Top-quark pair production in association with a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>W</mml:mi><mml:mo>±</mml:mo></mml:msup></mml:math> 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 ${W}^{\ifmmode\pm\else\textpm\fi{}}$ boson at hadron colliders in the POWHEG-BOX framework. We consider the next-to-leading-order QCD corrections to the $pp\ensuremath{\rightarrow}t\overline{t}{W}^{\ifmmode\pm\else\textpm\fi{}}$ cross section, corresponding to the $\mathcal{O}({\ensuremath{\alpha}}_{s}^{3}\ensuremath{\alpha})$ and $\mathcal{O}({\ensuremath{\alpha}}_{s}{\ensuremath{\alpha}}^{3})$ 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 modeling of the fiducial volume stemming from missing higher-order corrections, the different parton-shower-matching schemes, and the modeling of decays. We find that the subleading contribution at $\mathcal{O}({\ensuremath{\alpha}}_{s}{\ensuremath{\alpha}}^{3})$ 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.