Browsing by Author "Zwalinski, L."

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Citation - WoS: 2
Citation - Scopus: 3
Accuracy Versus Precision in Boosted Top Tagging With the Atlas Detector
(Iop Publishing Ltd, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Zwalinski, L.
The identification of top quark decays where the top quark has a large momentum transverse to the beam axis, known as top tagging, is a crucial component in many measurements of Standard Model processes and searches for beyond the Standard Model physics at the Large Hadron Collider. Machine learning techniques have improved the performance of top tagging algorithms, but the size of the systematic uncertainties for all proposed algorithms has not been systematically studied. This paper presents the performance of several machine learning based top tagging algorithms on a dataset constructed from simulated proton-proton collision events measured with the ATLAS detector at root s = 13 TeV. The systematic uncertainties associated with these algorithms are estimated through an approximate procedure that is not meant to be used in a physics analysis, but is appropriate for the level of precision required for this study. The most performant algorithms are found to have the largest uncertainties, motivating the development of methods to reduce these uncertainties without compromising performance. To enable such efforts in the wider scientific community, the datasets used in this paper are made publicly available.
Citation - WoS: 12
Citation - Scopus: 21
The Atlas Experiment at the Cern Large Hadron Collider: a Description of the Detector Configuration for Run 3
(Iop Publishing Ltd, 2024) Aad, G.; Abbott, B.; Abbott, D. C.; Abdallah, J.; Abeling, K.; Abidi, S. H.; Zwalinski, L.
The ATLAS detector is installed in its experimental cavern at Point 1 of the CERN Large Hadron Collider. During Run 2 of the LHC, a luminosity of L = 2 x 10(34) cm(-2) s(-1) was routinely achieved at the start of fills, twice the design luminosity. For Run 3, accelerator improvements, notably luminosity levelling, allow sustained running at an instantaneous luminosity of L = 2x10(34) cm(-2) s(-1) , with an average of up to 60 interactions per bunch crossing. The ATLAS detector has been upgraded to recover Run 1 single-lepton trigger thresholds while operating comfortably under Run 3 sustained pileup conditions. A fourth pixel layer 3.3 cm from the beam axis was added before Run 2 to improve vertex reconstruction and b-tagging performance. New Liquid Argon Calorimeter digital trigger electronics, with corresponding upgrades to the Trigger and Data Acquisition system, take advantage of a factor of 10 finer granularity to improve triggering on electrons, photons, taus, and hadronic signatures through increased pileup rejection. The inner muon endcap wheels were replaced by New Small Wheels with Micromegas and small-strip Thin Gap Chamber detectors, providing both precision tracking and Level-1 Muon trigger functionality. Trigger coverage of the inner barrel muon layer near one endcap region was augmented with modules integrating new thin-gap resistive plate chambers and smaller-diameter drift-tube chambers. Tile Calorimeter scintillation counters were added to improve electron energy resolution and background rejection. Upgrades to Minimum Bias Trigger Scintillators and Forward Detectors improve luminosity monitoring and enable total proton-proton cross section, diffractive physics, and heavy ion measurements. These upgrades are all compatible with operation in the much harsher environment anticipated after the High-Luminosity upgrade of the LHC and are the first steps towards preparing ATLAS for the High-Luminosity upgrade of the LHC. This paper describes the Run 3 configuration of the ATLAS detector.
Citation - WoS: 9
ATLAS Searches for Additional Scalars and Exotic Higgs Boson Decays with the LHC Run 2 Dataset
(Elsevier, 2025) Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Zwalinski, L.
This report reviews the published results of searches for possible additional scalar particles and exotic decays of the Higgs boson performed by the ATLAS Collaboration using up to 140 fb(-1) of 13 TeV proton-proton collision data collected during Run 2 of the Large Hadron Collider. Key results are examined, and observed excesses, while never statistically compelling, are noted. Constraints are placed on parameters of several models which extend the Standard Model, for example by adding one or more singlet or doublet fields, or offering exotic Higgs boson decay channels. Summaries of new searches as well as extensions of previous searches are discussed. These new results have a wider reach or attain stronger exclusion limits. New experimental techniques that were developed for these searches are highlighted. Search channels which have not yet been examined are also listed, as these provide insight into possible future areas of exploration. (c) 2024 CERN for the benefit of the ATLAS Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Citation - WoS: 6
Citation - Scopus: 10
The Atlas Trigger System for Lhc Run 3 and Trigger Performance in 2022
(Iop Publishing Ltd, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Zwalinski, L.
