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

Please always quote using this URN: urn:nbn:de:bvb:20-opus-172568

• 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 significantThis 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 $${t → cH}$$ branching ratio of 2.2 × 10$$^{−3}$$ at the 95% confidence level, while the expected limit in the absence of signal is 1.6 × 10$$^{−3}$$. The corresponding limit on the $$tcH$$ coupling is 0.090 at the 95% confidence level. The observed upper limit on the $${t → uH}$$ branching ratio is 2.4 × 10$$^{−3}$$.