Probing a scalar singlet-triplet extension of the Standard Model via VBF at the Muon Collider

TL;DR

This paper explores the potential of a future muon collider to detect scalar triplet and singlet extensions of the Standard Model, focusing on their signatures and constraints from current data.

Contribution

It introduces a novel analysis of scalar triplet and singlet particles at a muon collider, including decay channels, collider signatures, and sensitivity projections at 3 TeV and 10 TeV energies.

Findings

3 TeV MuC can probe triplet scalars up to 450 GeV.

10 TeV MuC can detect triplet scalars up to 800 GeV.

BDT classifier improves detection sensitivity at lower energies.

Abstract

In this article, we investigate the $Y=0$ $SU(2)$ scalar triplet and $Z_2$-odd scalar singlet extension of the Standard Model (SM). Here, the triplet charged Higgs boson decays to $ZW^\pm$, breaking the custodial symmetry at the tree-level, proportional to the triplet vev, while the singlet provides the dark matter (DM) relic. The triplet neutral Higgs ($T^0$) can decay fully invisibly owing to the triplet-singlet portal coupling $\lambda_{st}$. The other SM Higgs portal couplings $\lambda_{ht}, \lambda_{hs}$ are constrained by the Higgs to di-photon 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^\pm, T^0 $) via vector boson fusion with Forward muon tagging, at the centre-of-mass energies of 3 TeV and 10 TeV. The analysis is comprised of a traditional cut-based approach and a 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 $\lambda_{st}$, 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 $T^\pm \to ZW^\pm \to 3$-lepton decay up to 800 GeV of triplet scalar mass from cut-based analysis, with $\lambda_{st}$ as low as 1.5 being adequate.