Search for flavour-changing neutral current top-quark decays t → qZ in proton-proton collisions at √s=13 TeV with the ATLAS detector
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A search for flavour-changing neutral-current processes in top-quark decays is presented. Data collected with the ATLAS detector from proton-proton collisions at the Large Hadron Collider at a centre-of-mass energy of 𝑠√=13 TeV, corresponding to an integrated luminosity of 36.1 fb−1, are analysed. The search is performed using top-quark pair events, with one top quark decaying through the t → qZ (q = u, c) flavour-changing neutral-current channel, and the other through the dominant Standard Model mode t → bW. Only Z boson decays into charged leptons and leptonic W boson decays are considered as signal. Consequently, the final-state topology is characterized by the presence of three isolated charged leptons (electrons or muons), at least two jets, one of the jets originating from a b-quark, and missing transverse momentum from the undetected neutrino. The data are consistent with Standard Model background contributions, and at 95% confidence level the search sets observed (expected) upper limits of 1.7 × 10−4 (2.4 × 10−4) on the t → uZ branching ratio and 2.4 × 10−4 (3.2 × 10−4) on the t → cZ branching ratio, constituting the most stringent limits to date.
CitationAaboud M, Aad G, Abbott B, Abdinov OBo, Abeloos B, Abidi SH, AbouZeid H, Abraham NL, Abramowicz H, Abreu H, Buanes T, Dale Ø, Eigen G, Fomin N, Lipniacka A, Martin dit Latour B, Mæland S, Stugu B, Yang Z, Zalieckas J, Bugge MK, Cameron DG, Catmore JR, Feigl S, Franconi L, Garonne V, Gjelsten BK, Gramstad E, Morisbak V, Oppen H, Ould-Saada F, Read AL, Røhne OM, Sandaker H, Serfon C, Stapnes S, Vadla KOH, Abulaiti Y, Acharya BS, Adachi S, Adamczyk L, Adelman J, Adersberger M, Adye T, Affolder AA, Afik Y, Agheorghiesei C, Aguilar Saavedra JA, Ahmadov F, Aielli G, ATLAS C. Search for flavour-changing neutral current top-quark decays t → qZ in proton-proton collisions at √s=13 TeV with the ATLAS detector. Journal of High Energy Physics (JHEP). 2018;2018:176:1-41
PublisherSpringer Berlin Heidelberg
Copyright The Author(s) 2018