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

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 -> 2 sub-amplitudes through modified EW interactions. At NLO in QCD, tWZ interferes with t (t) over barZ and t (t) over bar 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 13TeV, including the six relevant dimension-6 operators (O-tW, O-tZ, O-tG, O-phi Q((-)), O-phi Q((3)), O-phi t), also matching short-distance events to parton shower.