Second China LHC Physics Workshop (CLHCP 2016): 第2届中国LHC物理工作会议

A search for the production of a single top quark in association with a Z boson is presented, both to identify the expected standard model (SM) process and to search for flavour changing neutral current (FCNC) interactions. The data sample corresponds to an integrated luminosity of √19.7 fb−1 recorded by the CMS experiment at the LHC in proton-proton collisions at s = 8 TeV. Final states with three leptons, electrons or muons and at least one jet are investigated. A moderate excess of events compatible with SM tZq production is observed, and the corresponding cross section is measured to be σ ( pp → tZq → νb + − q ) = 10^+8.2_− 7.0 fb with a significance of 2.4 standard deviations. No presence of FCNC production of tZ(q) is observed. Exclusion limits at 95% confidence level on the branching fractions of a top quark decaying to a Z boson and an up or a charm quark are found to be Br(t→Zu)<0.022% and Br(t →Zc)<0.049%, respectively.