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Publication Open Access Search for pair production of heavy vector-like quarks decaying into high-p T W bosons and top quarks in the lepton-plus-jets final state in pp collisions at √s=13 TeV with the ATLAS detector(Springer Verlag, 2018) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdinov, O. B.; Abeloos, Baptiste; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., National Energy Center of Nuclear Science and Technology, Rabat, Morocco; Aad, Georges, Johannes Gutenberg-Universität Mainz, Mainz, Germany; Abbott, Brad K., The Ohio State University, Columbus, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Joint Laboratory of Optics, Olomouc, Czech Republic; Abhayasinghe, D. K., Department of Experimental Particle Physics, Univerza v Ljubljani, Ljubljana, Slovenia; Abidi, Syed Hani, Graduate School of Science and Technology, Tokyo Metropolitan University, Hachioji, Japan; AbouZeid, O. S., Institut fiziki vysokikh energii, Protvino, Russian Federation; Abraham, Nicola L., SLAC National Accelerator Laboratory, Menlo Park, United States; Abramowicz, Halina, Elevter Andronikashvili Institute of Physics, Tbilisi, GeorgiaA search is presented for the pair production of heavy vector-like B quarks, primarily targeting B quark decays into a W boson and a top quark. The search is based on 36.1 fb−1 of pp collisions at s=13 TeV recorded in 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Data are analysed in the lepton-plus-jets final state, characterised by a high-transverse-momentum isolated electron or muon, large missing transverse momentum, and multiple jets, of which at least one is b-tagged. No significant deviation from the Standard Model expectation is observed. The 95% confidence level lower limit on the B mass is 1350 GeV assuming a 100% branching ratio to Wt. In the SU(2) singlet scenario, the lower mass limit is 1170 GeV. The 100% branching ratio limits are found to be also applicable to heavy vector-like X production, with charge +5/3, that decay into Wt. This search is also sensitive to a heavy vector-like B quark decaying into other final states (Zb and Hb) and thus mass limits on B production are set as a function of the decay branching ratios.[Figure not available: see fulltext.]. © 2025 Elsevier B.V., All rights reserved.Publication Open Access Measurements of b-jet tagging efficiency with the ATLAS detector using tt¯ events at √s=13 TeV(Springer Verlag, 2018) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdinov, O. B.; Abeloos, Baptiste; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., National Energy Center of Nuclear Science and Technology, Rabat, Morocco; Aad, Georges, Johannes Gutenberg-Universität Mainz, Mainz, Germany; Abbott, Brad K., The Ohio State University, Columbus, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Joint Laboratory of Optics, Olomouc, Czech Republic; Abhayasinghe, D. K., Department of Experimental Particle Physics, Univerza v Ljubljani, Ljubljana, Slovenia; Abidi, Syed Hani, Graduate School of Science and Technology, Tokyo Metropolitan University, Hachioji, Japan; AbouZeid, O. S., Institut fiziki vysokikh energii, Protvino, Russian Federation; Abraham, Nicola L., SLAC National Accelerator Laboratory, Menlo Park, United States; Abramowicz, Halina, Elevter Andronikashvili Institute of Physics, Tbilisi, GeorgiaThe efficiency to identify jets containing b-hadrons (b-jets) is measured using a high purity sample of dileptonic top quark-antiquark pairs (tt¯) selected from the 36.1 fb−1 of data collected by the ATLAS detector in 2015 and 2016 from proton-proton collisions produced by the Large Hadron Collider at a centre-of-mass energy s=13 TeV. Two methods are used to extract the efficiency from tt¯ events, a combinatorial likelihood approach and a tag-and-probe method. A boosted decision tree, not using b-tagging information, is used to select events in which two b-jets are present, which reduces the dominant uncertainty in the modelling of the flavour of the jets. The efficiency is extracted for jets in a transverse momentum range from 20 to 300 GeV, with data-to-simulation scale factors calculated by comparing the efficiency measured using collision data to that predicted by the simulation. The two methods give compatible results, and achieve a similar level of precision, measuring data-to-simulation scale factors close to unity with uncertainties ranging from 2% to 12% depending on the jet transverse momentum. © 2025 Elsevier B.V., All rights reserved.Publication Open Access Search for flavor-changing neutral currents in top quark decays t →Hc and t →Hu in multilepton final states in proton-proton collisions at √s = 13 TeV with the ATLAS detector(American Physical Society, 2018) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdinov, O. B.; Abeloos, Baptiste; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., Faculty of Science, Université Mohammed Premier