Unraveling the Scotogenic Model at Muon Collider

Abstract

The Scotogenic model extends the standard model with three singlet fermion $N_i$ and one inert doublet scalar $\eta$ to address the common origin of tiny neutrino mass and dark matter. For fermion dark matter $N_1$, a hierarchical Yukawa structure $|y_{1e}|\ll|y_{1\mu}|\sim|y_{1\tau}|\sim\mathcal{O}(1)$ is usually favored to satisfy constraints from lepton flavor violation and relic density. Such large $\mu$-related Yukawa coupling would greatly enhance the pair production of charged scalar $\eta^\pm$ at the muon collider. In this paper, we investigate the dilepton signature of the Scotogenic model at a 14 TeV muon collider. For the dimuon signature $\mu^+\mu^-+/ \hspace{-0.65em} E_T$, we find that most viable samples can be probed with $200~\text{fb}^{-1}$ data. The ditau signature $\tau^+\tau^-+/ \hspace{-0.65em}E_T$ is usually less promising but is important to probe the small $|y_{1\mu}|$ region. The mono-photon signature $\gamma+/ \hspace{-0.65em} E_T$ could also probe the compressed mass region $M_1\lesssim M_{\eta^\pm}$. Masses of charged scalar $\eta^\pm$ and dark matter $N_1$ can be further extracted by a binned likelihood fit of the dilepton energy.