Novel signatures of heavy neutral lepton at muon collider

A bstract The Higgs-strahlung process ℓ + ℓ − → 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 $$ \sqrt{s}\sim {m}_Z+{m}_h $$ s ~ m Z + m h , and decreases as ∼ 1/ s at high energies. In the gauged extension models, the new gauge boson Z ′ and heavy Higgs boson H exist after the symmetry breaking. The heavy Higgs-strahlung process ℓ + ℓ − → Z ′ H would also reach the maximum cross section around the threshold $$ \sqrt{s}\sim {m}_{Z^{\prime }}+{m}_H $$ s ~ m Z ′ + 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 μ + μ − → Z ′ H → NN + NN → 4 μ ± +4 J and μ + μ − → Z ′ H → μ + μ − + NN → μ ± + μ ∓ + 2 J , where the fat-jets J come from the hadronic decay of W bosons. In this paper, we investigate the same-sign tetralepton signature 4 μ ± + 4 J and the same-sign trilepton signature 3 μ ± + μ ∓ + 2 J at the 3 TeV and 10 TeV muon collider.