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Publication Open Access Search for Heavy Higgs Bosons Decaying into Two Tau Leptons with the ATLAS Detector Using pp Collisions at s =13 TeV(American Physical Society [email protected],[email protected],[email protected],[email protected],[email protected],[email protected], 2020) Aad, Georges; Abbott, Brad K.; Abbott, D. C.; Abed Abud, Adam; Abeling, Kira; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., Department of Physics, Universidad Nacional de Colombia, Bogota, Colombia, Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abbott, D. C., Department of Physics, University of Massachusetts Amherst, Amherst, United States; Abed Abud, Adam, University Politehnica of Bucharest, Bucharest, Romania, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland; Abeling, Kira, Institute of Physics, Georg-August-Universität Göttingen, Gottingen, Germany; Abhayasinghe, D. K., Department of Physics, Royal Holloway, University of London, Egham, United Kingdom; Abidi, Syed Hani, Department of Physics, University of Toronto, Toronto, Canada; AbouZeid, O. S., Niels Bohr Institutet, Copenhagen, Denmark; Abraham, Nicola L., Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv-Yafo, IsraelA search for heavy neutral Higgs bosons is performed using the LHC Run 2 data, corresponding to an integrated luminosity of 139 fb-1 of proton-proton collisions at s=13 TeV recorded with the ATLAS detector. The search for heavy resonances is performed over the mass range 0.2-2.5 TeV for the τ+τ-decay with at least one τ-lepton decaying into final states with hadrons. The data are in good agreement with the background prediction of the standard model. In the Mh125 scenario of the minimal supersymmetric standard model, values of tanβ>8 and tanβ>21 are excluded at the 95% confidence level for neutral Higgs boson masses of 1.0 and 1.5 TeV, respectively, where tanβ is the ratio of the vacuum expectation values of the two Higgs doublets. © 2020 Elsevier B.V., All rights reserved.Publication Open Access Search for direct production of electroweakinos in final states with one lepton, missing transverse momentum and a Higgs boson decaying into two b-jets in pp collisions at √s=13 TeV with the ATLAS detector(Springer Nature, 2020) Aad, Georges; Abbott, Brad K.; Abbott, D. C.; Abed Abud, Adam; Abeling, Kira; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., The University of Oklahoma, Norman, United States; Abbott, D. C., Department of Physics, University of Massachusetts Amherst, Amherst, United States; Abed Abud, Adam, Istituto Nazionale di Fisica Nucleare, Sezione di Pavia, Pavia, Italy, Università degli Studi di Pavia, Pavia, Italy; Abeling, Kira, Georg-August-Universität Göttingen, Gottingen, Germany; Abhayasinghe, D. K., Department of Physics, Royal Holloway, University of London, Egham, United Kingdom; Abidi, Syed Hani, University of Toronto, Toronto, Canada; AbouZeid, O. S., Niels Bohr Institutet, Copenhagen, Denmark; Abraham, Nicola L., University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Tel Aviv University, Tel Aviv-Yafo, IsraelThe results of a search for electroweakino pair production pp→χ~1±χ~20 in which the chargino (χ~1±) decays into a W boson and the lightest neutralino (χ~10), while the heavier neutralino (χ~20) decays into the Standard Model 125 GeV Higgs boson and a second χ~10 are presented. The signal selection requires a pair of b-tagged jets consistent with those from a Higgs boson decay, and either an electron or a muon from the W boson decay, together with missing transverse momentum from the corresponding neutrino and the stable neutralinos. The analysis is based on data corresponding to 139 fb - 1 of s=13 TeV pp collisions provided by the Large Hadron Collider and recorded by the ATLAS detector. No statistically significant evidence of an excess of events above the Standard Model expectation is found. Limits are set on the direct production of the electroweakinos in simplified models, assuming pure wino cross-sections. Masses of χ~1±/χ~20 up to 740 GeV are excluded at 95% confidence level for a massless χ~10. © 2025 Elsevier B.V., All rights reserved.Publication Open Access CP Properties of Higgs Boson Interactions with Top Quarks in the t t ¯ H and tH Processes Using H →γγ with the ATLAS Detector(American Physical Society [email protected],[email protected],[email protected],[email protected],[email protected],[email protected], 2020) Aad, Georges; Abbott, Brad K.; Abbott, D. C.; Abed Abud, Adam; Abeling, Kira; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Aix Marseille Université, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abbott, D. C., Department of Physics, University of Massachusetts Amherst, Amherst, United States; Abed Abud, Adam, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland; Abeling, Kira, Institute of Physics, Georg-August-Universität Göttingen, Gottingen, Germany; Abhayasinghe, D. K., Department of Physics, Royal Holloway, University of London, Egham, United Kingdom; Abidi, Syed Hani, Department of Physics, University of