Modeling uncertainties of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>t</mml:mi><mml:mover accent="true"><mml:mi>t</mml:mi><mml:mo stretchy="false">¯</mml:mo></mml:mover><mml:msup><mml:mi>W</mml:mi><mml:mo>±</mml:mo></mml:msup></mml:math> multilepton signatures
Giuseppe Bevilacqua, Huan-Yu Bi, F. Febres Cordero, Heribertus Bayu Hartanto, Manfred Kraus, Jasmina Nasufi, Laura Reina, Małgorzata Worek
Abstract
In light of recent discrepancies between the modeling of $t\overline{t}{W}^{\ifmmode\pm\else\textpm\fi{}}$ 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 $t\overline{t}{W}^{\ifmmode\pm\else\textpm\fi{}}$ 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 $\sqrt{s}=13\text{ }\text{ }\mathrm{TeV}$ for which we study separately the multilepton signatures as predicted from the dominant next-to-leading-order (NLO) contributions at the perturbative orders $\mathcal{O}({\ensuremath{\alpha}}_{s}^{3}{\ensuremath{\alpha}}^{6})$ and $\mathcal{O}({\ensuremath{\alpha}}_{s}{\ensuremath{\alpha}}^{8})$. 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 $pp\ensuremath{\rightarrow}t\overline{t}{W}^{\ifmmode\pm\else\textpm\fi{}}$ matched to parton showers.