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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
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). Constraints on the Higgs boson self-coupling from single- and double-Higgs production with the ATLAS detector using pp collisions at √s=13 TeV. Physics Letters B, 843, Article ID 137745.
Open this publication in new window or tab >>Constraints on the Higgs boson self-coupling from single- and double-Higgs production with the ATLAS detector using pp collisions at √s=13 TeV
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2023 (English)In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 843, article id 137745Article in journal (Refereed) Published
Abstract [en]

Constraints on the Higgs boson self-coupling are set by combining double-Higgs boson analyses in the b¯bb¯b, b¯bτ +τ and b¯bγγ decay channels with single-Higgs boson analyses targeting the γγ , Z Z, W W , τ +τ − and b¯b decay channels. The data used in these analyses were recorded by the ATLAS detector at the LHC in proton–proton collisions at √s = 13 TeV and correspond to an integrated luminosity of 126–139 fb−1. The combination of the double-Higgs analyses sets an upper limit of μH H < 2.4 at 95% confidence level on the double-Higgs production cross-section normalised to its Standard Model prediction. Combining the single-Higgs and double-Higgs analyses, with the assumption that new physics affects only the Higgs boson self-coupling (λHHH ), values outside the interval −0.4 < κλ = (λHHH ) < 6.3 are excluded at 95% confidence level. The combined single-Higgs and double-Higgs analyses provide results with fewer assumptions, by adding in the fit more coupling modifiers introduced to account for the Higgs boson interactions with the other Standard Model particles. In this relaxed scenario, the constraint becomes −1.4 < κλ < 6.1 at 95% CL

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-221629 (URN)10.1016/j.physletb.2023.137745 (DOI)001037066800001 ()2-s2.0-85164519627 (Scopus ID)
Available from: 2023-09-27 Created: 2023-09-27 Last updated: 2023-09-27Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2023). Correlations between flow and transverse momentum in Xe+Xe and Pb+Pb collisions at the LHC with the ATLAS detector: A probe of the heavy-ion initial state and nuclear deformation. Physical Review C: Covering Nuclear Physics, 107(5), Article ID 054910.
Open this publication in new window or tab >>Correlations between flow and transverse momentum in Xe+Xe and Pb+Pb collisions at the LHC with the ATLAS detector: A probe of the heavy-ion initial state and nuclear deformation
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2023 (English)In: Physical Review C: Covering Nuclear Physics, ISSN 2469-9985, E-ISSN 2469-9993, Vol. 107, no 5, article id 054910Article in journal (Refereed) Published
Abstract [en]

The correlations between flow harmonics vn for n=2, 3, and 4 and mean transverse momentum [pT] in 129Xe+129Xe and 208Pb+208Pb collisions at √s=5.44 and 5.02 TeV, respectively, are measured using charged particles with the ATLAS detector. The correlations are potentially sensitive to the shape and size of the initial geometry, nuclear deformation, and initial momentum anisotropy. The effects from nonflow and centrality fluctuations are minimized, respectively, via a subevent cumulant method and an event-activity selection based on particle production at very forward rapidity. The vn−[pT] correlations show strong dependencies on centrality, harmonic number n, pT, and pseudorapidity range. Current models qualitatively describe the overall centrality- and system-dependent trends but fail to quantitatively reproduce all features of the data. In central collisions, where models generally show good agreement, the v2−[pT] correlations are sensitive to the triaxiality of the quadruple deformation. Comparison of the model with the Pb+Pb and Xe+Xe data confirms that the 129Xe nucleus is a highly deformed triaxial ellipsoid that has neither a prolate nor oblate shape. This provides strong evidence for a triaxial deformation of the 129Xe nucleus from high-energy heavy-ion collisions.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-221773 (URN)10.1103/PhysRevC.107.054910 (DOI)001021700000001 ()2-s2.0-85164169793 (Scopus ID)
Available from: 2023-10-03 Created: 2023-10-03 Last updated: 2023-10-03Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2023). Cross-section measurements for the production of a Z boson in association with high-transverse-momentum jets in pp collisions at √s = 13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP), 2023(6), Article ID 80.
Open this publication in new window or tab >>Cross-section measurements for the production of a Z boson in association with high-transverse-momentum jets 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 6, article id 80Article in journal (Refereed) Published
Abstract [en]

Cross-section measurements for a Z boson produced in association with high-transverse-momentum jets (pT ≥ 100 GeV) and decaying into a charged-lepton pair (e+e, μ+μ) are presented. The measurements are performed using proton–proton collisions at √s = 13 TeV corresponding to an integrated luminosity of 139 fb−1 collected by the ATLAS experiment at the LHC. Measurements of angular correlations between the Z boson and the closest jet are performed in events with at least one jet with pT ≥ 500 GeV. Event topologies of particular interest are the collinear emission of a Z boson in dijet events and a boosted Z boson recoiling against a jet. Fiducial cross sections are compared with state-of-the-art theoretical predictions. The data are found to agree with next-to-next-to-leading-order predictions by NNLOᴊᴇᴛ and with the next-to-leading-order multi-leg generators MADGRAPH5_AMC@NLO and SHERPA.

