Search for top quark decays $t\to qH$, with $H\to \gamma \gamma$, in $\sqrt{s}=13$ TeV $pp$ collisions using the ATLAS detector

Abstract

This article presents a search for flavour-changing neutral currents in the decay of a top quark into an up-type ($q=c,u$) quark and a Higgs boson, where the Higgs boson decays into two photons. The proton--proton collision data set analysed amounts to 36.1 fb${}^{-1}$ at $\sqrt{s}=13$ TeV collected by the ATLAS experiment at the LHC. Top quark pair events are searched for, where one top quark decays into $qH$ and the other decays into $bW$. Both the hadronic and leptonic decay modes of the $W$ boson are used. No significant excess is observed and an upper limit is set on the $t\to cH$ branching ratio of $2.2\times 10^{-3}$ at the 95% confidence level, while the expected limit in the absence of signal is $1.6\times 10^{-3}$. The corresponding limit on the $tcH$ coupling is 0.090 at the 95% confidence level. The observed upper limit on the $t\to uH$ branching ratio is $2.4\times 10^{-3}$.

arXiv comment41 pages in total, author list starting page 25, 7 figures, 3 tables, submitted to JHEP. All figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2016-26/

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