Seesaw Model Searches Using Multilepton Final States at the HL-LHC

A simulation-based sensitivity study is performed for physics beyond the standard model (BSM) in the context of neutrino mass mechanisms. The simulated samples correspond to an integrated luminosity of 3000 fb$^{-1}$ of proton-proton collisions at $\sqrt{s} =$ 14 TeV with the Phase-2 CMS detector tuned to the high-luminosity LHC scenario. Type-I and II seesaw models, which can explain the nonzero mass of neutrinos in a most elegant way, are the targeted BSM models. The postulated BSM particles for all 2 models are assumed to be heavy in the study, with masses ranging between 200 and 3000 GeV. The signature used in this search consists of 3 or 4 leptons in any flavor combination of electrons and muons. With a common strategy, the analysis is expected to exclude the mass of BSM fermion singlet $N$ up to 2020 (2440) GeV in the type-I seesaw model for cases where $N$ mixes only with $e (\mu)$ type neutrinos. For the type-II seesaw model, mass of BSM scalar triplet $\Delta$ is excluded up to 1280 (1300) GeV, for normal (inverted) neutrino mass structure.