Novel Signatures of Heavy Neutral Lepton at Muon Collider

Abstract

The Higgs-strahlung process ${\ell }^{+}{\ell }^{-}\to Zh$ is one of the most important production channels of the standard model Higgs boson $h$ at the lepton colliders. The cross section reaches the maximum value slightly above the threshold $\sqrt{s}\sim m_Z+m_h$, and decreases as $\sim 1/s$ at high energies. In the gauged extension models, the new gauge boson $Z^{\prime }$ and heavy Higgs boson $H$ exist after the symmetry breaking. The heavy Higgs-strahlung process ${\ell }^{+}{\ell }^{-}\to Z^{\prime }H$ would also reach the maximum cross section around the threshold $\sqrt{s}\sim m_{Z^{\prime }}+m_H$. Therefore, the future high energy lepton colliders, such as the TeV scale muon collider, are promising to probe this new process. If heavy neutral lepton $N$ is introduced to generate the tiny neutrino masses via seesaw mechanism, novel signatures could arise from ${\mu }^{+}{\mu }^{-}\to Z^{\prime }H\to NN+NN\to 4{\mu }^{\pm }+4J$ and ${\mu }^{+}{\mu }^{-}\to Z^{\prime }H\to {\mu }^{+}{\mu }^{-}+NN\to 3{\mu }^{\pm }+{\mu }^{\mp }+2J$, where the fat-jets $J$ come from the hadronic decay of $W$ bosons. In this paper, we investigate the same-sign tetralepton signature $4{\mu }^{\pm }+4J$ and the same-sign trilepton signature $3{\mu }^{\pm }+{\mu }^{\mp }+2J$ at the 3 TeV and 10 TeV muon collider.

Comments: 24 pages, 8 figures