Examinando por Autor "Abraham, N.L."
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Ítem A search for the Zγ decay mode of the Higgs boson in pp collisions at s=13 TeV with the ATLAS detector(Elsevier B.V., 2020-10) 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 for the Zγ decay of the Higgs boson, with Z boson decays into pairs of electrons or muons is presented. The analysis uses proton–proton collision data at s = 13 TeV corresponding to an integrated luminosity of 139 fb−1 recorded by the ATLAS detector at the Large Hadron Collider. The observed data are consistent with the expected background with a p-value of 1.3%. An upper limit at 95% confidence level on the production cross-section times the branching ratio for pp→H→Zγ is set at 3.6 times the Standard Model prediction while 2.6 times is expected in the presence of the Standard Model Higgs boson. The best-fit value for the signal yield normalised to the Standard Model prediction is 2.0−0.9 +1.0 where the statistical component of the uncertainty is dominant. © 2020 The AuthorÍtem Combination of the W boson polarization measurements in top quark decays using ATLAS and CMS data at √s = 8 TeV(Springer, 2020-08) Aad, G.; Abbott, B.; Abbott, D.C.; Abed Abud, A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; Abou Zeid, O.S.; Abraham, N.L.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.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 (F0), left-handed (FL), or right-handed (FR) polarizations. The resulting combined measurements of the polarization fractions are F0 = 0.693 ± 0.014 and FL = 0.315 ± 0.011. The fraction FR is calculated from the unitarity constraint to be FR = −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 F0 (FL) with respect to the most precise single measurement. A limit on anomalous right-handed vector (VR), and left- and right-handed tensor (gL, gR) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [−0.11, 0.16] for VR, [−0.08, 0.05] for gL, and [−0.04, 0.02] for gR, at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived. [Figure not available: see fulltext.] © 2020, The Author(s).Ítem Configuration and performance of the ATLAS b-jet triggers in Run 2(Springer Science and Business Media Deutschland GmbH, 2021-12) 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.Several improvements to the ATLAS triggers used to identify jets containing b-hadrons (b-jets) were implemented for data-taking during Run 2 of the Large Hadron Collider from 2016 to 2018. These changes include reconfiguring the b-jet trigger software to improve primary-vertex finding and allow more stable running in conditions with high pile-up, and the implementation of the functionality needed to run sophisticated taggers used by the offline reconstruction in an online environment. These improvements yielded an order of magnitude better light-flavour jet rejection for the same b-jet identification efficiency compared to the performance in Run 1 (2011–2012). The efficiency to identify b-jets in the trigger, and the conditional efficiency for b-jets that satisfy offline b-tagging requirements to pass the trigger are also measured. Correction factors are derived to calibrate the b-tagging efficiency in simulation to match that observed in data. The associated systematic uncertainties are substantially smaller than in previous measurements. In addition, b-jet triggers were operated for the first time during heavy-ion data-taking, using dedicated triggers that were developed to identify semileptonic b-hadron decays by selecting events with geometrically overlapping muons and jets.Ítem Constraints on Higgs boson properties using WW∗(→ eνμν) jj production in 36.1fb-1 of √s=13 TeV pp collisions with the ATLAS detector(Institute for Ionics, 2022-07) 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.; Alonso, F.This article presents the results of two studies of Higgs boson properties using the WW∗(→ eνμν) jj final state, based on a dataset corresponding to 36.1 fb - 1 of 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 (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 aL=0.91-0.18+0.10(stat.)-0.17+0.09(syst.) and aT= 1.2 ± 0.4 (stat.)-0.3+0.2(syst.). These coupling strengths are translated into pseudo-observables, resulting in κVV=0.91-0.18+0.10(stat.)-0.17+0.09(syst.) and ϵVV=0.13-0.20+0.28 (stat.)-0.10+0.08(syst.). All results are consistent with the Standard Model predictions. © 2022, The Author(s).Ítem Dijet Resonance Search with Weak Supervision Using s =13 TeV pp Collisions in the ATLAS Detector(American Physical Society, 2020-09) 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.This Letter describes a search for narrowly resonant new physics using a machine-learning anomaly detection procedure that does not rely on signal simulations for developing the analysis selection. Weakly supervised learning is used to train classifiers directly on data to enhance potential signals. The targeted topology is dijet events and the features used for machine learning are the masses of the two jets. The resulting analysis is essentially a three-dimensional search A→BC, for mA∼O(TeV), mB,mC∼O(100 GeV) and B, C are reconstructed as large-radius jets, without paying a penalty associated with a large trials factor in the scan of the masses of the two jets. The full run 2 s=13 TeV pp collision dataset of 139 fb-1 recorded by the ATLAS detector at the Large Hadron Collider is used for the search. There is no significant evidence of a localized excess in the dijet invariant mass spectrum between 1.8 and 8.2 TeV. Cross-section limits for narrow-width A, B, and C particles vary with mA, mB, and mC. For example, when mA=3 TeV and mBâ200 GeV, a production cross section between 1 and 5 fb is excluded at 95% confidence level, depending on mC. For certain masses, these limits are up to 10 times more sensitive than those obtained by the inclusive dijet search. These results are complementary to the dedicated searches for the case that B and C are standard model bosons. © 2020 CERN.