Examinando por Autor "AbouZeid O.S."
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Ítem Alignment of the ATLAS Inner Detector in Run 2(Springer Science and Business Media Deutschland GmbH, 2020-12) Aad G.; Abbott B.; Abbott D.C.; Abud A.A.; Abeling K.; Abhayasinghe D.K.; Abidi S.H.; AbouZeid O.S.; Abraham N.L.; Abramowicz H.; Abreu H.; Abulaiti Y.The performance of the ATLAS Inner Detector alignment has been studied using pp collision data at s=13TeV collected by the ATLAS experiment during Run 2 (2015–2018) of the Large Hadron Collider (LHC). The goal of the detector alignment is to determine the detector geometry as accurately as possible and correct for time-dependent movements. The Inner Detector alignment is based on the minimization of track-hit residuals in a sequence of hierarchical levels, from global mechanical assembly structures to local sensors. Subsequent levels have increasing numbers of degrees of freedom; in total there are almost 750,000. The alignment determines detector geometry on both short and long timescales, where short timescales describe movements within an LHC fill. The performance and possible track parameter biases originating from systematic detector deformations are evaluated. Momentum biases are studied using resonances decaying to muons or to electrons. The residual sagitta bias and momentum scale bias after alignment are reduced to less than ∼0.1TeV-1 and 0.9 × 10 - 3, respectively. Impact parameter biases are also evaluated using tracks within jets. © 2020, The Author(s).Ítem Determination of jet calibration and energy resolution in proton–proton collisions at √s=8TeV using the ATLAS detector(Springer Science and Business Media Deutschland GmbH, 2020-12) Aaboud M.; Aad G.; Abbott B.; Abdinov O.; Abeloos B.; Abidi S.H; AbouZeid O.S.; Abraham N.L.; Abramowicz H.; Abreu H.; Abulaiti Y.; Acharya B.SThe 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 20fb-1. Jets are reconstructed from clusters of energy depositions in the ATLAS calorimeters using the anti-kt 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 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 150GeVenergy resolution is (8.4 ± 0.6) % for pT=100GeV and (23 ± 2) % for pT=20GeV. The calibration scheme for jets with radius parameter R= 1.0 , for which jets receive a dedicated calibration of the jet mass, is also discussed. © 2020, The Author(s).Ítem Emulating the impact of additional proton–proton interactions in the ATLAS simulation by presampling sets of inelastic Monte Carlo events(Springer Nature, 2022-12) Aad G.; Abbott B.; Abbott D.C.; Abud, A. Abed; Abeling K.; Abhayasinghe D.K.; Abidi S.H.; AbouZeid O.S.; Abraham N.L.; Abramowicz H.; Abreu H.; Abulaiti Y.; ;Acharya B.S.; Achkar B.; Adam L.; Bourdarios, C. Adam; Adamczyk L.; Adamek L; Adelman J.; Adiguzel A.; Adorni S.; Adye T.; Affolder A.A.; Afik Y.; Agapopoulou C.; Agaras M.N.; Aggarwal A.; Agheorghiesei C.; Aguilar-Saavedra J.A.; Ahmad A.; Ahmadov F.; Ahmed W.S.; Ai X.; Aielli G.; Akatsuka S.; Akbiyik M.; Åkesson T.P.A.; Akilli E.; Akimov A.V.; Khoury, K. Al; ;Alberghi G.L.; Albert J.; Verzini, M. J. Alconada; Alderweireldt S.; Aleksa M.; Aleksandrov I.N.; Alexa C.; Alexopoulos T.; Alfonsi A.; Alfonsi F.; Alhroob M.; Ali B.; Ali S.; Aliev M.; Alimonti G.; Allaire C.; Allbrooke B.M.M.; Allport P.P.; Aloisio A.; Hoffman, A.C AbuslemeThe 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 sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the inelastic interactions are presampled, independent of the hard scatter, and stored as combined events. Consequently, for each hard-scatter interaction, only one such presampled 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. © 2022, The Author(s).