 13-10-2023
Publisher: Elsevier BV
Date: 11-2023
Publisher: American Physical Society (APS)
Date: 19-07-2023
Publisher: American Physical Society (APS)
Date: 11-10-2023
Publisher: Elsevier BV
Date: 11-2023
Location: United Kingdom of Great Britain and Northern Ireland
Location: Brazil
No related grants have been discovered for Sudha Ahuja.