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Publications (10 of 428) Show all publications
Aad, G., Andrean, S. Y., Backman, F., Bohm, C., Clement, C., Dunne, K., . . . Zwalinski, L. (2025). 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. Physics Letters B, 860, Article ID 139137.
Open this publication in new window or tab >>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
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2025 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 860, article id 139137Article in journal (Refereed) Published
Abstract [en]

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 cross-section 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.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-240507 (URN)10.1016/j.physletb.2024.139137 (DOI)001381473400001 ()2-s2.0-85210762616 (Scopus ID)
Available from: 2025-03-12 Created: 2025-03-12 Last updated: 2025-03-12Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Bohm, C., Clément, C., Dunne, K., . . . Zwalinski, L. (2025). Combination of searches for singly produced vectorlike top quarks in 𝑝⁢𝑝 collisions at √𝑠 =13  TeV with the ATLAS detector. Physical Review D: covering particles, fields, gravitation, and cosmology, 111(1), Article ID 012012.
Open this publication in new window or tab >>Combination of searches for singly produced vectorlike top quarks in 𝑝⁢𝑝 collisions at √𝑠 =13  TeV with the ATLAS detector
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2025 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 111, no 1, article id 012012Article in journal (Refereed) Published
Abstract [en]

A combination of searches for the single production of vectorlike top quarks (𝑇) is presented. These analyses are based on proton-proton collisions at √𝑠 =13  TeV recorded in 2015–2018 with the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 139  fb−1. The 𝑇 decay modes considered in this combination are into a top quark and either a Standard Model Higgs boson or a 𝑍 boson (𝑇 →𝐻⁡𝑡 and 𝑇→𝑍⁢𝑡). The individual searches used in the combination are differentiated by the number of leptons (𝑒, 𝜇) in the final state. The observed data are found to be in good agreement with the Standard Model background prediction. Interpretations are provided for a range of masses and couplings of the vectorlike top quark for benchmark models and generalized representations in terms of 95% confidence level limits. For a benchmark signal prediction of a vectorlike top quark SU(2) singlet with electroweak coupling, 𝜅, of 0.5, masses below 2.1 TeV are excluded, resulting in the most restrictive limits to date.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-240087 (URN)10.1103/PhysRevD.111.012012 (DOI)2-s2.0-85217853125 (Scopus ID)
Available from: 2025-03-07 Created: 2025-03-07 Last updated: 2025-03-07Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clement, C., . . . Zwalinski, L. (2025). Expected tracking performance of the ATLAS Inner Tracker at the High-Luminosity LHC. Journal of Instrumentation, 20(2), Article ID P02018.
Open this publication in new window or tab >>Expected tracking performance of the ATLAS Inner Tracker at the High-Luminosity LHC
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2025 (English)In: Journal of Instrumentation, Vol. 20, no 2, article id P02018Article in journal (Refereed) Published
Abstract [en]

The high-luminosity phase of LHC operations (HL-LHC), will feature a large increase in simultaneous proton-proton interactions per bunch crossing up to 200, compared with a typical leveling target of 64 in Run 3. Such an increase will create a very challenging environment in which to perform charged particle trajectory reconstruction, a task crucial for the success of the ATLAS physics program, and will exceed the capabilities of the current ATLAS Inner Detector (ID). A new all-silicon Inner Tracker (ITk) will replace the current ID in time for the start of the HL-LHC. To ensure successful use of the ITk capabilities in Run 4 and beyond, the ATLAS tracking software has been successfully adapted to achieve state-of-the-art track reconstruction in challenging high-luminosity conditions with the ITk detector. This paper presents the expected tracking performance of the ATLAS ITk based on the latest available developments since the ITk technical design reports.

Keywords
calibration, cluster finding, fitting methods, Gaseous imaging and tracking detectors, Particle tracking detectors (Solid-state detectors), Pattern recognition, Vertexing algorithms
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-242181 (URN)10.1088/1748-0221/20/02/P02018 (DOI)2-s2.0-105001207995 (Scopus ID)
Available from: 2025-04-16 Created: 2025-04-16 Last updated: 2025-04-16Bibliographically approved
Gallagher, J., Lou, X., Andrean, S. Y., Backman, F., Bohm, C., Clement, C., . . . Harkusha, S. (2025). Measurement of photonuclear jet production in ultraperipheral (Formula presented) collisions at (Formula presented) with the ATLAS detector. Physical Review D: covering particles, fields, gravitation, and cosmology, 111(5), Article ID 052006.
Open this publication in new window or tab >>Measurement of photonuclear jet production in ultraperipheral (Formula presented) collisions at (Formula presented) with the ATLAS detector
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2025 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 111, no 5, article id 052006Article in journal (Refereed) Published
Abstract [en]

