Top quark pair cross-section measurement using CMS data at a 7 TeV centre-of-mass energy

We present several measurements of the top quark pair production in data collected by the CMS detector at the LHC at a centre-of-mass energy of 7 TeV. We use data collected during the years 2010 and 2011. We give an overview of the top pair cross-section measurement analyses at CMS, presenting all the exploited channels. We use dilepton, lepton + jets and fully hadronic topologies. In the dilepton channel we look for a final state containing two electrons or muons and high missing transverse energy and at least two jets. In the lepton + jets and hadronic channels one or two W bosons originating from the top quark is allowed to decay hadronically; we therefore require repectively at least 4 or 6 jets. b-jet identification is used in order to enhance signal purity in the final selection. We also present advanced analysis techniques such as data-driven background estimation. The results of the measurements, including systematic uncertainties, are presented and discussed. They are then compared with the theoretical predictions and with the current results of the CDF and D0 collaborations at the Tevatron, and an outlook of expected progress of the CMS experiment is given.