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



Aaboud, M, Aad, G, Abbott, B, Abdinov, O, Abeloos, B, Abidi, SH, AbouZeid, OS, Abraham, NL, Abramowicz, H, Abreu, H
et al (show 2859 more authors) (2018) Search for flavour-changing neutral current top-quark decays <i>t</i> → <i>qZ</i> in proton-proton collisions at √<i>s</i>=13 TeV with the ATLAS detector. JOURNAL OF HIGH ENERGY PHYSICS, 07 (7). 176-.

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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 $\sqrt{s}=13$ 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 $t\rightarrow qZ$ $(q = u, c)$ flavour-changing neutral-current channel, and the other through the dominant Standard Model mode $t\rightarrow bW$. 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 $1.7\times10^{-4}$ ($2.4\times10^{-4}$) on the $t\to uZ$ branching ratio and $2.4\times10^{-4}$ ($3.2\times10^{-4}$) on the $t\to cZ$ branching ratio, constituting the most stringent limits to date.

Item Type: Article
Additional Information: 42 pages in total, author list starting page 26, 4 figures, 11 tables, published in JHEP. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2017-06
Uncontrolled Keywords: Hadron-Hadron scattering (experiments)
Depositing User: Symplectic Admin
Date Deposited: 10 Sep 2018 06:45
Last Modified: 13 Oct 2023 08:03
DOI: 10.1007/JHEP07(2018)176
Open Access URL: https://link.springer.com/article/10.1007/JHEP07(2...
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URI: https://livrepository.liverpool.ac.uk/id/eprint/3025940