The ATLAS trigger system is a crucial component of the ATLAS experiment at the LHC. It is responsible for selecting events in line with the ATLAS physics programme. This paper presents an overview of the changes to the trigger and data acquisition system during the second long shutdown of the LHC, and shows the performance of the trigger system and its components in the proton-proton collisions during the 2022 commissioning period as well as its expected performance in proton-proton and heavy-ion collisions for the remainder of the third LHC data-taking period (2022-2025).
Citation - Scopus: 1
Beam-Induced Backgrounds Measured in the Atlas Detector During Local Gas Injection Into the Lhc Beam Vacuum
(Iop Publishing Ltd, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Zwalinski, L.
Inelastic beam-gas collisions at the Large Hadron Collider (LHC), within a few hundred metres of the ATLAS experiment, are known to give the dominant contribution to beam backgrounds. These are monitored by ATLAS with a dedicated Beam Conditions Monitor (BCM) and with the rate of fake jets in the calorimeters. These two methods are complementary since the BCM probes backgrounds just around the beam pipe while fake jets are observed at radii of up to several metres. In order to quantify the correlation between the residual gas density in the LHC beam vacuum and the experimental backgrounds recorded by ATLAS, several dedicated tests were performed during LHC Run 2. Local pressure bumps, with a gas density several orders of magnitude higher than during normal operation, were introduced at different locations. The changes of beam-related backgrounds, seen in ATLAS, are correlated with the local pressure variation. In addition the rates of beam-gas events are estimated from the pressure measurements and pressure bump profiles obtained from calculations. Using these rates, the efficiency of the ATLAS beam background monitors to detect beam-gas events is derived as a function of distance from the interaction point. These efficiencies and characteristic distributions of fake jets from the beam backgrounds are found to be in good agreement with results of beam-gas simulations performed with the Fluka Monte Carlo programme.
Calibration of a Soft Secondary Vertex Tagger Using Proton-Proton Collisions at √s=13 Tev With the Atlas Detector
(Amer Physical Soc, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Zwalinski, L.
Several processes studied by the ATLAS experiment at the Large Hadron Collider produce low-momentum b-flavored hadrons in the final state. This paper describes the calibration of a dedicated tagging algorithm that identifies b-flavored hadrons outside of hadronic jets by reconstructing the soft secondary vertices originating from their decays. The calibration is based on a proton-proton collision dataset at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of 140 fb(-1). Scale factors used to correct the algorithm's performance in simulated events are extracted for the b-tagging efficiency and the mistag rate of the algorithm using a data sample enriched in t (t) over bar events. Several orthogonal measurement regions are defined, binned as a function of the multiplicities of soft secondary vertices and jets containing a b-flavored hadron in the event. The mistag rate scale factors are estimated separately for events with low and high average numbers of interactions per bunch crossing. The results, which are derived from events with low missing transverse momentum, are successfully validated in a phase space characterized by high missing transverse momentum and therefore are applicable to new physics searches carried out in either phase space regime.
Citation - WoS: 2
Characterising the Higgs Boson with ATLAS Data From the LHC Run-2
(Elsevier, 2025) Aad, G.; Aakvaag, E.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Zwalinski, L.
The Higgs boson was discovered by the ATLAS and CMS Collaborations in 2012 using data from Run 1 of the Large Hadron Collider (2010-2012). In Run 2 (2015-2018), about 140 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13 TeV were collected by the ATLAS experiment. This review presents the most important Run 2 results obtained by the ATLAS Collaboration regarding the properties of the Higgs boson and its interactions with other particles. The performed studies significantly enhance the understanding of the Higgs boson, while hunting for deviations from the predictions of the Standard Model of particle physics. (c) 2024 CERN for the benefit of the ATLAS Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Charged-Hadron and Identified-Hadron (Ks0, Λ, Ξ-) Yield Measurements in Photonuclear Pb Plus Pb and P Plus Pb Collisions at √snn=5.02 Tev with ATLAS
(Amer Physical Soc, 2025) Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Zwalinski, L.