Ítem Higgs boson production cross-section measurements and their EFT interpretation in the 4 ℓ decay channel at √s= 13 TeV with the ATLAS detector(Springer Science and Business Media Deutschland GmbH, 2020-10) 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.Higgs boson properties are studied in the four-lepton decay channel (where lepton = e, μ) using 139 fb - 1 of proton–proton collision data recorded at s=13 TeV by the ATLAS experiment at the Large Hadron Collider. The inclusive cross-section times branching ratio for H→ ZZ∗ decay is measured to be 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 ± 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. © 2020, The Author(s).Ítem Jet energy scale and resolution measured in proton–proton collisions at √s=13 TeV with the ATLAS detector(Springer Science and Business Media Deutschland GmbH, 2021-08) 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.Jet energy scale and resolution measurements with their associated uncertainties are reported for jets using 36–81 fb- 1 of proton–proton collision data with a centre-of-mass energy of s=13 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-kt jet algorithm with radius parameter 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 (| η| < 1.2) vary from 1% for a wide range of high-pT jets (2502.5TeV). The relative jet energy resolution is measured and ranges from (24 ± 1.5)% at 20 GeV to (6 ± 0.5)% at 300 GeV.Ítem Longitudinal Flow Decorrelations in Xe+Xe Collisions at sNN =5.44 TeV with the ATLAS Detector(American Physical Society, 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.; Acharya, B.S.; Achkar, B.; Adachi, S.; Adam, L.; Adam Bourdarios, C.; Adamczyk, L.; Adamek, L.; Adelman, J.; Adersberger, M.; Adiguzel, A.; Adorni, S.The first measurement of longitudinal decorrelations of harmonic flow amplitudes vn for n=2-4 in Xe+Xe collisions at sNN=5.44 TeV is obtained using 3 μb-1 of data with the ATLAS detector at the LHC. The decorrelation signal for v3 and v4 is found to be nearly independent of collision centrality and transverse momentum (pT) requirements on final-state particles, but for v2 a strong centrality and pT dependence is seen. When compared with the results from Pb+Pb collisions at sNN=5.02 TeV, the longitudinal decorrelation signal in midcentral Xe+Xe collisions is found to be larger for v2, but smaller for v3. Current hydrodynamic models reproduce the ratios of the vn measured in Xe+Xe collisions to those in Pb+Pb collisions but fail to describe the magnitudes and trends of the ratios of longitudinal flow decorrelations between Xe+Xe and Pb+Pb. The results on the system-size dependence provide new insights and an important lever arm to separate effects of the longitudinal structure of the initial state from other early and late time effects in heavy-ion collisions. © 2021 CERN.Ítem Measurement of the CP-violating phase ϕs in Bs0→J/ψϕ decays in ATLAS at 13 TeV(Springer Science and Business Media Deutschland GmbH, 2021-04) Aad, G.; Abbott, B.; Abbott, D.C.; Abdinov, O.; Abud, A.A.; 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.; Adachi, S.; Adam, L.; Bourdarios, C.A.; Adamczyk, L.; Adamek, L.; Adelman, J.; Adersberger, M.; Adiguzel, A.; Adorni, S.A measurement of the Bs0→J/ψϕ decay parameters using 80.5fb-1 of integrated luminosity collected with the ATLAS detector from 13 Te proton–proton collisions at the LHC is presented. The measured parameters include the CP-violating phase ϕs, the width difference Δ Γ s between the Bs0 meson mass eigenstates and the average decay width Γ s. The values measured for the physical parameters are combined with those from 19.2fb-1 of 7 and 8 Te data, leading to the following: ϕs=-0.087±0.036(stat.)±0.021(syst.)radΔΓs=0.0657±0.0043(stat.)±0.0037(syst.)ps-1Γs=0.6703±0.0014(stat.)±0.0018(syst.)ps-1Results for ϕs and Δ Γ s are also presented as 68% confidence level contours in the ϕs–Δ Γ s plane. Furthermore the transversity amplitudes and corresponding strong phases are measured. ϕs and Δ Γ s measurements are in agreement with the Standard Model predictions. © 2021, The Author(s).