Displaced heavy neutral lepton from new Higgs doublet

Abstract

Heavy neutral leptons N are introduced to explain the tiny neutrino masses via the seesaw mechanism. For proper small mixing parameter \(V_{\ell N},\) the heavy neutral leptons N become long-lived, which leads to the displaced vertex signature at colliders. In this paper, we consider the displaced heavy neutral lepton from the neutrinophilic Higgs doublet \(\Phi _\nu \) decay. The new Higgs doublet with MeV scale VEV can naturally explain the tiny neutrino masses with TeV scale N. Different from current experimental searches via the \(W^\pm \rightarrow \ell ^\pm N\) decay, the branching ratios of new decays as \(H^\pm \rightarrow \ell ^\pm N\) are not suppressed when \(|V_{\ell N}|\gtrsim 10^{-16}.\) Therefore, a larger parameter space is expected to be detected at colliders. We then investigate the promising region at the 14 TeV HL-LHC and the 3 TeV CLIC. According to our simulation, the DV signature could probe \(|V_{\ell N}|^2\gtrsim 10^{-18}\) with \(m_N<m_{H^+},\) which covers the seesaw predicted value \(|V_{\ell N}|^2\sim m_\nu /m_N.\) We could probe \(m_{H^+}\lesssim 1100\) GeV at the 14 TeV HL-LHC and \(m_{H^+}\lesssim 1490\) GeV at the 3 TeV CLIC.