In ultrarelativistic heavy ion collisions at the LHC, each nucleus acts a sources of high-energy real photons that can scatter off the opposing nucleus in ultraperipheral photonuclear ((Formula presented)) collisions. Hard scattering processes initiated by the photons in such collisions provide a novel method for probing nuclear parton distributions in a kinematic region not easily accessible to other measurements. ATLAS has measured production of dijet and multijet final states in ultraperipheral (Formula presented) collisions at (Formula presented) using a dataset recorded in 2018 with an integrated luminosity of (Formula presented). Photonuclear final states are selected by requiring a rapidity gap in the photon direction; this selects events where one of the outgoing nuclei remains intact. Jets are reconstructed using the anti-(Formula presented) algorithm with radius parameter, (Formula presented). Triple-differential cross sections, unfolded for detector response, are measured and presented using two sets of kinematic variables. The first set consists of the total transverse momentum ((Formula presented)), rapidity, and mass of the jet system. The second set uses (Formula presented) and particle-level nuclear and photon parton momentum fractions, (Formula presented) and (Formula presented), respectively. The results are compared with leading-order perturbative QCD calculations of photonuclear jet production cross sections, where all leading order predictions using existing fits fall below the data in the shadowing region. More detailed theoretical comparisons will allow these results to strongly constrain nuclear parton distributions, and these data provide results from the LHC directly comparable to early physics results at the planned Electron-Ion Collider.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-242023 (URN)10.1103/PhysRevD.111.052006 (DOI)2-s2.0-105001200288 (Scopus ID)
Available from: 2025-04-14 Created: 2025-04-14 Last updated: 2025-04-14Bibliographically approved
Zwalinski, L., Valdés Santurio, E., Strubig, A., Strandberg, S., Sjölin, J., Silverstein, S. B., . . . Aad, G. (2025). Search for a light charged Higgs boson in t→H±b decays, with H±→cs, in pp collisions at s=13TeV with the ATLAS detector. European Physical Journal C, 85(2), Article ID 153.
Open this publication in new window or tab >>Search for a light charged Higgs boson in t→H±b decays, with H±→cs, in pp collisions at s=13TeV with the ATLAS detector
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2025 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 85, no 2, article id 153Article in journal (Refereed) Published
Abstract [en]

A search for a light charged Higgs boson produced in decays of the top quark, t→H±b with H±→cs, is presented. This search targets the production of top-quark pairs tt¯→WbH±b, with W→ℓν (ℓ=e,μ), resulting in a lepton-plus-jets final state characterised by an isolated electron or muon and at least four jets. The search exploits b-quark and c-quark identification techniques as well as multivariate methods to suppress the dominant tt¯ background. The data analysed correspond to 140fb-1 of pp collisions at s=13TeV recorded with the ATLAS detector at the LHC between 2015 and 2018. Observed (expected) 95% confidence-level upper limits on the branching fraction B(t→H±b), assuming B(t→Wb)+B(t→H±(→cs)b)=1.0, are set between 0.066% (0.077%) and 3.6% (2.3%) for a charged Higgs boson with a mass between 60 and 168 GeV.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-242179 (URN)10.1140/epjc/s10052-024-13715-4 (DOI)2-s2.0-105001209933 (Scopus ID)
Available from: 2025-04-16 Created: 2025-04-16 Last updated: 2025-04-16Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2025). Search for a new scalar decaying into new spin-1 bosons in four-lepton final states with the ATLAS detector. Physics Letters B, 865, Article ID 139472.
Open this publication in new window or tab >>Search for a new scalar decaying into new spin-1 bosons in four-lepton final states with the ATLAS detector
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2025 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 865, article id 139472Article in journal (Refereed) Published
Abstract [en]

A search is conducted for a new scalar boson S, with a mass distinct from that of the Higgs boson, decaying promptly into four leptons (ℓ=e, μ) via an intermediate state containing two on-shell, promptly decaying new spin-1 bosons Zd: S→ZdZd→4ℓ, where the Zd boson has a mass between 15 and 300 GeV, and the S boson has a mass between either 30 and 115 GeV or 130 and 800 GeV. The search uses proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider with an integrated luminosity of 139 fb−1 at a centre-of-mass energy of √s=13 TeV. No significant excess above the Standard Model background expectation is observed. Upper limits at 95% confidence level are set on the production cross-section times branching ratio, σ(gg→S)×B(S→ZdZd→4ℓ), as a function of the mass of both particles, mS and mZd.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-242921 (URN)10.1016/j.physletb.2025.139472 (DOI)2-s2.0-105003470350 (Scopus ID)
Available from: 2025-05-06 Created: 2025-05-06 Last updated: 2025-05-06Bibliographically approved
Filmer, E. K., Lou, X., Andrean, S. Y., Backman, F., Bohm, C., Clement, C., . . . Valdés Santurio, E. (2025). Search for Dark Matter Produced in Association with a Dark Higgs Boson in the 𝑏⁢¯𝑏 Final State Using 𝑝⁢𝑝 Collisions at √𝑠=13  TeV with the ATLAS Detector. Physical Review Letters, 134(12), Article ID 121801.
Open this publication in new window or tab >>Search for Dark Matter Produced in Association with a Dark Higgs Boson in the 𝑏⁢¯𝑏 Final State Using 𝑝⁢𝑝 Collisions at √𝑠=13  TeV with the ATLAS Detector
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2025 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 134, no 12, article id 121801Article in journal (Refereed) Published
Abstract [en]

