Abstract: The first measurement of vector-boson production associated with a top quark-antiquark pair in protonproton collisions at ffiffi s p ¼ 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 ttZ events and a same-sign dilepton analysis of ttV (V ¼ W or Z) events. In the trilepton channel a direct measurement of the ttZ cross section ttZ ¼ 0:28þ0:14 0:11 ðstatÞ þ0:06 0:03 ðsystÞ pb is obtained. In the dilepton channel a measurement of the ttV cross section yields ttV ¼ 0:43þ0:17 0:15 ðstatÞ þ0:09 0:07 ðsystÞ 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 0:137þ0:012 0:016 and 0:306þ0:031 0:053 pb.

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