Investigations of the impact of the parton shower tuning in Pythia 8 in the modelling of $\mathrm{t\overline{t}}$ at $\sqrt{s}=8$ and 13 TeV

Studies are presented comparing top quark pair differential distribution data collected with the CMS detector at $\sqrt{s}=8$ and 13 TeV to state-of-the-art theoretical predictions. A tuning of POWHEG v2+PYTHIA8 through jet kinematics in top quark pair events and global variables is described and the studies validating the new settings along with the new event tune are presented. With the new event tune, the description of top quark pair and jet kinematics in top quark pair events, as well as the overall description of observables are improved. Studies of independent matrix element and parton shower scale variations along with initial-state and final-state radiation variations with several differential cross section measurements are also presented and the effects of these variations on particular observables are identified.