Combined measurement of the ttbar cross section and the b-tagging efficiency in lepton+jets events with CMS

The Large Hadron Collider, build at CERN, is the first collider in the world able to act as a top quark factory. The large amounts of top quark events produced allow us to study the properties of this heavy quark in great detail. We propose a combined measurement of the $t{\bar t}$ cross section and the b-tagging efficiency using the lepton+jets event topology observed by the CMS experiment in the 8 TeV proton collisions of the LHC. The data collected in 2012 used for this measurement corresponds to an integrated luminosity of 2.8 fb$^{-1}$ for muon+jets events and 2.7 fb$^{-1}$ for electron+jets events. The obtained $t\bar t$ cross section is 228.4 $\pm$ 9.0 (stat.) $^{+29.0}_{-26.0}$ (syst.) $\pm$ 10.0 (lumi) pb.