In this article, we investigate the Y=0 SU(2) scalar triplet and Z2-odd scalar singlet extension of the standard model (SM). Here, the triplet charged Higgs boson decays to ZW±, breaking the custodial symmetry at the tree level, proportional to the triplet vacuum expectation value, while the singlet provides the dark matter (DM) relic. The triplet neutral Higgs boson (T0) can decay fully invisibly owing to the triplet-singlet portal coupling λst. The other SM Higgs portal couplings λht,λhs are constrained by the Higgs boson to diphoton observations, and the dark matter relic and direct searches as well as invisible Higgs decay bounds, respectively. For a cleaner signature, we indulge in a futuristic multi-TeV muon collider (MuC) to probe both the triplet scalars (T±,T0) via vector boson fusion with forward muon tagging, at the center-of-mass energies of 3 and 10 TeV. The analysis is comprised of a traditional cut-based approach and a boosted decision tree (BDT) classifier, where the latter is more effective for lower energies. With large missing energy contributions to the final states from combinations of DM mass and λst, the 3 TeV MuC is projected to probe triplet scalar masses of 450 GeV with the BDT classifier. The 10 TeV MuC can pinpoint the custodial symmetry breaking T±→ZW±→3-lepton decay up to 800 GeV of triplet scalar mass from cut-based analysis, with λst as low as 1.5 being adequate.
Published by the American Physical Society
2024