Yazar "Abicht, N.J." seçeneğine göre listele

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    Evidence for the Higgs boson decay to a Z boson and a photon at the LHC
    (American Physical Society, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    The first evidence for the Higgs boson decay to a Formula Presented boson and a photon is presented, with a statistical significance of 3.4 standard deviations. The result is derived from a combined analysis of the searches performed by the ATLAS and CMS Collaborations with proton-proton collision datasets collected at the CERN Large Hadron Collider (LHC) from 2015 to 2018. These correspond to integrated luminosities of around Formula Presented for each experiment, at a center-of-mass energy of 13 TeV. The measured signal yield is Formula Presented times the standard model prediction, and agrees with the theoretical expectation within 1.9 standard deviations. © 2024 CERN, for the ATLAS and CMSs Collaboration.
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    Measurement of the cross-sections of the electroweak and total production of a Z? pair in association with two jets in pp collisions at s=13 TeV with the ATLAS detector
    (Elsevier B.V., 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    This Letter presents the measurement of the fiducial and differential cross-sections of the electroweak production of a Z? pair in association with two jets. The analysis uses 140 fb?1 of LHC proton–proton collision data taken at s=13 TeV recorded by the ATLAS detector during the years 2015–2018. Events with a Z boson candidate decaying into either an e+e? or ?+?? pair, a photon and two jets are selected. The electroweak component is extracted by requiring a large dijet invariant mass and by using the information about the centrality of the system and is measured with an observed and expected significance well above five standard deviations. The fiducial pp?Z?jj cross-section for the electroweak production is measured to be 3.6 ± 0.5 fb. The total fiducial cross-section that also includes contributions where the jets arise from strong interactions is measured to be 16.8?1.8 +2.0 fb. The results are consistent with the Standard Model predictions. Differential cross-sections are also measured using the same events and are compared with parton-shower Monte Carlo simulations. Good agreement is observed between data and predictions. © 2023 The Author(s)
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    Measurement of the Higgs boson mass with H????? decays in 140 fb?1 of s=13 TeV pp collisions with the ATLAS detector
    (Elsevier B.V., 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    The mass of the Higgs boson is measured in the H??? decay channel, exploiting the high resolution of the invariant mass of photon pairs reconstructed from the decays of Higgs bosons produced in proton–proton collisions at a centre-of-mass energy s=13 TeV. The dataset was collected between 2015 and 2018 by the ATLAS detector at the Large Hadron Collider, and corresponds to an integrated luminosity of 140 fb?1. The measured value of the Higgs boson mass is 125.17±0.11(stat.)±0.09(syst.) GeV and is based on an improved energy scale calibration for photons, whose impact on the measurement is about four times smaller than in the previous publication. A combination with the corresponding measurement using 7 and 8 TeV pp collision ATLAS data results in a Higgs boson mass measurement of 125.22±0.11(stat.)±0.09(syst.) GeV. With an uncertainty of 1.1 per mille, this is currently the most precise measurement of the mass of the Higgs boson from a single decay channel. © 2023 The Author(s)
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    Measurement of the production cross-section of J/? and ?(2S) mesons in pp collisions at s=13 TeV with the ATLAS detector
    (Springer Nature, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    Measurements of the differential production cross-sections of prompt and non-prompt J/? and ?(2S) mesons with transverse momenta between 8 and 360 GeV and rapidity in the range |y|<2 are reported. Furthermore, measurements of the non-prompt fractions of J/? and ?(2S), and the prompt and non-prompt ?(2S)-to-J/? production ratios, are presented. The analysis is performed using 140 fb-1 of s=13 TeV pp collision data recorded by the ATLAS detector at the LHC during the years 2015–2018. © The Author(s) 2024.
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    Observation of four-top-quark production in the multilepton final state with the ATLAS detector
    (Springer Nature, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    This paper presents the observation of four-top-quark (tt¯ tt¯) production in proton-proton collisions at the LHC. The analysis is performed using an integrated luminosity of 140 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 tt¯ tt¯ signal with respect to the standard model (SM) background-only hypothesis is 6.1 (4.3) standard deviations. The tt¯ tt¯ production cross section is measured to be 22.5-5.5+6.6 fb, consistent with the SM prediction of 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 tt¯ tt¯ production. © 2023, The Author(s).