Toronto, Toronto, Canada; AbouZeid, O. S., Niels Bohr Institutet, Copenhagen, Denmark; Abraham, Nicola L., Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv-Yafo, IsraelA study of the charge conjugation and parity (CP) properties of the interaction between the Higgs boson and top quarks is presented. Higgs bosons are identified via the diphoton decay channel (H→γγ), and their production in association with a top quark pair (tt¯H) or single top quark (tH) is studied. The analysis uses 139 fb-1 of proton-proton collision data recorded at a center-of-mass energy of s=13 TeV with the ATLAS detector at the Large Hadron Collider. Assuming a CP-even coupling, the tt¯H process is observed with a significance of 5.2 standard deviations. The measured cross section times H→γγ branching ratio is 1.64-0.36+0.38(stat)-0.14+0.17(sys) fb, and the measured rate for tt¯H is 1.43-0.31+0.33(stat)-0.15+0.21(sys) times the Standard Model expectation. The tH production process is not observed and an upper limit on its rate of 12 times the Standard Model expectation is set. A CP-mixing angle greater (less) than 43 (-43)° is excluded at 95% confidence level. © 2020 Elsevier B.V., All rights reserved.Publication Open Access Performance of the ATLAS muon triggers in Run 2(Institute of Physics, 2020) Aad, Georges; Abbott, Brad K.; Abbott, D. C.; Abed Abud, Adam; Abeling, Kira; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., The University of Oklahoma, Norman, United States; Abbott, D. C., Department of Physics, University of Massachusetts Amherst, Amherst, United States; Abed Abud, Adam, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland; Abeling, Kira, Georg-August-Universität Göttingen, Gottingen, Germany; Abhayasinghe, D. K., Department of Physics, Royal Holloway, University of London, Egham, United Kingdom; Abidi, Syed Hani, University of Toronto, Toronto, Canada; AbouZeid, O. S., Niels Bohr Institutet, Copenhagen, Denmark; Abraham, Nicola L., University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Tel Aviv University, Tel Aviv-Yafo, IsraelThe performance of the ATLAS muon trigger system is evaluated with proton-proton (pp) and heavy-ion (HI) collision data collected in Run 2 during 2015-2018 at the Large Hadron Collider. It is primarily evaluated using events containing a pair of muons from the decay of Z bosons to cover the intermediate momentum range between 26 GeV and 100 GeV. Overall, the efficiency of the single-muon triggers is about 68% in the barrel region and 85% in the endcap region. The pT range for efficiency determination is extended by using muons from decays of Jψ mesons, W bosons, and top quarks. The performance in HI collision data is measured and shows good agreement with the results obtained in pp collisions. The muon trigger shows uniform and stable performance in good agreement with the prediction of a detailed simulation. Dedicated multi-muon triggers with kinematic selections provide the backbone to beauty, quarkonia, and low-mass physics studies. The design, evolution and performance of these triggers are discussed in detail. © 2025 Elsevier B.V., All rights reserved.Publication Open Access Search for Higgs Boson Decays into a Z Boson and a Light Hadronically Decaying Resonance Using 13 TeV pp Collision Data from the ATLAS Detector(American Physical Society, 2020) Aad, Georges; Abbott, Brad K.; Abbott, D. C.; Abed Abud, Adam; Abeling, Kira; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abbott, D. C., Department of Physics, University of Massachusetts Amherst, Amherst, United States; Abed Abud, Adam, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland; Abeling, Kira, Institute of Physics, Georg-August-Universität Göttingen, Gottingen, Germany; Abhayasinghe, D. K., Department of Physics, Royal Holloway, University of London, Egham, United Kingdom; Abidi, Syed Hani, Department of Physics, University of Toronto, Toronto, Canada; AbouZeid, O. S., Niels Bohr Institutet, Copenhagen, Denmark; Abraham, Nicola L., Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv-Yafo, IsraelA search for Higgs boson decays into a Z boson and a light resonance in two-lepton plus jet events is performed, using a pp collision dataset with an integrated luminosity of 139 fb-1 collected at s=13 TeV by the ATLAS experiment at the CERN LHC. The resonance considered is a light boson with a mass below 4 GeV from a possible extended scalar sector or a charmonium state. Multivariate discriminants are used for the event selection and for evaluating the mass of the light resonance. No excess of events above the expected background is found. Observed (expected) 95% confidence-level upper limits are set on the Higgs boson production cross section times branching fraction to a Z boson and the signal resonance, with values in the range 17-340 pb (16-5+6-320-90+130 pb) for the different light spin-0 boson mass and branching fraction hypotheses, and with values of 110 and 100 pb (100-30+40 and 100-30+40 pb) for the ηc and J/ψ hypotheses, respectively. © 2020 Elsevier B.V., All rights reserved.Publication Open Access Search for Heavy Resonances