Same-Sign Tetralepton Signature in Type-II Seesaw at Lepton Colliders

Abstract

The same-sign tetralepton signature via mixing of neutral Higgs bosons and their cascade decays to charged Higgs bosons is a unique signal in the type-II seesaw model. In this paper, we study this signature at future lepton colliders, such as ILC, CLIC, and MuC. Constrained by direct search, $H^{\pm \pm }\to W^{\pm }{W}^{\pm }$ is the only viable decay mode for $M_{A^0}=400$ GeV at $\sqrt{s}=1$ TeV ILC. With an integrated luminosity of $\mathcal{L}=8{\mathrm{ab}}^{-1}$, the promising region with about 150 signal events corresponds to a narrow band in the range of $10^{-4}\text{GeV}\lesssim v_{\Delta }\lesssim 10^{-2}$ GeV. For heavier triplet scalars $M_{A^0}\gtrsim 900$ GeV, although the $H^{\pm \pm }\to {\ell }^{\pm }{\ell }^{\pm }$ decay mode is allowed, the cascade decays are suppressed. A maximum event number $\sim 16$ can be obtained around $v_{\Delta }\sim 4\times 10^{-4}$ GeV and ${\lambda }_4\sim 0.26$ for $M_{A^0}=1000$ GeV with $\mathcal{L}=5{\mathrm{ab}}^{-1}$ at $\sqrt{s}=3$ TeV CLIC. Meanwhile, we find that this signature is not promising for $M_{A^0}=1500$ GeV at $\sqrt{s}=6$ TeV MuC.

Comments: 12 pages, 5 figures