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    Observation of W?? triboson production in proton-proton collisions at s=13 TeV with the ATLAS detector
    (Elsevier B.V., 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    This letter reports the observation of W(??)?? production in proton-proton collisions. This measurement uses the full Run 2 sample of events recorded at a center-of-mass energy of s=13 TeV by the ATLAS detector at the LHC, corresponding to an integrated luminosity of 140 fb?1. Events with a leptonically-decaying W boson and at least two photons are considered. The background-only hypothesis is rejected with an observed and expected significance of 5.6 standard deviations. The inclusive fiducial production cross section of W(e?)?? and W(??)?? events is measured to be ?fid=13.8±1.1(stat)+2.1?2.0(syst)±0.1(lumi) fb, in agreement with the Standard Model prediction. © 2023 The Author(s)
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    A precise measurement of the Z-boson double-differential transverse momentum and rapidity distributions in the full phase space of the decay leptons with the ATLAS experiment at s=8 TeV
    (Springer Nature, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    This paper presents for the first time a precise measurement of the production properties of the Z boson in the full phase space of the decay leptons. This is in contrast to the many previous precise unfolded measurements performed in the fiducial phase space of the decay leptons. The measurement is obtained from proton–proton collision data collected by the ATLAS experiment in 2012 at s=8 TeV at the LHC and corresponding to an integrated luminosity of 20.2 fb-1. The results, based on a total of 15.3 million Z-boson decays to electron and muon pairs, extend and improve a previous measurement of the full set of angular coefficients describing Z-boson decay. The double-differential cross-section distributions in Z-boson transverse momentum pT and rapidity y are measured in the pole region, defined as 80<m??<100 GeV, over the range |y|<3.6. The total uncertainty of the normalised cross-section measurements in the peak region of the pT distribution is dominated by statistical uncertainties over the full range and increases as a function of rapidity from 0.5–1.0% for |y|<2.0 to 2-7% at higher rapidities. The results for the rapidity-dependent transverse momentum distributions are compared to state-of-the-art QCD predictions, which combine in the best cases approximate N4LL resummation with N3LO fixed-order perturbative calculations. The differential rapidity distributions integrated over pT are even more precise, with accuracies from 0.2–0.3% for |y|<2.0 to 0.4–0.9% at higher rapidities, and are compared to fixed-order QCD predictions using the most recent parton distribution functions. The agreement between data and predictions is quite good in most cases. © CERN for the benefit of The ATLAS Collaboration 2024.
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    Search for lepton-flavour violation in high-mass dilepton final states using 139 fb?1 of pp collisions at ?s = 13 TeV with the ATLAS detector
    (Springer Science and Business Media Deutschland GmbH, 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    A search is performed for a heavy particle decaying into different-flavour, dilepton final states, using 139 fb?1 of proton-proton collision data at s = 13 TeV collected in 2015–2018 by the ATLAS detector at the Large Hadron Collider. Final states with electrons, muons and hadronically decaying tau leptons are considered (e?, e? or ??). No significant excess over the Standard Model predictions is observed. Upper limits on the production cross-section are set as a function of the mass of a Z? boson, a supersymmetric ?-sneutrino, and a quantum black-hole. The observed 95% CL lower mass limits obtained on a typical benchmark model Z? boson are 5.0 TeV (e?), 4.0 TeV (e?), and 3.9 TeV (??), respectively. [Figure not available: see fulltext.]. © 2023, The Author(s).
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    Search for non-resonant Higgs boson pair production in the 2b+2?+ETmiss final state in pp collisions at s = 13 TeV with the ATLAS detector
    (Springer Science and Business Media Deutschland GmbH, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    A search for non-resonant Higgs boson pair (HH) production is presented, in which one of the Higgs bosons decays to a b-quark pair (bb¯) and the other decays to WW*, ZZ*, or ?+??, with in each case a final state with ?+??+ neutrinos (? = e, ?). The analysis targets separately the gluon-gluon fusion and vector boson fusion production modes. Data recorded by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV at the Large Hadron Collider, corresponding to an integrated luminosity of 140 fb?1, are used in this analysis. Events are selected to have exactly two b-tagged jets and two leptons with opposite electric charge and missing transverse momentum in the final state. These events are classified using multivariate analysis algorithms to separate the HH events from other Standard Model processes. No evidence of the signal is found. The observed (expected) upper limit on the cross-section for non-resonant Higgs boson pair production is determined to be 9.7 (16.2) times the Standard Model prediction at 95% confidence level. The Higgs boson self-interaction coupling parameter ?? and the quadrilinear coupling parameter ?2V are each separately constrained by this analysis to be within the ranges [?6.2, 13.3] and [?0.17, 2.4], respectively, at 95% confidence level, when all other parameters are fixed. © The Author(s) 2024.
