Multilepton and lepton jet probes of sub-weak-scale right-handed neutrinos

Abstract

We propose new searches that exploit the unique signatures of decaying sterile neutrinos with masses below ${M}_{W}$ at the LHC, where they can be produced in rare decays of Standard Model gauge bosons. We show that, for few-GeV-scale sterile neutrinos, the LHC experiments can probe mixing angles at the level of ${10}^{\ensuremath{-}4}--{10}^{\ensuremath{-}3}$ through powerful searches that look for a prompt lepton in association with a displaced lepton jet. For higher-mass sterile neutrinos, i.e., ${M}_{N}\ensuremath{\gtrsim}15\text{ }\text{ }\mathrm{GeV}$, run II can explore similarly small mixing angles in prompt multilepton final states. This represents an improvement of up to 2 orders of magnitude in sensitivity to the sterile neutrino production rate.