Observation of top-quark pair production in association with a photon and measurement of the $t\bar{t}\gamma$ production cross section in pp collisions at $\sqrt{s}=7$ TeV using the ATLAS detector

ATLAS Collaboration

A search is performed for top-quark pairs ($t\bar{t}$) produced together with a photon ($\gamma$) with transverse energy greater than 20 GeV using a sample of $t\bar{t}$ candidate event…