Ítem Measurement of the Lund Jet Plane Using Charged Particles in 13 TeV Proton-Proton Collisions with the ATLAS Detector(American Physical Society, 2020-06) 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 prevalence of hadronic jets at the LHC requires that a deep understanding of jet formation and structure is achieved in order to reach the highest levels of experimental and theoretical precision. There have been many measurements of jet substructure at the LHC and previous colliders, but the targeted observables mix physical effects from various origins. Based on a recent proposal to factorize physical effects, this Letter presents a double-differential cross-section measurement of the Lund jet plane using 139 fb-1 of s=13 TeV proton-proton collision data collected with the ATLAS detector using jets with transverse momentum above 675 GeV. The measurement uses charged particles to achieve a fine angular resolution and is corrected for acceptance and detector effects. Several parton shower Monte Carlo models are compared with the data. No single model is found to be in agreement with the measured data across the entire plane. © 2020 CERN.Ítem Measurements of inclusive and differential cross-sections of combined tt¯ γ and tWγ production in the eμ channel at 13 TeV with the ATLAS detector(Springer, 2020-09) 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.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 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. [Figure not available: see fulltext.] © 2020, The Author(s).Ítem Measurements of the production cross-section for a Z boson in association with b-jets in proton-proton collisions at √s = 13 TeV with the ATLAS detector(Springer, 2020-07) 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.This paper presents a measurement of the production cross-section of a Z boson in association with b-jets, in proton-proton collisions at 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 pT> 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. [Figure not available: see fulltext.] © 2020, The Author(s).Ítem Muon reconstruction and identification efficiency in ATLAS using the full Run 2 pp collision data set at √s=13 TeV(Springer Science and Business Media Deutschland GmbH, 2021-07) 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.This article documents the muon reconstruction and identification efficiency obtained by the ATLAS experiment for 139 fb - 1 of pp collision data at s=13 TeV collected between 2015 and 2018 during Run 2 of the LHC. The increased instantaneous luminosity delivered by the LHC over this period required a reoptimisation of the criteria for the identification of prompt muons. Improved and newly developed algorithms were deployed to preserve high muon identification efficiency with a low misidentification rate and good momentum resolution. The availability of large samples of Z→ μμ and J/ ψ→ μμ decays, and the minimisation of systematic uncertainties, allows the efficiencies of criteria for muon identification, primary vertex association, and isolation to be measured with an accuracy at the per-mille level in the bulk of the phase space, and up to the percent level in complex kinematic configurations. Excellent performance is achieved over a range of transverse momenta from 3 GeV to several hundred GeV, and across the full muon detector acceptance of | η| < 2.7.Ítem Observation of the associated production of a top quark and a Z boson in "padding-size-4-x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">pp collisions at √s = 13 TeV with the ATLAS detector(Springer, 2020-07) 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.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 tt¯ Z and diboson production. Neural networks are used to improve the background rejection and extract the signal. The measured cross-section for tℓ+ℓ−q production, including non-resonant dilepton pairs with mℓ+ℓ−> 30 GeV, is 97 ± 13 (stat.) ± 7 (syst.) fb, consistent with the Standard Model prediction. [Figure not available: see fulltext.] © 2020, The Author(s).Ítem Operation of the ATLAS trigger system in Run 2(Institute of Physics, 2020-10) 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.; Abreu, R.; Abulaiti, Y.; Acharya, B.S.; Achkar, B.; Adam, L.; Adam, Bourdarios C.; Adamczyk, L.; Adamek, L.; Adelman, J.; Adersberger, M.; 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.; Al Khoury, K.; Alberghi, G.L.; Albert, J.; Alconada Verzini, M.J.; 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.; Allen, B.W.The ATLAS experiment at the Large Hadron Collider employs a two-level trigger system to record data at an average rate of 1 kHz from physics collisions, starting from an initial bunch crossing rate of 40 MHz. During the LHC Run 2 (2015–2018), the ATLAS trigger system operated successfully with excellent performance and flexibility by adapting to the various run conditions encountered and has been vital for the ATLAS Run-2 physics programme. For proton proton running, approximately 1500 individual event selections were included in a trigger menu which specified the physics signatures and selection algorithms used for the data-taking, and the allocated event rate and bandwidth. The trigger menu must reflect the physics goals for a given data collection period, taking into account the instantaneous luminosity of the LHC and limitations from the ATLAS detector readout, online processing farm, and offline storage. This document discusses the operation of the ATLAS trigger system during the nominal proton-proton data collection in Run 2 with examples of special