Lepton Number Violation at Colliders from Kinematically Inaccessible Gauge Bosons

Abstract

We reevaluate the necessity of $W_R$ gauge bosons being kinematically accessible to test the Left-Right Symmetric Model (LRSM) at hadron colliders. In the limit that $W_R$ are too heavy, resonant production of sub-TeV Majorana neutrinos $N$ can still proceed at the Large Hadron Collider (LHC) via the process $pp\to W_R^{\pm \ast }\to N{\ell }^{\pm }\to {\ell }^{\pm }{\ell }^{\pm }+nj$ if mediated by a far off-shell $W_R$. Traditional searches strategies are insensitive to this regime as they rely on momenta of final states scaling with TeV-scale $M_{W_R}$. For such situations, the process is actually kinematically and topologically identical to the direct production (DP) process $pp\to W_{\mathrm{SM}}^{\pm \ast }\to N{\ell }^{\pm }\to {\ell }^{\pm }{\ell }^{\pm }+nj$. In this context, we reinterpret $\sqrt{s}=8$ TeV LHC constraints on DP rates for the minimal LRSM. For $m_N=200-500$ GeV and right-left coupling ratio ${\kappa }_R=g_R/g_L$, we find $(M_{W_R}/{\kappa }_R)>1.1-1.8$ TeV at 95\% CLs. Expected sensitivities to DP at 14 (100) TeV are also recast: with $\mathcal{L}=1(10){\text{ab}}^{-1}$, one can probe $(M_{W_R}/{\kappa }_R)<7.9-8.9(14-40)$ TeV for $m_N=100-700(1200)$ GeV. Findings in terms of gauge invariant dimension-six operators with heavy $N$ are also reported.

Comments: Published version. Minor typos, additional references. Results unchanged