Discovering intermediate mass sterile neutrinos through $\tau^- \to \pi^- \mu^- e^+ \nu$ (or $\bar{\nu}$) decay

TL;DR

This paper proposes a method to determine whether intermediate mass sterile neutrinos are Dirac or Majorana particles by analyzing the energy spectra in specific tau decays, focusing on a particular mass range to avoid background noise.

Contribution

It introduces a novel approach using energy spectrum analysis of tau decay products to distinguish neutrino nature, emphasizing a specific mass window for optimal detection.

Findings

Energy spectra can differentiate Dirac and Majorana neutrinos.

Optimal mass range for sterile neutrino detection identified.

No significant background interference in the proposed method.

Abstract

Distinguishing the Dirac and Majorana nature of neutrinos remains one of the most important tasks in neutrino physics. By assuming that the $\tau^- \to \pi^- \mu^- e^+ \nu$ (or $\bar{\nu}$) decay is resonantly enhanced by the exchange of an intermediate mass sterile neutrino $N$, we show that the energy spectrum of emitted pions and muons can be used to easily distinguish between the Dirac and Majorana nature of $N$. This method takes advantage of the fact that the flavor of light neutrinos is not identified in the tau decay under consideration. We find that it is particularly advantageous, because of no competing background events, to search for $N$ in the mass range $m_e + m_{\mu} \leqslant m_N \leqslant m_{\mu} + m_{\pi}$, where $m_X$ denotes the mass of particle $X \in \{ e, \mu, \pi, N \}$.