Long-lived heavy neutrino searches at the colliders

A $𝑈(1)_𝑋$ extension of the Standard Model is a simple and consistent framework to naturally incorporate three Right-Handed Neutrinos for generating the observed light neutrino masses and mixing by the seesaw mechanism.We examine the collider testability of the $𝑈(1)_𝑋$ model,both in its minimal form with the conventional charges,as well as with an alternative charge assignment,via the resonant production of the 𝑍'-boson and its subsequent decay into a pair of RHNs.We first derive an updated upper limit on the new gauge coupling $𝑔_𝑋$ as a function of the $M_{𝑍^′}$ from the latest LHC dilepton searches.Then we identify the maximum possible cross section for the RHN pair-production under these constraints.We investigate the possibility of having one of the RHNs long-lived,even for a TeV-scale mass.Employing the general parametrization for the light neutrino mass matrix to reproduce the observed neutrino data,we perform a parameter scan to find the allowed region for the long-lived RHNs.