Oujda, Oujda, Morocco; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., The University of Oklahoma, Norman, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan, Department of Physics, Universiti Malaya, Kuala Lumpur, Malaysia; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; 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., Santa Cruz Institute for Particle Physics, Santa Cruz, United States; Abraham, Nicola L., University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Tel Aviv University, Tel Aviv-Yafo, IsraelFlavor-changing neutral currents are not present in the Standard Model at tree level and are suppressed in loop processes by the unitarity of the Cabibbo-Kobayashi-Maskawa matrix, the corresponding rates for top quark decay processes are experimentally unobservable. Extensions of the Standard Model can generate new flavor-changing neutral current processes, leading to signals which, if observed, would be unambiguous evidence of new interactions. A data set corresponding to an integrated luminosity of 36.1 fb-1 of pp collisions at a center-of-mass energy of s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider is used to search for top quarks decaying to up or charm quarks with the emission of a Higgs boson, with subsequent Higgs boson decay to final states with at least one electron or muon. No signal is observed and limits on the branching fractions B(t→Hc)<0.16% and B(t→Hu)<0.19% at 95% confidence level are obtained (with expected limits of 0.15% in both cases). © 2025 Elsevier B.V., All rights reserved.Publication Open Access Search for resonances in the mass distribution of jet pairs with one or two jets identified as b -jets in proton-proton collisions at s =13 TeV with the ATLAS detector(American Physical Society, 2018) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdinov, O. B.; Abeloos, Baptiste; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., Faculty of Science, Université Mohammed Premier Oujda, Oujda, Morocco; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., The University of Oklahoma, Norman, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; 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., Santa Cruz Institute for Particle Physics, Santa Cruz, United States; Abraham, Nicola L., University of Sussex, Brighton, United Kingdom; Abramowicz, Halina, Tel Aviv University, Tel Aviv-Yafo, IsraelA search for new resonances decaying into jets containing b-hadrons in pp collisions with the ATLAS detector at the LHC is presented in the dijet mass range from 0.57 to 7 TeV. The data set corresponds to an integrated luminosity of up to 36.1 fb-1 collected in 2015 and 2016 at s=13 TeV. No evidence of a significant excess of events above the smooth background shape is found. Upper cross-section limits and lower limits on the corresponding signal mass parameters for several types of signal hypotheses are provided at 95% C.L. In addition, 95% C.L. upper limits are set on the cross sections for new processes that would produce Gaussian-shaped signals in the di-b-jet mass distributions. © 2025 Elsevier B.V., All rights reserved.Publication Metadata only Measurement of jet fragmentation in Pb+Pb and pp collisions at sNN =5.02 TeV with the ATLAS detector(American Physical Society, 2018) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdinov, O. B.; Abeloos, Baptiste; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., Faculty of Science, Université Mohammed Premier Oujda, Oujda, Morocco; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., The University of Oklahoma, Norman, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; 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, IsraelThis paper presents a measurement of jet fragmentation functions in 0.49 nb-1 of Pb+Pb collisions and 25 pb-1 of pp collisions at sNN=5.02 TeV collected in 2015 with the ATLAS detector at the LHC. These measurements provide insight into the jet quenching process in the quark-gluon plasma created in the aftermath of ultrarelativistic collisions between two nuclei. The modifications to the jet fragmentation functions are quantified by dividing the measurements in Pb+Pb collisions by baseline measurements in pp collisions. This ratio is studied as a function of the transverse momentum of the jet, the jet rapidity, and the centrality of the collision. In both collision systems, the jet fragmentation functions are measured for jets with transverse momentum between 126 and 398 GeV and with an absolute value of jet rapidity less than 2.1. An enhancement of particles carrying a small fraction of the jet momentum is observed, which increases with centrality and with increasing jet transverse momentum. Yields of particles carrying a very large fraction of the jet momentum are also observed to be enhanced. Between these two enhancements of the fragmentation functions a suppression of particles carrying an intermediate fraction of the jet momentum is observed in Pb+Pb collisions. A small dependence