Search for flavor-changing neutral currents in top quark decays t -> Hc and t -> Hu in multilepton final states in proton-proton collisions at root s=13 TeV with the ATLAS detector

2018 CERN. Flavor-changing neutral currents are not present in the Standard Model at tree level and are suppressed in loop processes by the unitarity of the Cabibbo-Kobayashi-Maskawa matrix; the corresponding rates for top quark decay processes are experimentally unobservable. Extensions of the Standard Model can generate new flavor-changing neutral current processes, leading to signals which, if observed, would be unambiguous evidence of new interactions. A data set corresponding to an integrated luminosity of 36.1 fb-1 of pp collisions at a center-of-mass energy of s=13 TeV recorded with the ATLAS detector at the Large Hadron Collider is used to search for top quarks decaying to up or charm quarks with the emission of a Higgs boson, with subsequent Higgs boson decay to final states with at least one electron or muon. No signal is observed and limits on the branching fractions B(tHc)<0.16% and B(tHu)<0.19% at 95% confidence level are obtained (with expected limits of 0.15% in both cases).

Aaboud, M., Aad, G., Abbott, B., Abdinov, O., Abeloos, B., Abhayasinghe, D. K., ... Zwalinski, L.

Aaboud, M||Aad, G||Abbott, B||Abdinov, O||Abeloos, B||Abhayasinghe, DK||Abidi, SH||Abouzeid, OS||Abraham, NL||Abramowicz, H||Abreu, H||Abulaiti, Y||Acharya, BS||Adachi, S||Adamczyk, L||Adelman, J||Adersberger, M||Adiguzel, A||Adye, T||Affolder, AA||Afik, Y||Agheorghiesei, C||Aguilar-Saavedra, JA||Ahmadov, F||Aielli, G||Akatsuka, S||Åkesson, TPA||Akilli, E||Akimov, AV||Alberghi, GL||Albert, J||Albicocco, P||Alconada Verzini, MJ||Alderweireldt, S||Aleksa, M||Aleksandrov, IN||Alexa, C||Alexopoulos, T||Alhroob, M||Ali, B||Aliev, M||Alimonti, G||Alison, J||Alkire, SP||Allaire, C||Allbrooke, BMM||Allen, BW||Allport, PP||Aloisio, A||Alonso, A||Alonso, F||Alpigiani, C||Alshehri, AA||Alstaty, MI||Alvarez Gonzalez, B||Álvarez Piqueras, D||Alviggi, MG||Amadio, BT||Amaral Coutinho, Y||Ambroz, L||Amelung, C||Amidei, D||Amor Dos Santos, SP||Amoroso, S||Amrouche, CS||Anastopoulos, C||Ancu, LS||Andari, N||Andeen, T||Anders, CF||Anders, JK||Anderson, KJ||Andreazza, A||Andrei, V||Anelli, CR||Angelidakis, S||Angelozzi, I||Ang

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