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Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2024). Measurement of the t¯t¯ cross section and its ratio to the Z production cross section using pp collisions at √s=13.6 TeV with the ATLAS detector. Physics Letters B, 848, Article ID 138376.
Open this publication in new window or tab >>Measurement of the t¯t¯ cross section and its ratio to the Z production cross section using pp collisions at √s=13.6 TeV with the ATLAS detector
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2024 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 848, article id 138376Article in journal (Refereed) Published
Abstract [en]

The inclusive top-quark-pair production cross section 𝜎𝑡𝑡̄ and its ratio to the 𝑍-boson production cross section have been measured in proton–proton collisions at √𝑠 = 13.6 TeV, using 29 fb−1 of data collected in 2022 with the ATLAS experiment at the Large Hadron Collider. Using events with an opposite-charge electron-muon pair and 𝑏-tagged jets, and assuming Standard Model decays, the top-quark-pair production cross section is measured to be 𝜎𝑡𝑡̄ = 850± 3(stat.) ± 18(syst.) ± 20(lumi.) pb. The ratio of the 𝑡𝑡̄ and the 𝑍-boson production cross sections is also measured, where the 𝑍-boson contribution is determined for inclusive 𝑒+𝑒 and 𝜇+𝜇 events in a fiducial phase space. The relative uncertainty on the ratio is reduced compared to the 𝑡𝑡̄ cross section, thanks to the cancellation of several systematic uncertainties. The result for the ratio, 𝑅𝑡𝑡̄∕𝑍 = 1.145 ± 0.003(stat.) ± 0.021(syst.)±0.002(lumi.) is consistent with the Standard Model prediction using the PDF4LHC21 PDF set.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-225966 (URN)10.1016/j.physletb.2023.138376 (DOI)001136441300001 ()
Available from: 2024-01-30 Created: 2024-01-30 Last updated: 2024-01-30Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2024). Search for non-resonant production of semi-visible jets using Run 2 data in ATLAS. Physics Letters B, 848, Article ID 138324.
Open this publication in new window or tab >>Search for non-resonant production of semi-visible jets using Run 2 data in ATLAS
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2024 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 848, article id 138324Article in journal (Refereed) Published
Abstract [en]

Semi-visible jets, with a significant contribution to the event's missing transverse momentum, can arise in strongly interacting dark sectors. This results in an event topology where one of the jets can be aligned with the direction of the missing transverse momentum. The first search for semi-visible jets produced via a t-channel mediator exchange is presented. The analysis uses proton-proton collisions with an integrated luminosity of 139 fb−1 and a centre-of-mass energy of 13 TeV, collected with the ATLAS detector during the Run 2 of the LHC. No excess over Standard Model predictions is observed. Assuming a coupling strength of unity between the mediator, a Standard Model quark and a dark quark, mediator masses up to 2.7 TeV are excluded at the 95% confidence level. Upper limits on the coupling strength are also derived.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-226482 (URN)10.1016/j.physletb.2023.138324 (DOI)001127436800001 ()2-s2.0-85180280752 (Scopus ID)
Available from: 2024-02-14 Created: 2024-02-14 Last updated: 2024-02-14Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2023). A search for heavy Higgs bosons decaying into vector bosons in same-sign two-lepton final states in pp collisions at √s=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP), 2023(7), Article ID 200.
Open this publication in new window or tab >>A search for heavy Higgs bosons decaying into vector bosons in same-sign two-lepton final states in pp collisions at √s=13 TeV with the ATLAS detector
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2023 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2023, no 7, article id 200Article in journal (Refereed) Published
Abstract [en]

A search for heavy Higgs bosons produced in association with a vector boson and decaying into a pair of vector bosons is performed in final states with two leptons (electrons or muons) of the same electric charge, missing transverse momentum and jets. A data sample of proton–proton collisions at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018 is used. The data correspond to a total integrated luminosity of 139 fb−1. The observed data are in agreement with Standard Model background expectations. The results are interpreted using higher-dimensional operators in an effective field theory. Upper limits on the production cross-section are calculated at 95% confidence level as a function of the heavy Higgs boson’s mass and coupling strengths to vector bosons. Limits are set in the Higgs boson mass range from 300 to 1500 GeV, and depend on the assumed couplings. The highest excluded mass for a heavy Higgs boson with the coupling combinations explored is 900 GeV. Limits on coupling strengths are also provided.