This paper presents the measurement of charged-hadron and identified-hadron (K-S(0), Lambda, Xi(-)) yields in photonuclear collisions using 1.7 nb(-1) of root s(NN) = 5.02 TeV Pb + Pb data collected in 2018 with the ATLAS detector at the Large Hadron Collider. Candidate photonuclear events are selected using a combination of tracking and calorimeter information, including the zero-degree calorimeter. The yields as a function of transverse momentum and rapidity are measured in these photonuclear collisions as a function of charged-particle multiplicity. These photonuclear results are compared with 0.1nb(-1) of root s(NN) = 5.02 TeV p + Pb data collected in 2016 by ATLAS using similar charged-particle multiplicity selections. These photonuclear measurements shed light on potential quark-gluon plasma formation in photonuclear collisions via observables sensitive to radial flow, enhanced baryon-to-meson ratios, and strangeness enhancement. The results are also compared with the Monte Carlo DPMJET-III generator and hydrodynamic calculations to test whether such photonuclear collisions may produce small droplets of quark-gluon plasma that flow collectively.
Citation - WoS: 4
Citation - Scopus: 6
Combination and Summary of Atlas Dark Matter Searches Interpreted in a 2hdm With a Pseudo-Scalar Mediator Using 139 Fb^-1 of √s=13 Tev pp Collision Data
(Elsevier, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Zwalinski, L.
Results from a wide range of searches targeting different experimental signatures with and without missing transverse momentum (E-T(miss)) are used to constrain a Two-Higgs-Doublet Model (2HDM) with an additional pseudo-scalar mediating the interaction between ordinary and dark matter (2HDM+a). The analyses use up to 139 fb(-1) of proton-proton collision data at a centre-of-mass energy root s = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider during 2015-2018. The results from three of the most sensitive searches are combined statistically. These searches target signatures with large E-T(miss) and a leptonically decaying Z boson; large E-T(miss) and a Higgs boson decaying to bottom quarks; and production of charged Higgs bosons in final states with top and bottom quarks, respectively. Constraints are derived for several common and new benchmark scenarios in the 2HDM+a. (c) 2024 Science China Press. Published by Elsevier B.V. and Science China Press. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Citation - WoS: 1
Citation - Scopus: 2
Combination of Searches for Higgs Boson Decays Into a Photon and a Massless Dark Photon Using Pp Collisions at √s = 13 Tev With the Atlas Detector
(Springer, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Zwalinski, L.
A combination of searches for Higgs boson decays into a visible photon and a massless dark photon (H -> gamma gamma(d)) is presented using 139 fb(-1) of proton-proton collision data at a centre-of-mass energy of root s = 13 TeV recorded by the ATLAS detector at the Large Hadron Collider. The observed (expected) 95% confidence level upper limit on the Standard Model Higgs boson decay branching ratio is determined to be B(H -> gamma gamma(d)) < 1.3% (1.5)%. The search is also sensitive to higher-mass Higgs bosons decaying into the same final state. The observed (expected) 95% confidence level limit on the cross-section times branching ratio ranges from 16 fb (20 fb) for m(H) = 400 GeV to 1.0 fb (1.5 fb) for m(H) = 3 TeV. Results are also interpreted in the context of a minimal simplified model.
Citation - WoS: 11
Combination of Searches for Higgs Boson Pair Production in pp Collisions at √s=13 Tev With the Atlas Detector
(Amer Physical Soc, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Zwalinski, L.
This Letter presents results from a combination of searches for Higgs boson pair production using 126-140 fb(-1) of proton-proton collision data at root s = 13 TeV recorded with the ATLAS detector. At 95% confidence level (CL), the upper limit on the production rate is 2.9 times the standard model (SM) prediction, with an expected limit of 2.4 assuming no Higgs boson pair production. Constraints on the Higgs boson self-coupling modifier kappa(lambda) =lambda(HHH) /lambda(SM)(HHH), and the quartic HHVV coupling modifier kappa(2V) = g(HHVV)/g(HHVV)(SM), are derived individually, fixing the other parameter to its SM value. The observed 95% CL intervals are -1.2
Citation - WoS: 3
Citation - Scopus: 3
Combination of Searches for Singly and Doubly Charged Higgs Bosons Produced Via Vector-Boson Fusion in Proton-Proton Collisions at √s=13 Tev With the Atlas Detector
(Elsevier, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Zwalinski, L.
A combination of searches for singly and doubly charged Higgs bosons, H-+/- and H-+/-+/-, produced via vector-boson fusion is performed using 140 fb(-1) of proton-proton collisions at a centre-of-mass energy of 13 TeV, collected with the ATLAS detector during Run 2 of the Large Hadron Collider. Searches targeting decays to massive vector bosons in leptonic final states (electrons or muons) are considered. New constraints are reported on the production crosssection times branching fraction for charged Higgs boson masses between 200 GeV and 3000 GeV. The results are interpreted in the context of the Georgi-Machacek model for which the most stringent constraints to date are set for the masses considered in the combination.
