Cross section measurement of $t\bar{t}\gamma$ production in $pp$ collision at $\sqrt{s} = 8 \text{TeV}$ with the ATLAS experiment

The cross-section of top-quark pair production in association with a photon in proton-proton collisions at a center of mass energy of $\sqrt{s} = 8~\text{TeV}$ is measured. The data with a total integrated luminosity of $20.2~\text{fb}^{-1}$ collected by the ATLAS detector in 2012 is used. The measurement is performed in the single lepton decay channel. The signal region is defined by the final state of exactly one high $p_{\text{T}}$ lepton, large missing transverse momentum, at least four jets where at least one is being $b$-tagged and exactly one photon with $p_{\text{T}} > 15~\text{GeV}$. The cross-section times the branching ratio is determined in a fiducial region defined in terms of the detector acceptance. The measured $t\bar{t}\gamma$ fiducial cross-section is in good agreement with the NLO prediction. In addition, the differential cross section as a function of photon $p_{\text{T}}$ and $\eta$ is measured.