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Publication Open Access Search for pair production of vector-like top quarks in events with one lepton, jets, and missing transverse momentum in √s=13 TeV pp collisions with the ATLAS detector(Springer Verlag, 2017) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdinov, O. B.; Abeloos, Baptiste; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Abreu, Henso; 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; 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, Israel; Abreu, Henso, Department of Physics, Technion - Israel Institute of Technology, Haifa, IsraelThe results of a search for vector-like top quarks using events with exactly one lepton, at least four jets, and large missing transverse momentum are reported. The search is optimised for pair production of vector-like top quarks in the Z() t + X decay channel. LHC pp collision data at a centre-of-mass energy of s=13 TeV recorded by the ATLAS detector in 2015 and 2016 are used, corresponding to an integrated luminosity of 36.1 fb−1. No significant excess over the Standard Model expectation is seen and upper limits on the production cross-section of a vector-like T quark pair as a function of the T quark mass are derived. The observed (expected) 95% CL lower limits on the T mass are 870 GeV (890 GeV) for the weak-isospin singlet model, 1.05 TeV (1.06 TeV) for the weak-isospin doublet model and 1.16 TeV (1.17 TeV) for the pure Zt decay mode. Limits are also set on the mass as a function of the decay branching ratios, excluding large parts of the parameter space for masses below 1 TeV.[Figure not available: see fulltext.]. © 2025 Elsevier B.V., All rights reserved.Publication Open Access Search for pair production of heavy vector-like quarks decaying to high-p T W bosons and b quarks in the lepton-plus-jets final state in pp collisions at √s=13 TeV with the ATLAS detector(Springer Verlag, 2017) Aaboud, M.; Aad, Georges; Abbott, Brad K.; Abdinov, O. B.; Abeloos, Baptiste; Abidi, Syed Hani; AbouZeid, O. S.; Abraham, Nicola L.; Abramowicz, Halina; Abreu, Henso; 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; 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, Israel; Abreu, Henso, Department of Physics, Technion - Israel Institute of Technology, Haifa, IsraelA search is presented for the pair production of heavy vector-like T quarks, primarily targeting the T quark decays to a W boson and a b-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, including at least one b-tagged jet and a large-radius jet identified as originating from the hadronic decay of a high-momentum W boson. No significant deviation from the Standard Model expectation is observed in the reconstructed T mass distribution. The observed 95% confidence level lower limit on the T mass are 1350 GeV assuming 100% branching ratio to Wb. In the SU(2) singlet scenario, the lower mass limit is 1170 GeV. This search is also sensitive to a heavy vector-like B quark decaying to Wt and other final states. The results are thus reinterpreted to provide a 95% confidence level lower limit on the B quark mass at 1250 GeV assuming 100% branching ratio to Wt, in the SU(2) singlet scenario, the limit is 1080 GeV. Mass limits on both T and B production are also set as a function of the decay branching ratios. The 100% branching ratio limits are found to be applicable to heavy vector-like Y and X production that decay to Wb and Wt, respectively. © 2025 Elsevier B.V., All rights reserved.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 Search for single production of vector-like quarks decaying into Wb in pp collisions at √s = 13 TeV with the ATLAS detector(Springer Verlag, 2019) 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, GeorgiaA search for singly produced vector-like quarks Q, where Q can be either a T quark with charge +2/3 or a Y quark with charge −4/3, is performed in proton–proton collision data at a centre-of-mass energy of 13 TeV corresponding to an integrated luminosity of 36.1 fb−1, recorded with the ATLAS detector at the LHC in 2015 and 2016. The analysis targets Q → Wb decays where the W boson decays leptonically. No significant deviation from the expected Standard Model background is observed. Upper limits are set on the QWb coupling strength and the mixing between the Standard Model sector and a singlet T quark or a Y quark from a (B, Y) doublet or a (T, B, Y) triplet, taking into account the interference effects with the Standard Model background. The upper limits set on the mixing angle are as small as |sin θL| = 0.18 for a singlet T quark of mass 800 GeV, |sin θR| = 0.17 for a Y quark of mass 800 GeV in a (B, Y) doublet model and |sin θL| = 0.16 for a Y quark of mass 800 GeV in a (T, B, Y) triplet model. Within a (B, Y) doublet model, the limits set on the mixing parameter |sin θR| are comparable with the exclusion limits from electroweak precision observables in the mass range between about 900 GeV and 1250 GeV.[Figure not available: see fulltext.] © 2025 Elsevier B.V., All rights reserved.