Citation - WoS: 7
Citation - Scopus: 9
Constraints on Simplified Dark Matter Models Involving an s-channel Mediator With the Atlas Detector in pp Collisions at √s=13 Tev
(Springer, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Zwalinski, L.; Sultansoy, Saleh
This paper reports a summary of searches for a fermionic dark matter candidate in the context of theoretical models characterised by a mediator particle exchange in the s-channel. The data sample considered consists of pp collisions delivered by the Large Hadron Collider during its Run 2 at a centre-of-mass energy of root s = 13 TeV and recorded by the ATLAS detector, corresponding to up to 140 fb(-1). The interpretations of the results are based on simplified models where the new mediator particles can be spin-0, with scalar or pseudo-scalar couplings to fermions, or spin-1, with vector or axial-vector couplings to fermions. Exclusion limits are obtained from various searches characterised by final states with resonant production of Standard Model particles, or production of Standard Model particles in association with large missing transverse momentum.
A Continuous Calibration of the Atlas Flavour-Tagging Classifiers Via Optimal Transportation Maps
(Springer Nature, 2025) Zwalinski, L.; Zou, W.; Zormpa, O.; Zorbas, T.G.; Zoch, K.; Zoccoli, A.; Aad, G.
A calibration of the ATLAS flavour-tagging algorithms using a new calibration procedure based on optimal transportation maps is presented. Simultaneous, continuous corrections to the b-jet, c-jet, and light-flavour jet classification probabilities from jet-tagging algorithms in simulation are derived for b-jets using tt¯→eμννbb data. After application of the derived calibration maps, closure between simulation and observation is achieved for jet flavour observables used in ATLAS analyses of Large Hadron Collider (LHC) Run 2 proton-proton collision data. This continuous calibration opens up new possibilities for the future use of jet flavour information in LHC analyses and also serves as a guide for deriving high-dimensional corrections to simulation via transportation maps, an important development for a broad range of inference tasks. © CERN for the benefit of the ATLAS Collaboration 2025.
Citation - Scopus: 3
Determination of the Relative Sign of the Higgs Boson Couplings To w and z Bosons Using wh Production Via Vector-Boson Fusion With the Atlas Detector
(Amer Physical Soc, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Zwalinski, L.; Sultansoy, Saleh
The associated production of Higgs and W bosons via vector-boson fusion is highly sensitive to the relative sign of the Higgs boson couplings to W and Z bosons. In this Letter, two searches for this process are presented, using 140 fb(-1) of proton-proton collision data at root s = 13 TeV recorded by the ATLAS detector at the LHC. The first search targets scenarios with opposite-sign couplings of the W and Z bosons to the Higgs boson, while the second targets standard model-like scenarios with same-sign couplings. Both analyses consider Higgs boson decays into a pair of b quarks and W boson decays with an electron or muon. The data exclude the opposite-sign coupling hypothesis with a significance beyond 5 sigma, and the observed (expected) upper limit set on the cross section for vector-boson fusion WH production is 9.0 (8.7) times the standard model value at 95% confidence level.
Citation - WoS: 5
Citation - Scopus: 7
Differential Cross-Sections for Events With Missing Transverse Momentum and Jets Measured With the Atlas Detector in 13 Tev Proton-Proton Collisions
(Springer, 2024) Aad, G.; Aakvaag, E.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Zwalinski, L.
Measurements of inclusive, differential cross-sections for the production of events with missing transverse momentum in association with jets in proton-proton collisions at root s = 13 TeV are presented. The measurements are made with the ATLAS detector using an integrated luminosity of 140 fb(-1) and include measurements of dijet distributions in a region in which vector-boson fusion processes are enhanced. They are unfolded to correct for detector resolution and efficiency within the fiducial acceptance, and are designed to allow robust comparisons with a wide range of theoretical predictions. A measurement of differential cross sections for the Z -> nu nu process is made. The measurements are generally well-described by Standard Model predictions except for the dijet invariant mass distribution. Auxiliary measurements of the hadronic system recoiling against isolated leptons, and photons, are also made in the same phase space. Ratios between the measured distributions are then derived, to take advantage of cancellations in modelling effects and some of the major systematic uncertainties. These measurements are sensitive to new phenomena, and provide a mechanism to easily set constraints on phenomenological models. To illustrate the robustness of the approach, these ratios are compared with two common Dark Matter models, where the constraints derived from the measurement are comparable to those set by dedicated detector-level searches.
