Measurement of the tt̄ production cross section in the τ+jets channel in pp collisions at √s = 7 TeV

The top-quark pair production cross section in 7 TeV center-of-mass energy proton–proton collisions is measured using data collected by the CMS detector at the LHC. The measurement uses events with one jet identified as a hadronically decaying τ lepton and at least four additional energetic jets, at least one of which is identified as coming from a b quark. The analyzed data sample corresponds to an integrated luminosity of 3.9 fb^(−1) recorded by a dedicated multijet plus hadronically decaying τ trigger. A neural network has been developed to separate the top-quark pairs from the W+jets and multijet backgrounds. The measured value of σ_(tt)=152±12(stat.)±32(syst.)±3(lum.) pb is consistent with the standard model predictions.