Comparison of ATLAS and CMS nominal $\mathrm{t}\mathrm{\bar t}$ Monte Carlo simulation for Run 2

A preliminary study is performed to compare the Monte Carlo simulation of $\mathrm{t}\mathrm{\bar t}$ events at 13 TeV employed by the ATLAS and CMS experiments. The study focuses on the nominal settings used in each experiment, consisting in interfacing Powheg-box with Pythia8 (v 8.230) using the corresponding ATLAS and CMS experimental tunes. Several variations, including combining ATLAS Powheg settings with CMS Pythia settings and vice versa, have also been tested to gain insight into the sources of differences between the nominal samples used in both experiments. The comparisons are performed at particle-level (no detector simulation involved) using a RIVET analysis plugin.