Measurement of the top quark pair production cross section in proton-proton collisions at $\sqrt(s) =$ 13 TeV

The top quark pair production cross section is measured for the first time in proton-proton collisions at s=13 TeV by the CMS experiment at the CERN LHC, using data corresponding to an integrated luminosity of 43 pb-1. The measurement is performed by analyzing events with at least one electron and one muon of opposite charge, and at least two jets. The measured cross section is 746±58(stat)±53(syst)±36(lumi) pb, in agreement with the expectation from the standard model.