Top-quark pair production in association with a \nW±\n gauge boson in the POWHEG-BOX

Abstract

Abstract We present a new Monte Carlo event generator for the production of a top-quark pair in association with a W± boson at hadron colliders in the POWHEG-BOX framework. We consider the next-to-leading-order QCD corrections to the pp → tt̄W± cross section, corresponding to the O(α3 sα) and O(αsα) terms in the perturbative expansion of the parton-level cross section, and model the decays of W and top quarks at leading order retaining spin correlations. The fixedorder QCD calculation is further interfaced with the PYTHIA8 parton-shower event generator via the POWHEG method as implemented in the POWHEG-BOX. The corresponding code is now part of the public repository of the POWHEG-BOX. We perform a comparison of different event generators for both the case of inclusive production and the case of the two same-sign leptons signature at the Large Hadron Collider operating at a center-of-mass energy of 13 TeV. We investigate theoretical uncertainties in the modelling of the fiducial volume stemming from missing higher-order corrections, the different parton shower matching schemes, and the modelling of decays. We find that the subleading contribution at O(αsα) is particularly sensitive to differences in the matching scheme and higher-order parton shower effects. We observe that in particular jet observables can differ quite visibly although these differences play only a subordinate role in the description of physical observables once all contributions are combined.