Neutral Scalar Signatures at a Muon Collider in the $Z_3$ symmetric Three Higgs Doublet Model

Abstract

Extending the scalar sector of the Standard Model is a well-motivated approach to exploring physics beyond the Standard Model. In this work, we investigate the phenomenology of the Three Higgs Doublet Model at a future muon collider. The scalar spectrum of the 3HDM comprises three CP-even Higgs bosons, two CP-odd Higgs bosons, and a pair of charged Higgs states. Focusing on Higgs pair production via muon-antimuon annihilation, we study the production and decay of neutral scalar states through the process $μ^+μ^- \to φ_i φ_j$, assuming a mass hierarchy in which the SM-like CP-even Higgs is the lightest state. We analyze several benchmark scenarios leading to $b\bar{b}b\bar{b}$ and $b\bar{b}t\bar{t}$ final states, and perform a cut-and-count analysis at a center-of-mass energy of $\sqrt{s}=3$ TeV. Our results demonstrate that a future muon collider provides a sensitive and promising environment to probe extended Higgs sectors, with neutral scalar states in the mass range of $200-400$ GeV being discoverable with $5σ$ significance for integrated luminosities of $\mathcal{O}(1-4 \ \mathrm{ab}^{-1})$.

Figures (10)

• Figure 1: Allowed parameter space for the mixing angles $\gamma_1$ and $\alpha_3$. The color coding of the plots is the same as that in Figure \ref{['fig:mH2-al1-masses']}.
• Figure 2: Allowed parameter space for the regular mass hierarchy scenario, for the neutral scalars, where the lightest CP-even scalar is identified with the 125 GeV SM-like Higgs boson. The figure presents the allowed regions for the masses of all heavy neutral Higgs states and their correlations with the relevant scalar mixing angles. The blue shaded regions satisfy the theoretical constraints from vacuum stability, perturbativity, and unitarity. The red regions additionally comply with direct search limits, goodness-of-fit requirements, and the flavor constraint from $b \rightarrow s \gamma$. Furthermore, the parameter points also consistent with electroweak precision observables are shown in green.
• Figure 3: Feynman diagram illustrating the scalar boson pair production through $\mu^+\mu^-$ annihilation.
• Figure 4: Scatter plot showing the pair production cross section of $H_2A_2$ on the x-axis, and $H_3A_3$ on the y-axis for benchmark points consistent with all theoretical and experimental bounds.
• Figure 5: Branching Ratio plots of heavy Higgs