Parton shower effects in $t\bar{t}{W}^{\pm }$ production at NLO QCD

We present a selection of results from our recent study of $pp\to t\bar{t}W^\pm$ production matched to partons showers at NLO QCD at the LHC. Theoretical predictions are obtained at perturbative orders $\mathcal{O}({\alpha }_s^3\alpha )$ and $\mathcal{O}({\alpha }_s{\alpha }^3)$, where the different contributions are studied first separately at the inclusive level before being combined within a realistic two same-sign lepton signature. We investigate in detail uncertainties originating from missing higher-order corrections and from the parton-shower matching scheme employed.