Ítem 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 (Journal of High Energy Physics, (2021), 2021, 3, (243), 10.1007/JHEP03(2021)243)(Springer Science and Business Media Deutschland GmbH, 2021-11) Aad G.; Abbott B; Abbott D.C.; Abed Abud A; Abeling K; Abhayasinghe D.K.; Abidi S.H; AbouZeid O.S.; Abraham N.L; Abramowicz H.; Abreu H.; Abulaiti YOne correction is noted for the paper, which does not affect the results reported. The right panel of figure 9 is corrected as it contained the “internal” label, giving the misleading impression on the credibility of the figure. © 2021, The Author(s).Ítem Measurement of the tt¯ production cross-section in the lepton+jets channel at s=13 TeV with the ATLAS experiment(Elsevier B.V., 2020-11) Aad G.; Abbott B.; Abbott D.C.; Abed Abud A.; Abeling K.; Abhayasinghe D.K.; Abidi S.H.; AbouZeid O.S.; Abraham N.L.; Abramowicz H.; Abreu H.; Abulaiti Y.The top anti-top quark production cross-section is measured in the lepton+jets channel using proton–proton collision data at a centre-of-mass energy of s=13 TeV collected with the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 139 fb−1. Events with exactly one charged lepton and four or more jets in the final state, with at least one jet containing b-hadrons, are used to determine the tt¯ production cross-section through a profile-likelihood fit. The inclusive cross-section is measured to be σinc=830±0.4(stat.)±36(syst.)±14(lumi.)pb with a relative uncertainty of 4.6%. The result is consistent with theoretical calculations at next-to-next-to-leading order in perturbative QCD. The fiducial tt¯ cross-section within the experimental acceptance is also measured. © 2020 The Author(s)Ítem Measurements of top-quark pair spin correlations in the eμ channel at √s=13 TeV using pp collisions in the ATLAS detector(Springer, 2020-08) Aaboud M.; Aad G.; Abbott B.; Abbott D.C.; Abdinov O.; Abud, A. Abed; Abhayasinghe D.K.; Abidi S.H.; AbouZeid O.S.; Abraham N.L.; Abramowicz H.; Abreu H.A measurement of observables sensitive to spin correlations in tt¯ production is presented, using 36.1 fb - 1 of pp collision data at 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 tt¯ 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. © 2020, CERN for the benefit of the ATLAS Collaboration.Ítem Reconstruction and identification of boosted di-τ systems in a search for Higgs boson pairs using 13 TeV proton-proton collision data in ATLAS(Springer Science and Business Media Deutschland GmbH, 2020-11) Aad G.; Abbott B.; Abbott D.C.; Abed Abud A.; Abeling K.; Abhayasinghe D.K.; Abidi S.H.; AbouZeid O.S.; Abraham N.L.; Abramowicz H.; Abreu H.; Abulaiti Y. [et al]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 bb¯ 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. [Figure not available: see fulltext.]. © 2020, The Author(s).Ítem Search for heavy diboson resonances in semileptonic final states in pp collisions at √s=13 TeV with the ATLAS detector(Springer Science and Business Media Deutschland GmbH, 2020-12) Aad G.; Abbott B.; Abbott D.C.; Abud A.A.; Abeling K.; Abhayasinghe D.K.; Abidi S.H.; AbouZeid O.S.; Abraham N.L.; Abramowicz H.; Abreu H.; Abulaiti Y.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 s=13 TeV. The data, corresponding to an integrated luminosity of 139 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. © 2020, CERN for the benefit of the ATLAS collaboration.Ítem Search for Higgs boson production in association with a high-energy photon via vector-boson fusion with decay into bottom quark pairs at √s = 13 TeV with the ATLAS detector(Springer Science and Business Media Deutschland GmbH, 2021-03) Aad G.; Abbott B.; Abbott D.C.; Abed Abud A.; Abeling K.; Abhayasinghe D.K.; Abidi S.H.; AbouZeid O.S.; Abraham N.L.; Abramowicz H.; Abreu H.; Abulaiti Y.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 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. [Figure not available: see fulltext.] © 2021, The Author(s).