Reconstructing a Heavy Neutral Lepton at the LHC

Abstract

Heavy lepton singlets $N$ slightly mixed with a standard neutrino $\hat{I}{½}_{\ell }$ are usually searched for at the LHC in the trilepton plus $p_{\mathrm{T}}^{\mathrm{miss}}$ channel: $pp\to W^{+}\to {\ell }^{+}N$ with $N\to {\ell }^{-}{W}^{+}\to {\ell }^{-}{\ell }^{\prime +}\hat{I}½$. We show that, although the longitudinal momentum of the final $\hat{I}½$ escapes detection, the mass of the heavy lepton can be reconstructed. While this possibility has not been considered in recent LHC searches, we find that the search for a mass peak could systematically improve the current collider bounds on the mixing $|V_{\ell N}{|}^2$ for any mass $m_N\ge M_W$.

12 pages, version to appear in JHEP