A search is performed for dark matter particles produced in association with a resonantly produced pair of 𝑏-quarks with 30<𝑚𝑏⁢𝑏<150  GeV using 140  fb−1 of proton-proton collisions at a center-of-mass energy of 13 TeV recorded by the ATLAS detector at the LHC. This signature is expected in extensions of the standard model predicting the production of dark matter particles, in particular those containing a dark Higgs boson 𝑠 that decays into 𝑏⁢¯𝑏. The highly boosted 𝑠 →𝑏⁢¯𝑏 topology is reconstructed using jet reclustering and a new identification algorithm. This search places stringent constraints across regions of the dark Higgs model parameter space that satisfy the observed relic density, excluding dark Higgs bosons with masses between 30 and 150 GeV in benchmark scenarios with 𝑍′ mediator masses up to 4.8 TeV at 95% confidence level.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-242572 (URN)10.1103/PhysRevLett.134.121801 (DOI)40215501 (PubMedID)2-s2.0-105001138945 (Scopus ID)
Available from: 2025-05-05 Created: 2025-05-05 Last updated: 2025-05-05Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clement, C., . . . Zwalinski, L. (2024). 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. European Physical Journal C, 84(3), Article ID 315.
Open this publication in new window or tab >>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
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2024 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 84, no 3, article id 315Article in journal (Refereed) Published
Abstract [en]

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<mℓℓ<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.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-235978 (URN)10.1140/epjc/s10052-024-12438-w (DOI)001253017600003 ()2-s2.0-85190755857 (Scopus ID)
Available from: 2024-11-26 Created: 2024-11-26 Last updated: 2024-11-26Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Bohm, C., Clément, C., Dunne, K., . . . Zwalinski, L. (2024). Accuracy versus precision in boosted top tagging with the ATLAS detector. Journal of Instrumentation, 19(8), Article ID P08018.
Open this publication in new window or tab >>Accuracy versus precision in boosted top tagging with the ATLAS detector
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2024 (English)In: Journal of Instrumentation, E-ISSN 1748-0221, Vol. 19, no 8, article id P08018Article in journal (Refereed) Published
Abstract [en]

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 √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.

Keywords
Analysis and statistical methods, Performance of High Energy Physics Detectors
National Category
Subatomic Physics Subatomic Physics
Identifiers
urn:nbn:se:su:diva-238071 (URN)10.1088/1748-0221/19/08/P08018 (DOI)001381766600001 ()2-s2.0-85203388592 (Scopus ID)
Available from: 2025-01-27 Created: 2025-01-27 Last updated: 2025-02-14Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clement, C., . . . Zwalinski, L. (2024). ATLAS Run 2 searches for electroweak production of supersymmetric particles interpreted within the pMSSM. Journal of High Energy Physics (JHEP), 2024(5), Article ID 106.
Open this publication in new window or tab >>ATLAS Run 2 searches for electroweak production of supersymmetric particles interpreted within the pMSSM
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2024 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2024, no 5, article id 106Article in journal (Refereed) Published
Abstract [en]

A summary of the constraints from searches performed by the ATLAS collaboration for the electroweak production of charginos and neutralinos is presented. Results from eight separate ATLAS searches are considered, each using 140 fb−1 of proton-proton data at a centre-of-mass energy of s = 13 TeV collected at the Large Hadron Collider during its second data-taking run. The results are interpreted in the context of the 19-parameter phenomenological minimal supersymmetric standard model, where R-parity conservation is assumed and the lightest supersymmetric particle is assumed to be the lightest neutralino. Constraints from previous electroweak, flavour and dark matter related measurements are also considered. The results are presented in terms of constraints on supersymmetric particle masses and are compared with limits from simplified models. Also shown is the impact of ATLAS searches on parameters such as the dark matter relic density and the spin-dependent and spin-independent scattering cross-sections targeted by direct dark matter detection experiments. The Higgs boson and Z boson ‘funnel regions’, where a low-mass neutralino would not oversaturate the dark matter relic abundance, are almost completely excluded by the considered constraints. Example spectra for non-excluded supersymmetric models with light charginos and neutralinos are also presented.

Keywords
Beyond Standard Model, Hadron-Hadron Scattering, Supersymmetry
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:su:diva-241299 (URN)10.1007/JHEP05(2024)106 (DOI)001280063500001 ()2-s2.0-85208419299 (Scopus ID)
Available from: 2025-03-27 Created: 2025-03-27 Last updated: 2025-03-27Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0001-7489-9184

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