Citation - WoS: 26
Citation - Scopus: 29
Electron and Photon Efficiencies in Lhc Run 2 With the Atlas Experiment
(Springer, 2024) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N. J.; Abidi, S. H.; Aboulhorma, A.; Zwalinski, L.
Precision measurements of electron reconstruction, identification, and isolation efficiencies and photon identification efficiencies are presented. They use the full Run 2 data sample collected by the ATLAS experiment in pp collisions at a centre-of-mass energy of 13 TeV during the years 2015-2018, corresponding to an integrated luminosity of 139 fb(-1). The measured electron identification efficiencies have uncertainties that are around 30%-50% smaller than the previous Run 2 results due to an improved methodology and the inclusion of more data. A better pile-up subtraction method leads to electron isolation efficiencies that are more independent of the amount of pile-up activity. Updated photon identification efficiencies are also presented, using the full Run 2 data. When compared to the previous measurement, a 30%-40% smaller uncertainty is observed on the photon identification efficiencies, thanks to the increased amount of available data.
Citation - WoS: 2
Citation - Scopus: 2
Electroweak, QCD and Flavour Physics Studies With ATLAS Data From Run 2 of the LHC
(Elsevier, 2025) Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Zwalinski, L.
A summary of precision measurements sensitive to electroweak, QCD and quark-flavour effects performed by the ATLAS Collaboration at the Large Hadron Collider is reported. The measurements are predominantly performed on proton-proton (pp) collision data recorded at a centre-of-mass energy of 13 TeV taken from 2015 to 2018, with an integrated luminosity of up to 140 fb(-1), with some results based on pp and Pb+Pb data recorded at lower nucleon centre-of-mass energies. The results cover a wide range of topics, from strong production of particles at low energies and the spectroscopy of hadrons to perturbative QCD with hadronic jets and electroweak and strong production of single and multiple vector bosons. They provide precise measurements of fundamental constants and stringent tests of the Standard Model with unprecedented precision and in energy ranges never explored before. They are also used to explore the proton structure and to perform model-independent searches for new physics. (c) 2024 CERN for the benefit of the ATLAS Collaboration. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
Erratum: Measurement of the Total and Differential Cross-Sections of (Formula Presented.) Production in pp Collisions at (Formula Presented.) = 13 TeV with the ATLAS Detector (Journal of High Energy Physics, (2024), 2024, 5, (131), 10.1007/Jhep05(2024)131)
(Springer Science and Business Media Deutschland GmbH, 2025) Aad, G.; Abbott, B.; Abeling, K.; Abicht, N.J.; Abidi, S.H.; Aboulhorma, A.; Zwalinski, L.
On the original published paper the symbol l was not rendered correctly in following plots: • Figure 4: x-axis names • Figures 5(a)–5(d): region name • Figures 2, 3, 10(a) and 10(b): x-axis and region names The originally published wrong file has been replaced online. © 2025 The Author(s).
Citation - Scopus: 1
Evidence for Longitudinally Polarized W Bosons in the Electroweak Production of Same-Sign W Boson Pairs in Association With Two Jets in PP Collisions at √s=13 TeV With the ATLAS Detector
(Amer Physical Soc, 2025) Aad, G.; Aakvaag, E.; Abbott, B.; Abdelhameed, S.; Abeling, K.; Abicht, N. J.; Zwalinski, L.
This Letter reports the first evidence of electroweak production of same-signW boson pairs where at least one of theW bosons is longitudinally polarized and the most stringent constraint to date for the production of two longitudinally polarized same-sign W bosons. The dataset used corresponds to an integrated luminosity of 140 fb(-1) of proton-proton collisions at a center-of-mass energy of 13 TeV, collected with the ATLAS detector during run 2 of the Large Hadron Collider. The study is performed in final states including two same-sign leptons (electrons or muons), missing transverse momentum, and at least two jets with a large invariant mass and a large rapidity difference. Two independent fits are performed targeting the production of same-signW bosons with at least one, or two longitudinally polarizedW bosons. The observed (expected) significance of the production with at least one longitudinally polarized W boson is 3.3 (4.0) standard deviations. An observed (expected) 95% confidence level upper limit of 0.45 (0.70) fb is reported on the fiducial production cross section of two longitudinally polarized same-sign W bosons.