Keywords
Higgs Physics, Hadron-Hadron Scattering, Proton-Proton Scattering
National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-223271 (URN)10.1007/JHEP07(2023)200 (DOI)001061852200001 ()
Available from: 2023-10-26 Created: 2023-10-26 Last updated: 2023-10-26Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2023). Anomaly detection search for new resonances decaying into a Higgs boson and a generic new particle X in hadronic final states using √s=13 TeV pp collisions with the ATLAS detector. Physical Review D: covering particles, fields, gravitation, and cosmology, 108(5), Article ID 052009.
Open this publication in new window or tab >>Anomaly detection search for new resonances decaying into a Higgs boson and a generic new particle X in hadronic final states using √s=13 TeV pp collisions with the ATLAS detector
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2023 (English)In: Physical Review D: covering particles, fields, gravitation, and cosmology, ISSN 2470-0010, E-ISSN 2470-0029, Vol. 108, no 5, article id 052009Article in journal (Refereed) Published
Abstract [en]

A search is presented for a heavy resonance Y decaying into a Standard Model Higgs boson H and a new particle X in a fully hadronic final state. The full Large Hadron Collider run 2 dataset of proton-proton collisions at √s=13  TeV collected by the ATLAS detector from 2015 to 2018 is used and corresponds to an integrated luminosity of 139  fb−1. The search targets the high Y-mass region, where the H and X have a significant Lorentz boost in the laboratory frame. A novel application of anomaly detection is used to define a general signal region, where events are selected solely because of their incompatibility with a learned background-only model. It is constructed using a jet-level tagger for signal-model-independent selection of the boosted X particle, representing the first application of fully unsupervised machine learning to an ATLAS analysis. Two additional signal regions are implemented to target a benchmark X decay into two quarks, covering topologies where the X is reconstructed as either a single large-radius jet or two small-radius jets. The analysis selects Higgs boson decays into , and a dedicated neural-network-based tagger provides sensitivity to the boosted heavy-flavor topology. No significant excess of data over the expected background is observed, and the results are presented as upper limits on the production cross section  for signals with mY between 1.5 and 6 TeV and mX between 65 and 3000 GeV.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-224199 (URN)10.1103/PhysRevD.108.052009 (DOI)001088448300001 ()2-s2.0-85175428199 (Scopus ID)
Available from: 2023-12-07 Created: 2023-12-07 Last updated: 2023-12-07Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2023). ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset. European Physical Journal C, 83(7), Article ID 681.
Open this publication in new window or tab >>ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset
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2023 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 83, no 7, article id 681Article in journal (Refereed) Published
Abstract [en]

The flavour-tagging algorithms developed by the ATLAS Collaboration and used to analyse its dataset of √s=13 TeV pp collisions from Run 2 of the Large Hadron Collider are presented. These new tagging algorithms are based on recurrent and deep neural networks, and their performance is evaluated in simulated collision events. These developments yield considerable improvements over previous jet-flavour identification strategies. At the 77% b-jet identification efficiency operating point, light-jet (charm-jet) rejection factors of 170 (5) are achieved in a sample of simulated Standard Model events; similarly, at a c-jet identification efficiency of 30%, a light-jet (b-jet) rejection factor of 70 (9) is obtained.

National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:su:diva-222253 (URN)10.1140/epjc/s10052-023-11699-1 (DOI)001062397400001 ()2-s2.0-85167625195 (Scopus ID)
Available from: 2023-10-13 Created: 2023-10-13 Last updated: 2023-10-13Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2023). Calibration of the light-flavour jet mistagging efficiency of the b-tagging algorithms with Z+jets events using 139 fb−1 of ATLAS proton–proton collision data at √s=13 TeV. European Physical Journal C, 83(8), Article ID 728.
Open this publication in new window or tab >>Calibration of the light-flavour jet mistagging efficiency of the b-tagging algorithms with Z+jets events using 139 fb−1 of ATLAS proton–proton collision data at √s=13 TeV
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2023 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 83, no 8, article id 728Article in journal (Refereed) Published
Abstract [en]

