Leptonic CP asymmetry and heavy neutrino searches in seesaw scenario

Abstract

We investigate the prospects for probing heavy Majorana neutrinos in the type-I seesaw framework at the 14 TeV LHC. In this scenario, the light-heavy neutrino mixing enables the production of heavy neutrinos in association with charged leptons, followed by decays into dilepton plus dijet final states. We perform a detector-level cut-based analysis of both same-sign (SS) and opposite-sign (OS) dilepton channels and investigate the sensitivity as a function of the ratio $R_{ll}$ of SS to OS events. We derive projected constraints on the light-heavy neutrino mixing as a function of the heavy-neutrino mass. For $R_{ll} \simeq 1$, the sensitivity at $140~\rm{fb}^{-1}$ improves upon current LHC bounds by about one order of magnitude for $M_N \simeq 60-80~\rm{GeV}$, with a further order of magnitude improvement expected at the HL-LHC with $3~\rm{ab}^{-1}$. The sensitivity decreases substantially for smaller $R_{ll}$. We show that, for $50~\text{GeV} \lesssim M_N \lesssim 100~\text{GeV}$, the collider reach is strongly correlated with $R_{ll}$ and the associated CP asymmetry, providing additional motivation for future measurements of $R_{ll}$ and heavy-neutrino oscillations at colliders.