Search for flavour-changing neutral current top-quark decays t → qZ in proton-proton collisions at √s=13 TeV with the ATLAS detector
Aaboud, Morad; Aad, Georges; Abbott, Brad; Abdinov, Ovsat Bahram oglu; Abeloos, Baptiste; Abidi, Syed Haider; AbouZeid, Hass; Abraham, Nadine L.; Abramowicz, Halina; Abreu, Henso; Buanes, Trygve; Dale, Ørjan; Eigen, Gerald; Fomin, Nikolai; Lipniacka, Anna; Martin dit Latour, Bertrand; Mæland, Steffen; Stugu, Bjarne; Yang, Zongchang; Zalieckas, Justas; Bugge, Magnar Kopangen; Cameron, David Gordon; Catmore, James Richard; Feigl, Simon; Franconi, Laura; Garonne, Vincent; Gjelsten, Børge Kile; Gramstad, Eirik; Morisbak, Vanja; Oppen, Henrik; Ould-Saada, Farid; Read, Alexander Lincoln; Røhne, Ole Myren; Sandaker, Heidi; Serfon, Cédric; Stapnes, Steinar; Vadla, Knut Oddvar Høie; Abulaiti, Yiming; Acharya, Bobby S.; Adachi, Shunsuke; Adamczyk, Leszek; Adelman, Jareed; Adersberger, Michael; Adye, Tim; Affolder, Anthony Allen; Afik, Yoav; Agheorghiesei, Catalin; Aguilar Saavedra, Juan Antonio; Ahmadov, Faig; Aielli, Giulio; ATLAS, Collaboration
Peer reviewed, Journal article
Published version
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Permanent lenke
https://hdl.handle.net/1956/19113Utgivelsesdato
2018-07-31Metadata
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Originalversjon
https://doi.org/10.1007/jhep07(2018)176Sammendrag
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.