Charged Higgs bosons in naturally aligned two-Higgs-doublet models at the LHC

Abstract

Measurements of a Higgs boson at the Large Hadron Collider (LHC) have become increasingly consistent with the predictions of the Standard Model (SM). This fact puts severe constraints on many potential low-energy extensions of the Higgs sector of the SM. In the well-known two-Higgs-doublet model (2HDM), an ``alignment limit'' of parameters readily furnishes one SM-like scalar and can be achieved naturally through an underlying symmetry. Among the other physical states of the 2HDM, a charged scalar ${H}^{\ifmmode\pm\else\textpm\fi{}}$ would provide striking evidence of new physics if observed. We propose a novel technique for the observation of the process $pp\ensuremath{\rightarrow}tb{H}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}t\overline{t}b\overline{b}$ in the dileptonic decay channel at the LHC. The reconstruction of events in this channel is complicated by multiple $b$ jets and unobserved neutrinos in the final state. To determine the neutrino momenta, we implement a neutrino weighting procedure to study, for the first time, the $t\overline{t}b\overline{b}$ signature. We further train a pair of boosted decision trees to reconstruct and classify signal events. We determine the resulting reach within the context of naturally aligned 2HDMs, such as the maximally symmetric two-Higgs-doublet model (MS2HDM). By testing at the integrated luminosity of $150\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ achieved in run 2 of the LHC, we find that this channel may restrict the parameter space of a type-II MS2HDM with charged Higgs masses as high as 680 GeV.