ATLAS collaboration (2891 authors)Aguilar-Saavedra, Juan AntonioAmor Dos Santos, Susana PatriciaAnjos, NunoAraque, Juan PedroCantrill, RobertCarvalho, JoãoCastro, Nuno FilipeConde Muiño, PatriciaDa Cunha Sargedas De Sousa, Mario JoseDo Valle Wemans, AndréFiolhais, MiguelGalhardo, BrunoGomes, AgostinhoGonçalo, RicardoJorge, PedroLopes, LourencoMachado Miguens, JoanaMaio, AméliaManeira, JoséMarques, CarlosOnofre, AntónioPalma, AlbertoPedro, RutePina, João AntonioPinto, BelmiroSantos, HelenaSaraiva, JoãoSilva, JoséTavares Delgado, AdemarVeloso, FilipeWolters, Helmut2019-02-042019-02-042014http://dx.doi.org/10.1007/JHEP06(2014)008http://hdl.handle.net/10400.26/26554A 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 $t\rightarrow qH$ 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.engjournal article2019-02-04