In light of recent discrepancies between the modeling of ttW signatures and measurements reported by the Large Hadron Collider (LHC) experimental collaborations, we investigate in detail theoretical uncertainties for multi-lepton signatures. We compare results from the state-of-the-art full off-shell calculation and its Narrow Width Approximation to results obtained from the on-shell ttW calculation, with approximate spin-correlations in top-quark and W decays, matched to parton showers. In the former case double-, single-, and non-resonant contributions together with interference effects are taken into account, while the latter two cases are only based on the double resonant top-quark contributions. The comparison is performed for the LHC at √s=13 TeV for which we study separately the multi-lepton signatures as predicted from the dominant NLO contributions at the perturbative orders O(α3sα6) and O(αsα8). Furthermore, we combine both contributions and propose a simple way to approximately incorporate the full off-shell effects in the NLO computation of on-shell pp→ttW matched to parton showers.
On the modeling uncertainties of ttW± multi-lepton signatures
G. Bevilacqua et al.