Distinguishing Dirac/Majorana Sterile Neutrinos at the LHC

TL;DR

This paper proposes a method to distinguish Dirac from Majorana sterile neutrinos at the LHC by comparing decay rates of specific leptonic processes, using collider simulations to assess the feasibility of detection.

Contribution

It introduces a novel approach to identify the nature of sterile neutrinos through decay rate comparisons, applicable at the 14 TeV LHC with high luminosity.

Findings

Discrimination between Dirac and Majorana neutrinos is possible with certain mixing disparities.

At least 3σ exclusion of the Dirac case can be achieved under specified conditions.

The method is effective for sterile neutrino masses of 20 and 50 GeV.

Abstract

We study the purely leptonic decays of $W^\pm \to e^\pm e^\pm \mu^\mp \nu$ and $\mu^\pm \mu^\pm e^\mp \nu$ produced at the LHC, induced by sterile neutrinos with mass $m_N$ below $M_W$ in the intermediate state. Since the final state neutrino escapes detection, one cannot tell whether this process violates lepton number, what would indicate a Majorana character for the intermediate sterile neutrino. Our study shows that when the sterile neutrino mixings with electrons and muons are different enough, one can still discriminate between the Dirac and Majorana character of this intermediate neutrino by simply counting and comparing the above decay rates. After performing collider simulations and statistical analysis, we find that at the $14~\text{TeV}$ LHC with an integrated luminosity of $3000~\text{fb}^{-1}$, for two benchmark scenarios $m_N$ = 20 GeV and 50 GeV, at least a $3\sigma$ level of exclusion on the Dirac case can be achieved for disparities as mild as e.g. $|U_{Ne}|^2 < 0.7~ |U_{N\mu}|^2$ or $|U_{N\mu}|^2 < 0.7~ |U_{N e}|^2$, provided that $|U_{Ne}|^2$, $|U_{N\mu}|^2$ are both above $\sim 2\times 10^{-6}$.