Measurement of associated production of vector bosons and top quark-antiquark pairs in pp collisions at √s = 7 TeV

Abstract

The first measurement of vector-boson production associated with a top quark-antiquark pair in proton-proton collisions at √s=7  TeV is presented. The results are based on a data set corresponding to an integrated luminosity of 5.0  fb^(-1), recorded by the CMS detector at the LHC in 2011. The measurement is performed in two independent channels through a trilepton analysis of tt Z events and a same-sign dilepton analysis of tt̅ V (V=W or Z) events. In the trilepton channel a direct measurement of the tt Z cross section σ_(ttZ)=0.28_(-0.11)^(+0.14) (stat)_(-0.03)^(+0.06) (syst)  pb is obtained. In the dilepton channel a measurement of the tt̅ V cross section yields σ_(ttV) =0.43_(-0.15)^(+0.17) (stat)_(-0.07)^(+0.09) (syst)  pb. These measurements have a significance, respectively, of 3.3 and 3.0 standard deviations from the background hypotheses and are compatible, within uncertainties, with the corresponding next-to-leading order predictions of 0.137_(-0.016)^(+0.012) and 0.306_(-0.053)^(+0.031)  pb.

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