Search for top quark decays $t\to qH$ with $H\to \gamma \gamma$ using the ATLAS detector

Abstract

A search is performed for flavour-changing neutral currents in the decay of a top quark to an up-type ($c,u$) quark and a Higgs boson, where the Higgs boson decays to two photons. The proton-proton collision data set used corresponds to 4.7 fb${}^{-1}$ at $\sqrt{s}$ = 7 \tev\ and 20.3 fb${}^{-1}$ at $\sqrt{s}$ = 8 \tev\ collected by the ATLAS experiment at the LHC. Top quark pair events are searched for in which one top quark decays to $qH$ and the other decays to $bW$. Both the hadronic and the leptonic decay modes of the $W$ boson are used. No significant signal is observed and an upper limit is set on the $t\to qH$ branching ratio of 0.79% at the 95% confidence level. The corresponding limit on the $tqH$ coupling combination $\sqrt{{\lambda }_{tcH}^2+{\lambda }_{tuH}^2}$ is 0.17.

22 pages plus author list (45 pages total), 6 figures, 4 tables, submitted to JHEP. All figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HIGG-2013-09

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