First experimental investigation of the running of the top quark mass

The first measurement of the running of the top quark mass is presented. The running is extracted from a measurement of the differential top quark-antiquark pair production cross section as a function of the invariant mass of the ttbar system. The differential cross section is determined at the parton level by means of a maximum-likelihood fit to distributions of final-state observables using ttbar candidate events in the emu final state. Finally, the running is extracted at next-to-leading order by comparing fixed-order theory predictions to the measured cross section.