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    Search for pair production of squarks or gluinos decaying via sleptons or weak bosons in final states with two same-sign or three leptons with the ATLAS detector
    (Springer Science and Business Media Deutschland GmbH, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    A search for pair production of squarks or gluinos decaying via sleptons or weak bosons is reported. The search targets a final state with exactly two leptons with same-sign electric charge or at least three leptons without any charge requirement. The analysed data set 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. Multiple signal regions are defined, targeting several SUSY simplified models yielding the desired final states. A single control region is used to constrain the normalisation of the WZ + jets background. No significant excess of events over the Standard Model expectation is observed. The results are interpreted in the context of several supersymmetric models featuring R-parity conservation or R-parity violation, yielding exclusion limits surpassing those from previous searches. In models considering gluino (squark) pair production, gluino (squark) masses up to 2.2 (1.7) TeV are excluded at 95% confidence level. © The Author(s) 2024.
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    Search for pair-production of vector-like quarks in pp collision events at s=13 TeV with at least one leptonically decaying Z boson and a third-generation quark with the ATLAS detector
    (Elsevier B.V., 2023) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    A search for the pair-production of vector-like quarks optimized for decays into a Z boson and a third-generation Standard Model quark is presented, using the full Run 2 dataset corresponding to 139fb?1 of pp collisions at s=13TeV, collected in 2015–2018 with the ATLAS detector at the Large Hadron Collider. The targeted final state is characterized by the presence of a Z boson with high transverse momentum, reconstructed from a pair of same-flavour leptons with opposite-sign charges, as well as by the presence of b-tagged jets and high-transverse-momentum large-radius jets reconstructed from calibrated smaller-radius jets. Events with exactly two or at least three leptons are used, which are further categorized by the presence of boosted W, Z, and Higgs bosons and top quarks. The categorization is performed using a neural-network-based boosted object tagger to enhance the sensitivity to signal relative to the background. No significant excess above the background expectation is observed and exclusion limits at 95% confidence level are set on the masses of the vector-like partners T and B of the top and bottom quarks, respectively. The limits depend on the branching ratio configurations and, in the case of 100% branching ratio for T?Zt and 100% branching ratio for B?Zb, this search sets the most stringent limits to date, allowing mT>1.60TeV and mB>1.42TeV, respectively. © 2023 The Author(s)
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    Search for the decay of the Higgs boson to a Z boson and a light pseudoscalar particle decaying to two photons
    (Elsevier B.V., 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    A search for the decay of the Higgs boson to a Z boson and a light, pseudoscalar particle, a, decaying respectively to two leptons and to two photons is reported. The search uses the full LHC Run 2 proton–proton collision data at s=13 TeV, corresponding to 139 fb?1 collected by the ATLAS detector. This is one of the first searches for this specific decay mode of the Higgs boson, and it probes unexplored parameter space in models with axion-like particles (ALPs) and extended scalar sectors. The mass of the a particle is assumed to be in the range 0.1–33 GeV. The data are analysed in two categories: a merged category where the photons from the a decay are reconstructed in the ATLAS calorimeter as a single cluster, and a resolved category in which two separate photons are detected. The main background processes are from Standard Model Z boson production in association with photons or jets. The data are in agreement with the background predictions, and upper limits on the branching ratio of the Higgs boson decay to Za times the branching ratio a??? are derived at the 95% confidence level and they range from 0.08% to 2% depending on the mass of the a particle. The results are also interpreted in the context of ALP models. © 2024 The Author(s)
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    Software Performance of the ATLAS Track Reconstruction for LHC Run 3
    (Springer Nature, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Çetin, Serkant Ali
    Charged particle reconstruction in the presence of many simultaneous proton–proton (pp) collisions in the LHC is a challenging task for the ATLAS experiment’s reconstruction software due to the combinatorial complexity. This paper describes the major changes made to adapt the software to reconstruct high-activity collisions with an average of 50 or more simultaneous pp interactions per bunch crossing (pile-up) promptly using the available computing resources. The performance of the key components of the track reconstruction chain and its dependence on pile-up are evaluated, and the improvement achieved compared to the previous software version is quantified. For events with an average of 60pp collisions per bunch crossing, the updated track reconstruction is twice as fast as the previous version, without significant reduction in reconstruction efficiency and while reducing the rate of combinatorial fake tracks by more than a factor two. © The Author(s) 2024.