Top-quark pair production in association with a $W^{\pm }$ gauge boson in the POWHEG-BOX

Abstract

We present a new Monte Carlo event generator for the production of a top-quark pair in association with a $W^{\pm }$ boson at hadron colliders in the POWHEG-BOX framework. We consider the next-to-leading-order QCD corrections to the $pp\to t\bar{t}{W}^{\pm }$ cross section, corresponding to the $\mathcal{O}({\alpha }_s^3\alpha )$ and $\mathcal{O}({\alpha }_s{\alpha }^3)$ 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 fixed-order 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 $\mathcal{O}({\alpha }_s{\alpha }^3)$ 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.

Comments: 52 pages and 36 beautiful plots, matches published version