First measurement of the running of the top quark mass

The first measurement of the running of the top quark mass is presented. The mass of the top quark in the modified minimal subtraction renormalization scheme is extracted from the differential $\mathrm{t\bar{t}}$ cross section as a function of the invariant mass of the $\mathrm{t\bar{t}}$ system via a $\chi^2$ fit to next-to-leading-order differential theory predictions. The differential cross section is measured at the parton level by means of a maximum-likelihood fit to multidifferential distributions of final state observables. The analysis is performed using $\mathrm{t\bar{t}}$ candidate events in the $\mathrm{e}^\pm \mu^\mp$ final state, using data recorded by the CMS experiment at the CERN LHC in 2016 corresponding to an integrated luminosity of $35.9~\mathrm{fb}^{-1}$. The observed running is found to be compatible with the scale dependence predicted by the renormalization group equation.