Decaying into a Photon and a Hadronically Decaying Higgs Boson in pp Collisions at s =13 TeV with the ATLAS Detector(American Physical Society, 2020) Aad, Georges; Abbott, Brad K.; Abbott, D. C.; Abed Abud, Adam; Abeling, Kira; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Aix Marseille Université, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abbott, D. C., Department of Physics, University of Massachusetts Amherst, Amherst, United States; Abed Abud, Adam, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland; Abeling, Kira, Institute of Physics, Georg-August-Universität Göttingen, Gottingen, Germany; Abhayasinghe, D. K., Department of Physics, Royal Holloway, University of London, Egham, United Kingdom; Abidi, Syed Hani, Department of Physics, University of Toronto, Toronto, Canada; AbouZeid, O. S., Niels Bohr Institutet, Copenhagen, Denmark; Abraham, Nicola L., Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv-Yafo, IsraelThis Letter presents a search for the production of new heavy resonances decaying into a Higgs boson and a photon using proton-proton collision data at s=13 TeV collected by the ATLAS detector at the LHC. The data correspond to an integrated luminosity of 139 fb-1. The analysis is performed by reconstructing hadronically decaying Higgs boson (H→bb¯) candidates as single large-radius jets. A novel algorithm using information about the jet constituents in the center-of-mass frame of the jet is implemented to identify the two b quarks in the single jet. No significant excess of events is observed above the expected background. Upper limits are set on the production cross-section times branching fraction for narrow spin-1 resonances decaying into a Higgs boson and a photon in the resonance mass range from 0.7 to 4 TeV, cross-section times branching fractions are excluded between 11.6 fb and 0.11 fb at a 95% confidence level. © 2021 Elsevier B.V., All rights reserved.Publication Open Access Medium-Induced Modification of Z -Tagged Charged Particle Yields in Pb+Pb Collisions at 5.02 TeV with the ATLAS Detector(American Physical Society, 2021) Aad, Georges; Abbott, Brad K.; Abbott, D. C.; Abed Abud, Adam; Abeling, Kira; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Aix Marseille Université, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abbott, D. C., Department of Physics, University of Massachusetts Amherst, Amherst, United States; Abed Abud, Adam, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland; Abeling, Kira, Institute of Physics, Georg-August-Universität Göttingen, Gottingen, Germany; Abhayasinghe, D. K., Department of Physics, Royal Holloway, University of London, Egham, United Kingdom; Abidi, Syed Hani, Department of Physics, University of Toronto, Toronto, Canada; AbouZeid, O. S., Niels Bohr Institutet, Copenhagen, Denmark; Abraham, Nicola L., Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv-Yafo, IsraelThe yield of charged particles opposite to a Z boson with large transverse momentum (pT) is measured in 260 pb-1 of pp and 1.7 nb-1 of Pb+Pb collision data at 5.02 TeV per nucleon pair recorded with the ATLAS detector at the Large Hadron Collider. The Z boson tag is used to select hard-scattered partons with specific kinematics, and to observe how their showers are modified as they propagate through the quark-gluon plasma created in Pb+Pb collisions. Compared with pp collisions, charged-particle yields in Pb+Pb collisions show significant modifications as a function of charged-particle pT in a way that depends on event centrality and Z boson pT. The data are compared with a variety of theoretical calculations and provide new information about the medium-induced energy loss of partons in a pT regime difficult to measure through other channels. © 2021 Elsevier B.V., All rights reserved.Publication Open Access Search for Dark Matter Produced in Association with a Dark Higgs Boson Decaying into W±Wa or ZZ in Fully Hadronic Final States from s =13 TeV pp Collisions Recorded with the ATLAS Detector(American Physical Society, 2021) Aad, Georges; Abbott, Brad K.; Abbott, D. C.; Abed Abud, Adam; Abeling, Kira; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States, Full Author List Given, United States; Abbott, D. C., Department of Physics, University of Massachusetts Amherst, Amherst, United States; Abed Abud, Adam, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland, Dep Fisica and CEFITEC, Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa, Caparica, Portugal; Abeling, Kira, Institute of Physics, Georg-August-Universität Göttingen, Gottingen, Germany; Abhayasinghe, D. K., Department of Physics, Royal Holloway, University of London, Egham, United Kingdom; Abidi, Syed Hani, Department of Physics, University of Toronto, Toronto, Canada; AbouZeid, O. S., Niels Bohr Institutet, Copenhagen, Denmark; Abraham, Nicola L., Department of Physics and Astronomy, University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv-Yafo, IsraelSeveral extensions of the Standard Model predict the production of dark matter particles at the LHC. An uncharted signature of dark