We present results for the production of a $Z$ boson in association with single top at next-to-leading order (NLO), including the decay of the top quark and the $Z$ boson. This electroweak process gives rise to the trilepton signature $l^{+}{l}^{-}{l}^{\prime \pm }+\mathrm{\text{jets}}+\mathrm{\text{missing energy}}$. We present results for this signature and show that the rate is competitive with the contribution of the mixed strong and electroweak production process, $t\overline{t}Z$. As such it should be observable in the full data sample from LHC running at $\sqrt{s}=8\mathrm{TeV}$. The single $\mathrm{\text{top}}+Z$ process is a hitherto unconsidered irreducible background in searches for flavor changing neutral current decays of the top quark in $t\overline{t}$ production. For a selection of cuts used at the LHC involving a $b$-tag it is the dominant background. In the Appendices we also briefly discuss the impact of NLO corrections on the related $tH$ process.

• Received 10 April 2013

DOI:https://doi.org/10.1103/PhysRevD.87.114006