Search for flavour-changing neutral currents in processes with one top quark and a photon using 81 fb−1 of pp collisions at √s=13 TeV with the ATLAS experiment
Aad, Georges; Abbott, Brad; Abbott, Dale C.; Abed Abud, Adam; Abeling, Kira; Abhayasinghe, Deshan Kavishka; Abidi, Syed Haider; AbouZeid, Hass; Abraham, Nadine L.; Abramowicz, Halina; Bjørke, Kristian; Bugge, Magnar Kopangen; Cameron, David Gordon; Catmore, James Richard; Garonne, Vincent; Gramstad, Eirik; Hellesund, Simen; Morisbak, Vanja; Oppen, Henrik; Ould-Saada, Farid; Pedersen, Maiken; Read, Alexander Lincoln; Rye, Eli Bæverfjord; Røhne, Ole Myren; Sandaker, Heidi; Vadla, Knut Oddvar Høie; Buanes, Trygve; Djuvsland, Julia Isabell; Eigen, Gerald; Fomin, Nikolai; Lee, Graham Richard; Lipniacka, Anna; Martin dit Latour, Bertrand; Mæland, Steffen; Stugu, Bjarne; Træet, Are Sivertsen; Abreu, Henso; Abulaiti, Yiming; Acharya, Bobby S.; Achkar, Baida; Adachi, Shunsuke; Adam, Lennart; Adam-Bourdarios, Claire; Adamczyk, Leszek; Adamek, Lukas; Adelman, Jareed; Adersberger, Michael; Adigüzel, Aytül; Adorni, Sofia; Adye, Tim; ATLAS, Collaboration
Journal article, Peer reviewed
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Original versionPhysics Letters B. 2020, 800, 135082. 10.1016/j.physletb.2019.135082
A search for flavour-changing neutral current (FCNC) events via the coupling of a top quark, a photon, and an up or charm quark is presented using 81 fb−1 of proton–proton collision data taken at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Events with a photon, an electron or muon, a b-tagged jet, and missing transverse momentum are selected. A neural network based on kinematic variables differentiates between events from signal and background processes. The data are consistent with the background-only hypothesis, and limits are set on the strength of the tqγ coupling in an effective field theory. These are also interpreted as 95% CL upper limits on the cross section for FCNC tγ production via a left-handed (right-handed) tuγ coupling of 36 fb (78 fb) and on the branching ratio for t → γ u of 2.8 × 10−5 (6.1 × 10−5). In addition, they are interpreted as 95% CL upper limits on the cross section for FCNC tγ production via a left-handed (right-handed) tcγ coupling of 40 fb (33 fb) and on the branching ratio for t → γ c of 22 × 10−5 (18 × 10−5).