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

We propose new searches that exploit the unique signatures of decaying sterile neutrinos with masses below Mₖ 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^-4--10^-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₍15 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.