Search for top quark decays t → qH with H → γγ using the ATLAS detector

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} $ = 7TeV and 20.3fb −1 at $ \sqrt{s} $ = 8TeV 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 → 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.