Reconstructing a Heavy Neutral Lepton at the LHC

TL;DR

This paper demonstrates that the mass of a heavy neutral lepton can be reconstructed at the LHC despite missing neutrino momentum, potentially improving bounds on its mixing with standard neutrinos.

Contribution

The study introduces a method to reconstruct heavy neutral lepton mass at the LHC, enhancing search strategies beyond current approaches.

Findings

Mass of heavy neutral lepton can be reconstructed at the LHC.

Mass peak search could improve bounds on mixing parameter.

Method applicable for any mass above the W boson mass.

Abstract

Heavy lepton singlets $N$ slightly mixed with a standard neutrino $\nu_\ell$ are usually searched for at the LHC in the trilepton plus $p_{\rm T}^{\rm miss}$ channel: $pp \to W^+ \to \ell^+ N$ with $N\to \ell^- W^+ \to \ell^- \ell'^+ \nu$. We show that, although the longitudinal momentum of the final $\nu$ 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 $m_N\ge M_W$.