Search for $H\rightarrow \gamma\gamma$ produced in association with top quarks and constraints on the top quark-Higgs boson Yukawa coupling using data taken at 7 TeV and 8 TeV with the ATLAS detector

A search is performed for Higgs bosons produced in association with top quarks using the diphoton decay mode of the Higgs boson. Selection requirements are optimized separately for leptonic and fully hadronic final states from the top quark decays. The dataset used corresponds to an integrated luminosity of 20.3 $fb^{-1}$ of proton-proton collisions at a center-of-mass energy of 8 TeV and 4.5 $fb^{-1}$ at 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. No significant excess over the background prediction is observed and upper limits are set on the $t\bar{t}H$ production cross section. The observed exclusion upper limit at 95% confidence level is 6.5 times the predicted Standard Model value. In addition, lower and upper limits at 95% confidence level are set on the top quark-Higgs boson Yukawa coupling strength parameter taking into account the changes in the ttH and tH cross sections as well as the $H\rightarrow\gamma\gamma$ branching fraction. A lower limit at 95% confidence level of -1.3 is observed as well as an upper limit of +8.1.