Investigating the leptonic couplings of doubly charged scalars at the muon collider

Abstract

We study the lepton flavour conserving and violating couplings of a doubly charged scalar at a 3 TeV muon collider. Using a model independent Lagrangian, we analyse the electron electron, muon muon, and tau tau final states mediated by the doubly charged scalar to probe individual couplings to mu e, mu mu, and mu tau. We find that for a doubly charged scalar of mass greater than 1 TeV and order one couplings, we achieve high signal significance in these channels. We delineate the collider s sensitivity in the mass vs coupling plane, highlighting the extensive reach of the muon collider in probing these couplings far beyond the current experimental limits. We also propose an angular distribution variable to discriminate the exchange of a doubly charged scalar from that of a neutral scalar, which give identical signals.

Figures (15)

• Figure 1: The $t$-channel Feynman diagram correspond to the $H^{\pm\pm}$ mediated signal process $\mu^{+} \mu^{-} \to \ell^{+}_{i} \ell^{-}_{j}$, where the index stands for $i, j = e, \mu, \tau$.
• Figure 2: The allowed region in the $m_{H^{\pm\pm}}~vs.~h_{\mu i}$ (where $i = \mu, e, \tau$) plane after simultaneously satisfying all relevant flavor data shown in Table \ref{['Tab:flavour']}. The blue shaded region represents the allowed region of the parameter space after imposing available flavor bounds.
• Figure 3: Variation of cross-section at the 3 TeV muon collider corresponding to $t$-channel $H^{\pm\pm}$ exchange diagram (Fig. \ref{['Fig:feynman']}) as a function of $m_{H^\pm\pm}$. We have set $h_{\mu i} =1$, and the index $i$ in $\left|h_{\mu i}\right|$ represents $i = e, \mu, \tau$, respectively. The horizontal lines correspond to cross-sections of various SM background processes.
• Figure 4: Normalized distribution of kinetic variables $E^{\text{Miss}}_{T}$(left panel) and $p_T (\ell_1)$ (right panel) for both the signal and SM backgrounds for $\mu^+\mu^-$ final state.
• Figure 5: Normalized distribution of kinetic variables $E^{\text{Miss}}_{T}$(left panel) and $p_T (\ell_1)$ (right panel) for both the signal and SM backgrounds for $e^+e^-$ final state.