of the modifications on jet rapidity is observed. © 2025 Elsevier B.V., All rights reserved.Publication Open Access Search for charged Higgs bosons decaying via H ± → τ ± ντ in the τ+jets and τ+lepton final states with 36 fb−1 of pp collision data recorded at √s=13 TeV with the ATLAS experiment(Springer Verlag, 2018) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdinov, O. B.; Abeloos, Baptiste; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., National Energy Center of Nuclear Science and Technology, Rabat, Morocco; Aad, Georges, Johannes Gutenberg-Universität Mainz, Mainz, Germany; Abbott, Brad K., The Ohio State University, Columbus, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Joint Laboratory of Optics, Olomouc, Czech Republic; Abhayasinghe, D. K., Department of Experimental Particle Physics, Univerza v Ljubljani, Ljubljana, Slovenia; Abidi, Syed Hani, Graduate School of Science and Technology, Tokyo Metropolitan University, Hachioji, Japan; AbouZeid, O. S., Université Clermont Auvergne, Clermont-Ferrand, France; Abraham, Nicola L., SLAC National Accelerator Laboratory, Menlo Park, United States; Abramowicz, Halina, Elevter Andronikashvili Institute of Physics, Tbilisi, GeorgiaCharged Higgs bosons produced either in top-quark decays or in association with a top-quark, subsequently decaying via H± → τ±ντ, are searched for in 36.1 fb−1 of proton-proton collision data at s=13 TeV recorded with the ATLAS detector. Depending on whether the top-quark produced together with H± decays hadronically or leptonically, the search targets τ+jets and τ+lepton final states, in both cases with a hadronically decaying τ-lepton. No evidence of a charged Higgs boson is found. For the mass range of mH± = 90–2000 GeV, upper limits at the 95% confidence level are set on the production cross-section of the charged Higgs boson times the branching fraction ℬ (H±→ τ±ντ) in the range 4.2–0.0025 pb. In the mass range 90–160 GeV, assuming the Standard Model cross-section for tt¯ production, this corresponds to upper limits between 0.25% and 0.031% for the branching fraction ℬ(t→bH±)×ℬ(H±→τ±ντ).[Figure not available: see fulltext.] © 2025 Elsevier B.V., All rights reserved.Publication Open Access Prompt and non-prompt J/ ψ elliptic flow in Pb+Pb collisions at √sNN=5.02 Tev with the ATLAS detector(Springer Science and Business Media, LLC, 2018) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdinov, O. B.; Abeloos, Baptiste; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., National Energy Center of Nuclear Science and Technology, Rabat, Morocco; Aad, Georges, Johannes Gutenberg-Universität Mainz, Mainz, Germany; Abbott, Brad K., The Ohio State University, Columbus, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Joint Laboratory of Optics, Olomouc, Czech Republic; Abhayasinghe, D. K., Department of Experimental Particle Physics, Univerza v Ljubljani, Ljubljana, Slovenia; Abidi, Syed Hani, Graduate School of Science and Technology, Tokyo Metropolitan University, Hachioji, Japan; AbouZeid, O. S., Université Clermont Auvergne, Clermont-Ferrand, France; Abraham, Nicola L., SLAC National Accelerator Laboratory, Menlo Park, United States; Abramowicz, Halina, Ivane Javakhishvili Tbilisi State University, Tbilisi, GeorgiaThe elliptic flow of prompt and non-prompt J/ ψ was measured in the dimuon decay channel in Pb+Pb collisions at sNN=5.02 TeV with an integrated luminosity of 0.42nb-1 with the ATLAS detector at the LHC. The prompt and non-prompt signals are separated using a two-dimensional simultaneous fit of the invariant mass and pseudo-proper decay time of the dimuon system from the J/ ψ decay. The measurement is performed in the kinematic range of dimuon transverse momentum and rapidity 9 < pT< 30 GeV , | y| < 2 , and 0–60% collision centrality. The elliptic flow coefficient, v2, is evaluated relative to the event plane and the results are presented as a function of transverse momentum, rapidity and centrality. It is found that prompt and non-prompt J/ ψ mesons have non-zero elliptic flow. Prompt J/ ψv2 decreases as a function of pT, while for non-prompt J/ ψ it is, with limited statistical significance, consistent with a flat behaviour over the studied kinematic region. There is no observed dependence on rapidity or centrality. © 2024 Elsevier B.V., All rights reserved.Publication Open Access Observation of Higgs boson production in association with a top quark pair at the LHC with the ATLAS detector(Elsevier B.V., 2018) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdinov, O. B.; Abeloos, Baptiste; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., Faculty of Science, Université Mohammed Premier Oujda, Oujda, Morocco; Aad, Georges, Department of Physics, University of Massachusetts Amherst, Amherst, United States; Abbott, Brad K., Oklahoma State University, Stillwater, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, The University of Osaka, Suita, Japan; Abhayasinghe, D. K., Department