Search for flavor-changing neutral currents in $t\rightarrow cH$, with $H\to\gamma\gamma$, and limit on the tcH coupling

A search for flavour changing neutral currents in top quark decays $t\rightarrow cH$, with $H\to\gamma\gamma$ at $m_{H} = 126.8$ GeV, using 20 fb$^{-1}$ of $\sqrt{s}$ = 8 TeV and 5 fb$^{-1}$ of $\sqrt{s}$ = 7 TeV data collected by the ATLAS experiment at the LHC, is reported. The analysis is based on $t\bar{t}$ events in which one top decays to $cH$, the other decays to $bW$, and both the hadronic and the leptonic decay modes of the $W$ are used and combined. No significant signal is observed and an upper limit on the branching ratio of 0.83% (0.53% expected) at the 95% confidence level is set. The corresponding limit on the $tcH$ coupling is 0.17 (0.14 expected).