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) and 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.

Search for flavour-changing neutral current top-quark decays t → qZ in proton-proton collisions at √s=13 TeV with the ATLAS detector

Farina E. M.;Fraternali M.;Introzzi G.;Livan M.;Negri A.;Rebuzzi D. M.;Rimoldi A.;Sottocornola S.;
2018-01-01

Abstract

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) and 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.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11571/1273186
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