The simplest of them all: tt̄W± at NLO accuracy in QCD

Recent measurements of the pp → tt̄W± t t ¯ W ± process in multi-lepton final states, as performed by the ATLAS collaboration in the context of the Higgs boson studies in the tt̄H t t ¯ 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 tt̄W± t t ¯ W ± process. With the goal of understanding and resolving the modelling issues within the SM tt̄W± t t ¯ 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⁺νₑμ⁻ν̄μe⁺νₑbb̄ e + ν e μ − ν ¯ μ e + ν e b b ¯ and e⁻ν̄ₑμ⁺νμe⁻ν̄ₑbb̄ e − ν ¯ e μ + ν μ e − ν ¯ e b b ¯ final state at the LHC with √s s = 13 TeV. 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 tt̄W± t t ¯ W ± cross section is also examined by an explicit comparison to the narrow-width approximation.