The simplest of them all: t$(t)over-bar-$W± at NLO accuracy in QCD

Recent measurements of the pp -> t $(t) over bar $W-+/- process in multi-lepton final states, as performed by the ATLAS collaboration in the context of the Higgs boson studies in the t $(t) over bar $H channel, have shown discrepancies between theoretical predictions and experimental data. Such discrepancies have been observed both in the overall normalisation as well as in the modelling of the t $(t) over bar $W-+/- process. With the goal of understanding and resolving the modelling issues within the SM t $(t) over bar $W +/- process we report on the state-of-the-art NLO QCD computation for this process. Specifically, we calculate higher-order corrections to the e(+)nu(e) mu-(nu) over bar (mu)e+nu(e) b (b) over bar and e(-)(nu) over bar (e)+ nu(mu)e(-)(nu) over bar (e)b (b) over bar final state at the LHC with root s = 13TeV. In the computation off-shell top quarks are described by Breit-Wigner propagators, furthermore, double-, single- as well as non-resonant top-quark contributions along with all interference effects are consistently incorporated at the matrix element level. Results at NLO QCD accuracy are presented in the form of fiducial integrated and differential cross sections for two selected renormalisation and factorisation scale choices and three different PDF sets. The impact of the top quark off-shell effects on the t $(t) over bar $W-+/- cross section is also examined by an explicit comparison to the narrow-width approximation.