Determination of the systematic uncertainty due to the Monte Carlo modelling for the measurement of the inclusive t anti tγ cross section with ATLAS

Since the observation of the top quark, many of its properties have been measured but often with large uncertainties. The electroweak couplings of the top quark are one example of these properties. These couplings can be investigated by probing top quark pair events in association with a gauge boson, such as t anti tγ or t anti tZ. In the t anti tγ analyses, the calculations used to produce the signal sample are performed at leading order. More precise analyses would profit from using a next-to-leading order sample. Although the calculations for top quark production with an additional photon at next-to-leading order exist, an event generator is not available yet. In absence of a NLO t anti tγ sample, it is reasonable and needed to consider a systematic uncertainty, which should cover the uncertainty of LO event generation. In this presentation, the determination of the systematic uncertainty due to the Monte Carlo modelling for the measurement of the inclusive t anti tγ cross section with ATLAS is presented.