In light of recent discrepancies between the modeling of $t\overline{t}{W}^{\pm }$ signatures and measurements reported by the LHC experimental collaborations, we investigate in detail theoretical uncertainties for multilepton 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 $t\overline{t}{W}^{\pm }$ calculation, with approximate spin correlations in top-quark and $W$ decays, matched to parton showers. In the former case double-, single-, and nonresonant 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 $\sqrt{s}=13\mathrm{TeV}$ for which we study separately the multilepton signatures as predicted from the dominant next-to-leading-order (NLO) contributions at the perturbative orders $\mathcal{O}({\alpha }_s^3{\alpha }^6)$ and $\mathcal{O}({\alpha }_s{\alpha }^8)$. 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 $pp\to t\overline{t}{W}^{\pm }$ matched to parton showers.

• Received 20 October 2021
• Accepted 3 January 2022

DOI:https://doi.org/10.1103/PhysRevD.105.014018

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Published by the American Physical Society