Measurements of the top quark pair production cross section at 7TeV A

Here are presented several measurements of the cross section for the production of top quark pairs in proton-proton collisions at the LHC at a centre-of-mass energy of 7TeV. It has been used data collected with the CMS experiment during the year 2010, and amounting to a total integrated luminosity of 36 pb-1. Measurements are presented in the lepton+jets final state, where events are selected which contain exactly one isolated, highly energetic muon or electron, and at least four jets. In addition, the di-lepton final state, which consists of two leptons, at least two jets, and significant missing transverse energy is explored. Has been used b-jet identification in order to increase the purity of the selection. Important backgrounds are estimated using data-driven techniques, and systematic uncertainties are estimated. The results are compared with theory predictions.