of Physics and Astronomy, University College London, London, United Kingdom; Abidi, Syed Hani, TRIUMF, Vancouver, Canada; AbouZeid, O. S., Niels Bohr Institutet, Copenhagen, Denmark; Abraham, Nicola L., School of Physics, The University of Sydney, Sydney, Australia; Abramowicz, Halina, Aristotle University of Thessaloniki, Thessaloniki, GreeceThe observation of Higgs boson production in association with a top quark pair (tt¯H), based on the analysis of proton–proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider, is presented. Using data corresponding to integrated luminosities of up to 79.8 fb−1, and considering Higgs boson decays into bb¯, WW⁎, τ+τ−, γγ, and ZZ⁎, the observed significance is 5.8 standard deviations, compared to an expectation of 4.9 standard deviations. Combined with the tt¯H searches using a dataset corresponding to integrated luminosities of 4.5 fb−1 at 7 TeV and 20.3 fb−1 at 8 TeV, the observed (expected) significance is 6.3 (5.1) standard deviations. Assuming Standard Model branching fractions, the total tt¯H production cross section at 13 TeV is measured to be 670 ± 90 (stat.) −100 +110 (syst.) fb, in agreement with the Standard Model prediction. © 2025 Elsevier B.V., All rights reserved.Publication Open Access Search for Higgs bosons produced via vector-boson fusion and decaying into bottom quark pairs in s =13 TeV pp collisions with the ATLAS detector(American Physical Society, 2018) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdinov, O. B.; Abeloos, Baptiste; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., Faculty of Science, Université Mohammed Premier Oujda, Oujda, Morocco; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., The University of Oklahoma, Norman, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; 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., Department of Physics and Astronomy, The University of Sheffield, Sheffield, United Kingdom; Abramowicz, Halina, Tel Aviv University, Tel Aviv-Yafo, IsraelA search for the bb decay of the Standard Model Higgs boson produced through vector-boson fusion is presented. Three mutually exclusive channels are considered: two all-hadronic channels and a photon-associated channel. Results are reported from the analysis of up to 30.6 fb-1 of pp data at s=13 TeV collected with the ATLAS detector at the LHC. The measured signal strength relative to the Standard Model prediction from the combined analysis is 2.5-1.3+1.4 for inclusive Higgs boson production and 3.0-1.6+1.7 for vector-boson fusion production only. © 2025 Elsevier B.V., All rights reserved.Publication Open Access Combination of searches for heavy resonances decaying into bosonic and leptonic final states using 36 fb-1 of proton-proton collision data at s =13 TeV with the ATLAS detector(American Physical Society, 2018) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdinov, O. B.; Abeloos, Baptiste; Abhayasinghe, D. K.; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Aaboud, M., Faculty of Science, Université Mohammed Premier Oujda, Oujda, Morocco; Aad, Georges, Centre de Physique des Particules de Marseille, Marseille, France; Abbott, Brad K., The University of Oklahoma, Norman, United States; Abdinov, O. B., Azerbaijan National Academy of Sciences, Baku, Azerbaijan, Departamento de Física Teórica y del Cosmos, Universidad de Granada, Granada, Spain; Abeloos, Baptiste, Laboratoire de l'Accélérateur Linéaire, Orsay, France; 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, IsraelSearches for new heavy resonances decaying into different pairings of W, Z, or Higgs bosons, as well as directly into leptons, are presented using a data sample corresponding to 36.1 fb-1 of pp collisions at s=13 TeV collected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. Analyses selecting bosonic decay modes in the qqqq, ννqq, ℓνqq, ℓℓqq, ℓνℓν, ℓℓνν, ℓνℓℓ, ℓℓℓℓ, qqbb, ννbb, ℓνbb, and ℓℓbb final states are combined, searching for a narrow-width resonance. Likewise, analyses selecting the leptonic ℓν and ℓℓ final states are also combined. These two sets of analyses are then further combined. No significant deviation from the Standard Model predictions is observed. Three benchmark models are tested: a model predicting the existence of a new heavy scalar singlet, a simplified model predicting a heavy vector-boson triplet, and a bulk Randall-Sundrum model with a heavy spin-2 Kaluza-Klein excitation of the graviton. Cross section limits are set at the 95% confidence level using an asymptotic approximation and are compared with predictions for the benchmark models. These limits are also expressed in terms of constraints on couplings of the heavy vector-boson triplet to quarks, leptons, and the Higgs boson. The data exclude a heavy vector-boson triplet with mass below 5.5 TeV in a weakly coupled scenario and 4.5 TeV in a strongly coupled scenario, as well as a Kaluza-Klein graviton with mass below 2.3 TeV. © 2025 Elsevier B.V., All rights reserved.