Production of charged Higgs bosons associated with CP-even Higgs bosons at future multi--TeV muon colliders

Abstract

We report the first results for charged Higgs boson production associated with CP-even Higgses at future multi--TeV muon colliders within the scenario of the Type-Y Two-Higgs-Doublet Model (THDM). The valid parameter regions in the Type-Y THDM are first updated, and based on the allowed parameter space, all two-body decay channels of the charged Higgs boson are then computed with the help of {\tt H-COUP}. Both production processes $\mu^- \mu^+ \to H^\pm H^\mp h, H^\pm H^\mp H \to t\bar{t} b\bar{b} h, t\bar{t} b\bar{b}H$ are scanned over the constrained parameter space of the considered model. The production cross sections can reach $\sim 0.5$ fb in several regions of the parameter space. The results provide an opportunity to probe charged Higgs bosons produced in association with the heavy CP-even Higgses at the high integrated luminosities proposed for future multi--TeV muon colliders. Furthermore, we evaluate the signal significances for $\mu^- \mu^+ \to H^\pm H^\mp h \to t\bar{t} b\bar{b} h \to t\bar{t} b\bar{b} b\bar{b}$ with respect to the Standard Model backgrounds. We also estimate the significances by including the top quark decay into leptons and bottom quarks and considering $b$-tagging. Thanks to the high integrated luminosities anticipated at future multi--TeV muon colliders,we find that the signal significances can exceed $\sim 3\sigma$ at several benchmark points selected in the viable parameter space of the Type-Y THDM.