Search for Flavor-Changing Neutral Currents in Top Quark Decays t → Hc and t → Hu in Multilepton Final States in Proton-Proton Collisions at √s =13 TeV with the ATLAS Detector
Abhayasinghe, D. K.
Abidi, S. H.
Izen, Joseph M.
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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(t→Hc) < 0.16% and ℬ(t→Hu) < 0.19% at 95% confidence level are obtained (with expected limits of 0.15% in both cases). © 2018 CERN.