Single top production in association with a $WZ$ pair at the LHC in the SMEFT

Abstract: We study single top quark production in association with a $WZ$ pair at the LHC in the context of the Standard Model (SM) and the Standard Model Effective Field Theory (SMEFT). A significant advantage of $tWZ$ compared to other EW top production processes is its sensitivity to unitarity-violating behaviour induced in its $2\to2$ sub-amplitudes through modified EW interactions. At NLO in QCD, $tWZ$ interferes with $t\bar{t}Z$ and $t\bar{t}$ and a method to meaningfully separate it from these overlapping processes needs to be employed. In order to define $tWZ$ production for total rates and differential distributions, we consider the approaches proposed in the literature for similar cases and find that diagram-removal procedures provide reliable results both for the SM and the SMEFT in a suitably defined phase-space region. We provide robust results for total and differential cross sections for $tWZ$ at 13 TeV, including the six relevant dimension-6 operators ($\mathcal{O}{tW}$,$\mathcal{O}{tZ}$,$\mathcal{O}{tG}$,$\mathcal{O}{\phi Q}^{(-)}$,$\mathcal{O}_{\phi Q}^{(3)}$,$\mathcal{O}_{\phi t}$), also matching short-distance events to parton shower.