data-taking runs. Aspects of software validation, evolution of the trigger selection algorithms during Run 2, monitoring of the trigger system and data quality as well as trigger configuration are presentedÍtem Optimisation of large-radius jet reconstruction for the ATLAS detector in 13 TeV proton–proton collisions(Springer Science and Business Media Deutschland GmbH, 2021-04) 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.; Acharya, B.S.; Achkar, B.; Adam, L.; Bourdarios, C.A.; Adamczyk, L.; Adamek, L.; Adelman, J.; Adersberger, M.; Adiguzel, A.; Adorni, S.; Adye, T.; Affolder, A.A.Jet substructure has provided new opportunities for searches and measurements at the LHC, and has seen continuous development since the optimization of the large-radius jet definition used by ATLAS was performed during Run 1. A range of new inputs to jet reconstruction, pile-up mitigation techniques and jet grooming algorithms motivate an optimisation of large-radius jet reconstruction for ATLAS. In this paper, this optimisation procedure is presented, and the performance of a wide range of large-radius jet definitions is compared. The relative performance of these jet definitions is assessed using metrics such as their pileup stability, ability to identify hadronically decaying W bosons and top quarks with large transverse momenta. A new type of jet input object, called a ‘unified flow object’ is introduced which combines calorimeter- and inner-detector-based signals in order to achieve optimal performance across a wide kinematic range. Large-radius jet definitions are identified which significantly improve on the current ATLAS baseline definition, and their modelling is studied using pp collisions recorded by the ATLAS detector at s=13TeV during 2017. © 2021, The Author(s).Ítem Performance of the ATLAS Level-1 topological trigger in Run 2(Institute for Ionics, 2022) Aad, G.; Abbott, B.; Abbott, D.C.; Abud, Abed A.; Abeling, K.; Abhayasinghe, D.K.; Abidi, S.H.; AbouZeid, O.S.; Abraham, N.L.; Abramowicz, H.; Abreu, H.; Abulaiti, Y.During LHC Run 2 (2015–2018) the ATLAS Level-1 topological trigger allowed efficient data-taking by the ATLAS experiment at luminosities up to 2.1× 1034 cm- 2s- 1, which exceeds the design value by a factor of two. The system was installed in 2016 and operated in 2017 and 2018. It uses Field Programmable Gate Array processors to select interesting events by placing kinematic and angular requirements on electromagnetic clusters, jets, τ-leptons, muons and the missing transverse energy. It allowed to significantly improve the background event rejection and signal event acceptance, in particular for Higgs and B-physics processes.Ítem Performance of the ATLAS muon triggers in Run 2(IOP Publishing Ltd, 2020-09) Aad, G.; Abbott, B.; Abbott, D.C.; Abud, A. Abed; Abeling, K.; Abhayasinghe, D.K.; 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.; Adersberger, M.; 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.; Åkesson, T.P.A.; Akilli, E.; Akimov, A.V.; Khoury, K. Al; Alberghi, G.L.; Albert, J.; Alconada Verzini, M.J.; 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.; Allen, B.W.; Allport, P.P.; Aloisio, A.The performance of the ATLAS muon trigger system is evaluated with proton-proton (pp) and heavy-ion (HI) collision data collected in Run 2 during 2015–2018 at the Large Hadron Collider. It is primarily evaluated using events containing a pair of muons from the decay of Z bosons to cover the intermediate momentum range between 26 GeV and 100 GeV. Overall, the efficiency of the single-muon triggers is about 68% in the barrel region and 85% in the endcap region. The pT range for efficiency determination is extended by using muons from decays of J/ψ mesons, W bosons, and top quarks. The performance in HI collision data is measured and shows good agreement with the results obtained in pp collisions. The muon trigger shows uniform and stable performance in good agreement with the prediction of a detailed simulation. Dedicated multi-muon triggers with kinematic selections provide the backbone to beauty, quarkonia, and low-mass physics studies. The design, evolution and performance of these triggers are discussed in detail.Ítem Performance of the missing transverse momentum triggers for the ATLAS detector during Run-2 data taking(Springer, 2020-08) 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 factor of four increase in the LHC luminosity, from 0.5 × 1034 cm−2s−1 to 2.0 × 1034cm−2s−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. [Figure not available: see fulltext.] © 2020, The Author(s).Ítem Search for "padding-size-4-x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">tt¯ resonances in fully hadronic final states in "padding-size-4-x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">pp collisions at √s = 13 TeV with the ATLAS detector(Springer Science and Business Media Deutschland GmbH, 2020-10) 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.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 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 "padding-size-4-x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">tt¯ 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. [Figure not available: see fulltext.] © 2020, The Author(s).