| 1. |
- Andrean, Stefio Y., et al.
(author)
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Operation of the ATLAS trigger system in Run 2
- 2020
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In: Journal of Instrumentation. - : IOP Publishing. - 1748-0221 .- 1748-0221. ; 15:10
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Journal article (peer-reviewed)abstract
- 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 presented.
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| 2. |
- Aad, G, et al.
(author)
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Alignment of the ATLAS Inner Detector in Run 2
- 2020
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:12
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Journal article (peer-reviewed)abstract
- 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).
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| 3. |
- Aad, G, et al.
(author)
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ATLAS data quality operations and performance for 2015-2018 data-taking
- 2020
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In: Journal of Instrumentation. - : Institute of Physics Publishing (IOPP). - 1748-0221. ; 15:4
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Journal article (peer-reviewed)abstract
- The ATLAS detector at the Large Hadron Collider reads out particle collision data from over 100 million electronic channels at a rate of approximately 100 kHz, with a recording rate for physics events of approximately 1 kHz. Before being certified for physics analysis at computer centres worldwide, the data must be scrutinised to ensure they are clean from any hardware or software related issues that may compromise their integrity. Prompt identification of these issues permits fast action to investigate, correct and potentially prevent future such problems that could render the data unusable. This is achieved through the monitoring of detector-level quantities and reconstructed collision event characteristics at key stages of the data processing chain. This paper presents the monitoring and assessment procedures in place at ATLAS during 2015-2018 data-taking. Through the continuous improvement of operational procedures, ATLAS achieved a high data quality efficiency, with 95.6% of the recorded proton-proton collision data collected at s=13 TeV certified for physics analysis.
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| 4. |
- Aad, G, et al.
(author)
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Evidence for tt¯ tt¯ production in the multilepton final state in proton–proton collisions at √s=13 TeV with the ATLAS detector
- 2020
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:11
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Journal article (peer-reviewed)abstract
- A search is presented for four-top-quark production using an integrated luminosity of 139 fb- 1 of proton–proton collision data at a centre-of-mass energy of 13TeV 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 24-6+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. © 2020, CERN for the benefit of the ATLAS collaboration.
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| 5. |
- Aad, G., et al.
(author)
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Higgs boson production cross-section measurements and their EFT interpretation in the 4ℓ decay channel at s√=13 TeV with the ATLAS detector
- 2020
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6052 .- 1434-6044. ; 80:10
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Journal article (peer-reviewed)abstract
- 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.
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| 6. |
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| 7. |
- Aad, G, et al.
(author)
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Measurement of isolated-photon plus two-jet production in pp collisions at √s = 13 TeV with the ATLAS detector
- 2020
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In: Journal of High Energy Physics. - : Springer. - 1029-8479 .- 1126-6708. ; 2020:3
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Journal article (peer-reviewed)abstract
- The dynamics of isolated-photon plus two-jet production in pp collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset corresponding to an integrated luminosity of 36.1 fb−1. Cross sections are measured as functions of a variety of observables, including angular correlations and invariant masses of the objects in the final state, γ + jet + jet. Measurements are also performed in phase-space regions enriched in each of the two underlying physical mechanisms, namely direct and fragmentation processes. The measurements cover the range of photon (jet) transverse momenta from 150 GeV (100 GeV) to 2 TeV. The tree-level plus parton-shower predictions from Sherpa and Pythia as well as the next-to-leading-order QCD predictions from Sherpa are compared with the measurements. The next-to-leading-order QCD predictions describe the data adequately in shape and normalisation except for regions of phase space such as those with high values of the invariant mass or rapidity separation of the two jets, where the predictions overestimate the data. [Figure not available: see fulltext.] © 2020, The Author(s).
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| 8. |
- Aad, G, et al.
(author)
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Measurement of the Lund Jet Plane Using Charged Particles in 13 TeV Proton-Proton Collisions with the ATLAS Detector
- 2020
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In: Physical Review Letters. - : American Physical Society (APS). - 1079-7114 .- 0031-9007. ; 124:22
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Journal article (peer-reviewed)abstract
- 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 sqrt[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.
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| 9. |
- Aad, G, et al.
(author)
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Measurement of the transverse momentum distribution of Drell–Yan lepton pairs in proton–proton collisions at √s=13 TeV with the ATLAS detector
- 2020
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In: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:7
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Journal article (peer-reviewed)abstract
- This paper describes precision measurements of the transverse momentum pTℓℓ (ℓ= e, μ) and of the angular variable ϕη∗ distributions of Drell–Yan lepton pairs in a mass range of 66–116 GeV. The analysis uses data from 36.1 fb- 1 of proton–proton collisions at a centre-of-mass energy of s=13TeV 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 s=7 and 8TeV, 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 pTℓℓ. 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. © 2020, CERN for the benefit of the ATLAS collaboration.
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| 10. |
- Aad, G, et al.
(author)
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Measurements of the Higgs boson inclusive and differential fiducial cross sections in the 4 ℓ decay channel at √s = 13 TeV
- 2020
-
In: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:10
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Journal article (peer-reviewed)abstract
- Inclusive and differential fiducial cross sections of the Higgs boson are measured in the H→ ZZ∗→ 4 ℓ (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 fb - 1. The inclusive fiducial cross section for the H→ ZZ∗→ 4 ℓ process is measured to be σfid= 3.28 ± 0.32 fb, in agreement with the Standard Model prediction of σfid , 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. © 2020, The Author(s).
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