The identification of b-jets, referred to as b-tagging, is an important part of many physics analyses in the ATLAS experiment at the Large Hadron Collider and an accurate calibration of its performance is essential for high-quality physics results. This publication describes the calibration of the light-flavour jet mistagging efficiency in a data sample of proton–proton collision events at √s=13 TeV corresponding to an integrated luminosity of 139 fb−1. The calibration is performed in a sample of Z bosons produced in association with jets. Due to the low mistagging efficiency for light-flavour jets, a method which uses modified versions of the b-tagging algorithms referred to as flip taggers is used in this work. A fit to the jet-flavour-sensitive secondary-vertex mass is performed to extract a scale factor from data, to correct the light-flavour jet mistagging efficiency in Monte Carlo simulations, while simultaneously correcting the b-jet efficiency. With this procedure, uncertainties coming from the modeling of jets from heavy-flavour hadrons are considerably lower than in previous calibrations of the mistagging scale factors, where they were dominant. The scale factors obtained in this calibration are consistent with unity within uncertainties.

National Category
Subatomic Physics Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:su:diva-223903 (URN)10.1140/epjc/s10052-023-11736-z (DOI)001062397300002 ()2-s2.0-85168617206 (Scopus ID)
Available from: 2023-11-29 Created: 2023-11-29 Last updated: 2023-11-29Bibliographically approved
Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., Hellman, S., Milstead, D. A., . . . Strübig, A. (2023). Charged-hadron production in pp, p plus Pb, Pb plus Pb, and Xe plus Xe collisions at √sNN=5 TeV with the ATLAS detector at the LHC. Journal of High Energy Physics (JHEP) (7), Article ID 74.
Open this publication in new window or tab >>Charged-hadron production in pp, p plus Pb, Pb plus Pb, and Xe plus Xe collisions at √sNN=5 TeV with the ATLAS detector at the LHC
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2023 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, no 7, article id 74Article in journal (Refereed) Published
Abstract [en]

This paper presents measurements of charged-hadron spectra obtained in ppp+Pb, and Pb+Pb collisions at √s or √sNN = 5.02 TeV, and in Xe+Xe collisions at √sNN = 5.44 TeV. The data recorded by the ATLAS detector at the LHC have total integrated luminosities of 25 pb1, 28 nb1, 0.50 nb1, and 3 μb1, respectively. The nuclear modification factors RpPb and RAA are obtained by comparing the spectra in heavy-ion and pp collisions in a wide range of charged-particle transverse momenta and pseudorapidity. The nuclear modification factor RpPb shows a moderate enhancement above unity with a maximum at pT ≈ 3 GeV; the enhancement is stronger in the Pb-going direction. The nuclear modification factors in both Pb+Pb and Xe+Xe collisions feature a significant, centrality-dependent suppression. They show a similar distinct pT-dependence with a local maximum at pT ≈ 2 GeV and a local minimum at pT ≈ 7 GeV. This dependence is more distinguishable in more central collisions. No significant |η|-dependence is found. A comprehensive comparison with several theoretical predictions is also provided. They typically describe RAA better in central collisions and in the pT range from about 10 to 100 GeV.

Keywords
Heavy Ion Experiments
National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-223861 (URN)10.1007/JHEP07(2023)074 (DOI)001062420000001 ()2-s2.0-85165303909 (Scopus ID)
Available from: 2023-11-22 Created: 2023-11-22 Last updated: 2023-11-23Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2023). Combination of inclusive top-quark pair production cross-section measurements using ATLAS and CMS data at √s=7 and 8 TeV. Journal of High Energy Physics (JHEP), 2023(7), Article ID 213.
Open this publication in new window or tab >>Combination of inclusive top-quark pair production cross-section measurements using ATLAS and CMS data at √s=7 and 8 TeV
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2023 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2023, no 7, article id 213Article in journal (Refereed) Published
Abstract [en]