Keywords
Electroweak Interaction, Hadron-Hadron Scattering
National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-221775 (URN)10.1007/JHEP06(2023)080 (DOI)001035282400001 ()2-s2.0-85163163392 (Scopus ID)
Available from: 2023-10-03 Created: 2023-10-03 Last updated: 2023-10-03Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2023). Differential tt¯ cross-section measurements using boosted top quarks in the all-hadronic final state with 139 fb−1 of ATLAS data. Journal of High Energy Physics (JHEP), 2023(4), Article ID 080.
Open this publication in new window or tab >>Differential tt¯ cross-section measurements using boosted top quarks in the all-hadronic final state with 139 fb1 of ATLAS data
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2023 (English)In: Journal of High Energy Physics (JHEP), ISSN 1126-6708, E-ISSN 1029-8479, Vol. 2023, no 4, article id 080Article in journal (Refereed) Published
Abstract [en]

Measurements of single-, double-, and triple-differential cross-sections are presented for boosted top-quark pair-production in 13 TeV proton–proton collisions recorded by the ATLAS detector at the LHC. The top quarks are observed through their hadronic decay and reconstructed as large-radius jets with the leading jet having transverse momentum (pT) greater than 500 GeV. The observed data are unfolded to remove detector effects. The particle-level cross-section, multiplied by the branching fraction and measured in a fiducial phase space defined by requiring the leading and second-leading jets to have pT > 500 GeV and pT > 350 GeV, respectively, is 331 ± 3(stat.) ± 39(syst.) fb. This is approximately 20% lower than the prediction of fb by POWHEG+PYTHIA 8 with next-to-leading-order (NLO) accuracy but consistent within the theoretical uncertainties. Results are also presented at the parton level, where the effects of top-quark decay, parton showering, and hadronization are removed such that they can be compared with fixed-order next-to-next-to-leading-order (NNLO) calculations. The parton-level cross-section, measured in a fiducial phase space similar to that at particle level, is 1.94 ± 0.02(stat.) ± 0.25(syst.) pb. This agrees with the NNLO prediction of pb. Reasonable agreement with the differential cross-sections is found for most NLO models, while the NNLO calculations are generally in better agreement with the data. The differential cross-sections are interpreted using a Standard Model effective field-theory formalism and limits are set on Wilson coefficients of several four-fermion operators.

Keywords
Hadron-Hadron Scattering, Jet Substructure and Boosted Jets, Top Physics
National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-221779 (URN)10.1007/JHEP04(2023)080 (DOI)001022682600001 ()2-s2.0-85156104827 (Scopus ID)
Available from: 2023-10-02 Created: 2023-10-02 Last updated: 2023-10-02Bibliographically approved
Aad, G., Andrean, S. Y., Backman, F., Barranco Navarro, L., Bohm, C., Clément, C., . . . Zwalinski, L. (2023). Evidence for the charge asymmetry in pp → tt- production at √s=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP), 2023(8), Article ID 77.
Open this publication in new window or tab >>Evidence for the charge asymmetry in pp → tt- production 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 8, article id 77Article in journal (Refereed) Published
Abstract [en]

Inclusive and differential measurements of the top–antitop () charge asymmetry and the leptonic asymmetry are presented in proton–proton collisions at √s = 13 TeV recorded by the ATLAS experiment at the CERN Large Hadron Collider. The measurement uses the complete Run 2 dataset, corresponding to an integrated luminosity of 139 fb−1, combines data in the single-lepton and dilepton channels, and employs reconstruction techniques adapted to both the resolved and boosted topologies. A Bayesian unfolding procedure is performed to correct for detector resolution and acceptance effects. The combined inclusive charge asymmetry is measured to be = 0.0068 ± 0.0015, which differs from zero by 4.7 standard deviations. Differential measurements are performed as a function of the invariant mass, transverse momentum and longitudinal boost of the system. Both the inclusive and differential measurements are found to be compatible with the Standard Model predictions, at next-to-next-to-leading order in quantum chromodynamics perturbation theory with next-to-leading-order electroweak corrections. The measurements are interpreted in the framework of the Standard Model effective field theory, placing competitive bounds on several Wilson coefficients.

Keywords
Hadron-Hadron Scattering, Top Physics
National Category
Subatomic Physics
Identifiers
urn:nbn:se:su:diva-223710 (URN)10.1007/JHEP08(2023)077 (DOI)001062398000001 ()2-s2.0-85169322582 (Scopus ID)
Available from: 2023-11-17 Created: 2023-11-17 Last updated: 2023-11-17Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-7644-5984

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