Constraining the top-Z coupling through t(t)over-barZ production at the LHC

We study top pair production in association with a Z-boson at the LHC, focusing on the sensitivity to the top Z-couplings. As yet, these couplings have not been studied in a hadronic collider environment. We calculate t (t) over barZ production to next-to-leading order in perturbative QCD, and include spin correlations in the top and Z-decays to the same order. We use the cross section measurements made by CMS using 4.9 fb(-1) of data from the root s = 7 TeV LHC run to place constraints on the top-Z couplings through a log-likelihood ratio analysis. Looking ahead to the higher energy run, we use the azimuthal angle between the leptons arising from the Z-decay, which is particularly sensitive to the top-Z coupling, to investigate the constraints that could be obtained using 30, 300, and 3000 fb(-1) of data. We find that using NLO predictions significantly improves the top-Z coupling constraints, due to the decreased scale uncertainty.