A combination of measurements of the inclusive top-quark pair production cross-section performed by ATLAS and CMS in proton–proton collisions at centre-of-mass energies of 7 and 8 TeV at the LHC is presented. The cross-sections are obtained using top-quark pair decays with an opposite-charge electron–muon pair in the final state and with data corresponding to an integrated luminosity of about 5 fb−1 at √s = 7 TeV and about 20 fb−1 at √s = 8 TeV for each experiment. The combined cross-sections are determined to be 178.5 ± 4.7 pb at √s = 7 TeV and pb at √s = 8 TeV with a correlation of 0.41, using a reference top-quark mass value of 172.5 GeV. The ratio of the combined cross-sections is determined to be R8/7 = 1.363 ± 0.032. The combined measured cross-sections and their ratio agree well with theory calculations using several parton distribution function (PDF) sets. The values of the top-quark pole mass (with the strong coupling fixed at 0.118) and the strong coupling (with the top-quark pole mass fixed at 172.5 GeV) are extracted from the combined results by fitting a next-to-next-to-leading-order plus next-to-next-to-leading-log QCD prediction to the measurements. Using a version of the NNPDF3.1 PDF set containing no top-quark measurements, the results obtained are = GeV and αs(mZ)=.

Keywords
Hadron-Hadron Scattering, Top Physics
National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-224205 (URN)10.1007/JHEP07(2023)213 (DOI)001058564200001 ()
Available from: 2023-12-06 Created: 2023-12-06 Last updated: 2023-12-06Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2023). Combination of searches for invisible decays of the Higgs boson using 139 fb−1 of proton-proton collision data at √s=13 TeV collected with the ATLAS experiment. Physics Letters B, 842, Article ID 137963.
Open this publication in new window or tab >>Combination of searches for invisible decays of the Higgs boson using 139 fb−1 of proton-proton collision data at √s=13 TeV collected with the ATLAS experiment
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2023 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 842, article id 137963Article in journal (Refereed) Published
Abstract [en]

Many extensions of the Standard Model predict the production of dark matter particles at the LHC. Sufficiently light dark matter particles may be produced in decays of the Higgs boson that would appear invisible to the detector. This Letter presents a statistical combination of searches for H→invisible decays where multiple production modes of the Standard Model Higgs boson are considered. These searches are performed with the ATLAS detector using 139 fb−1 of proton–proton collisions at a centre–of–mass energy of   at the LHC. In combination with the results at √s=7TeV and 8TeV, an upper limit on the H→invisible branching ratio of 0.107 (0.077) at the 95% confidence level is observed (expected). These results are also interpreted in the context of models where the 125 GeV Higgs boson acts as a portal to dark matter, and limits are set on the scattering cross-section of weakly interacting massive particles and nucleons.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-221774 (URN)10.1016/j.physletb.2023.137963 (DOI)001023908100001 ()2-s2.0-85163984427 (Scopus ID)
Available from: 2023-10-03 Created: 2023-10-03 Last updated: 2023-10-03Bibliographically approved
Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., Dunne, K., . . . Valdés Santurio, E. (2023). Comparison of inclusive and photon-tagged jet suppression in 5.02 TeV Pb+Pb collisions with ATLAS. Physics Letters B, 846, Article ID 138154.
Open this publication in new window or tab >>Comparison of inclusive and photon-tagged jet suppression in 5.02 TeV Pb+Pb collisions with ATLAS
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2023 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 846, article id 138154Article in journal (Refereed) Published
Abstract [en]

Parton energy loss in the quark-gluon plasma (QGP) is studied with a measurement of photon-tagged jet production in 1.7 nb-1 of Pb+Pb data and 260 pb-1 of pp data, both at root sNN = 5.02 TeV, with the ATLAS detector. The process pp -> gamma +jet+X and its analogue in Pb+Pb collisions is measured in events containing an isolated photon with transverse momentum (pT) above 50 GeV and reported as a function of jet pT. This selection results in a sample of jets with a steeply falling pT distribution that are mostly initiated by the showering of quarks. The pp and Pb+Pb measurements are used to report the nuclear modification factor, RAA, and the fractional energy loss, Sloss, for photon-tagged jets. In addition, the results are compared with the analogous ones for inclusive jets, which have a significantly smaller quark-initiated fraction. The RAA and Sloss values are found to be significantly different between those for photon-tagged jets and inclusive jets, demonstrating that energy loss in the QGP is sensitive to the colour-charge of the initiating parton. The results are also compared with a variety of theoretical models of colour-charge-dependent energy loss. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/). Funded by SCOAP3.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-226053 (URN)10.1016/j.physletb.2023.138154 (DOI)001125258300001 ()2-s2.0-85172322734 (Scopus ID)
Available from: 2024-02-12 Created: 2024-02-12 Last updated: 2024-02-12Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-3807-7831

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