matter particles produced in association with VV=W±Waor ZZ pairs from a decay of a dark Higgs boson s is searched for using 139 fb-1 of pp collisions recorded by the ATLAS detector at a center-of-mass energy of 13 TeV. The s→V(qq)V(qq) decays are reconstructed with a novel technique aimed at resolving the dense topology from boosted VV pairs using jets in the calorimeter and tracking information. Dark Higgs scenarios with ms>160 GeV are excluded. © 2021 Elsevier B.V., All rights reserved.Publication Open Access Test of the universality of τ and μ lepton couplings in W-boson decays with the ATLAS detector(Nature Research, 2021) Aad, Georges; Abbott, Brad K.; Abbott, D. C.; Abed Abud, Adam; Abeling, Kira; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abbott, D. C., Department of Physics, University of Massachusetts Amherst, Amherst, United States; Abed Abud, Adam, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland; Abeling, Kira, Georg-August-Universität Göttingen, Gottingen, Germany; Abhayasinghe, D. K., Department of Physics, Royal Holloway, University of London, Egham, United Kingdom; Abidi, Syed Hani, University of Toronto, Toronto, Canada; AbouZeid, O. S., Niels Bohr Institutet, Copenhagen, Denmark; Abraham, Nicola L., University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv-Yafo, IsraelThe standard model of particle physics encapsulates our best current understanding of physics at the smallest scales. A fundamental axiom of this theory is the universality of the couplings of the different generations of leptons to the electroweak gauge bosons. The measurement of the ratio of the decay rate of W bosons to τ leptons and muons, R(τ/μ), constitutes an important test of this axiom. Using 139 fb−1 of proton–proton collisions recorded with the ATLAS detector at a centre-of-mass energy of 13 TeV, we report a measurement of this quantity from di-leptonic tt¯ events where the top quarks decay into a W boson and a bottom quark. We can distinguish muons originating from W bosons and those originating from an intermediate τ lepton through the muon transverse impact parameter and differences in the muon transverse momentum spectra. The measured value of R(τ/μ) is 0.992 ± 0.013 [± 0.007(stat) ± 0.011(syst)] and is in agreement with the hypothesis of universal lepton couplings as postulated in the standard model. This is the only such measurement from the Large Hadron Collider, so far, and obtains twice the precision of previous measurements. © 2021 Elsevier B.V., All rights reserved.Publication Open Access Performance of the ATLAS RPC detector and Level-1 muon barrel trigger at √s = 13 TeV(IOP Publishing Ltd, 2021) Aad, Georges; Abbott, Brad K.; Abbott, D. C.; Abed Abud, Adam; Abeling, Kira; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, Norman, United States; Abbott, D. C., Department of Physics, University of Massachusetts Amherst, Amherst, United States; Abed Abud, Adam, Organisation Européenne pour la Recherche Nucléaire, Geneva, Switzerland; Abeling, Kira, Georg-August-Universität Göttingen, Gottingen, Germany; Abhayasinghe, D. K., Department of Physics, Royal Holloway, University of London, Egham, United Kingdom; Abidi, Syed Hani, University of Toronto, Toronto, Canada; AbouZeid, O. S., Niels Bohr Institutet, Copenhagen, Denmark; Abraham, Nicola L., University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Tel Aviv University, Tel Aviv-Yafo, IsraelThe ATLAS experiment at the Large Hadron Collider (LHC) employs a trigger system consisting of a first-level hardware trigger (L1) and a software-based high-level trigger. The L1 muon trigger system selects muon candidates, assigns them to the correct LHC bunch crossing and classifies them into one of six transverse-momentum threshold classes. The L1 muon trigger system uses resistive-plate chambers (RPCs) to generate the muon-induced trigger signals in the central (barrel) region of the ATLAS detector. The ATLAS RPCs are arranged in six concentric layers and operate in a toroidal magnetic field with a bending power of 1.5 to 5.5 Tm. The RPC detector consists of about 3700 gas volumes with a total surface area of more than 4000 m2. This paper reports on the performance of the RPC detector and L1 muon barrel trigger using 60.8 fb-1 of proton-proton collision data recorded by the ATLAS experiment in 2018 at a centre-of-mass energy of 13 TeV. Detector and trigger performance are studied using Z boson decays into a muon pair. Measurements of the RPC detector response, efficiency, and time resolution are reported. Measurements of the L1 muon barrel trigger efficiencies and rates are presented, along with measurements of the properties of the selected sample of muon candidates. Measurements of the RPC currents, counting rates and mean avalanche charge are performed using zero-bias collisions. Finally, RPC detector response and efficiency are studied at different high voltage and front-end discriminator threshold settings in order to extrapolate detector response to the higher luminosity expected for the High Luminosity LHC. © 2021 Elsevier B.V., All rights reserved.