NLO and off-shell effects in top quark mass determinations

We study the impact of different theoretical descriptions of top quark pair production on top quark mass measurements in the di-lepton channel. To this aim, the full NLO corrections to $ pp\to {W}^{+}{W}^{-}b\overline{b}\to \left({e}^{+}{\nu}_e\right)\left({\mu}^{-}{\overline{\nu}}_{\mu}\right)b\overline{b} $ production are compared to calculations in the narrow width approximation, where the production of a top quark pair is calculated at NLO and combined with three different descriptions of the top quark decay: leading order, next-to-leading order and via a parton shower. The different theory predictions then enter the calibration of template fit functions, which are used for a fit to pseudo-data. The offsets in the top quark mass resulting from the fits based on the various theoretical descriptions are determined.