Probing Majorana neutrinos in rare pi+ to e+ e+ mu- nu decays

TL;DR

This paper investigates rare charged pion decays mediated by sterile neutrinos to identify signatures of Majorana neutrinos and proposes experimental methods to distinguish their nature, with potential observability at future high-luminosity experiments.

Contribution

It introduces a novel approach to differentiate Majorana from Dirac sterile neutrinos using pion decay spectra and assesses experimental prospects for detection.

Findings

Branching ratios could be detectable at future high-luminosity experiments.

Muon spectrum analysis can distinguish Majorana from Dirac neutrinos.

Rare pion decays provide a promising avenue to probe sterile neutrino properties.

Abstract

We study the rare decays of charged \pi\ mesons, \pi+ to e+ e+ \mu- anti-\nu_\mu\ and \pi+ to e+ \mu- e+ \nu_e, induced by a sterile neutrino N with a mass in the range m_\mu < m_N < m_\pi. The first process violates Lepton Number by two units and so occurs only if N is Majorana, while the second process conserves Lepton Number and occurs irrespective of the Majorana or Dirac character of N. We study a way to distinguish the Majorana vs. Dirac character of N in these processes using the muon spectrum. We also find that the branching ratios could be at the reach of high luminosity experiments like Project X at FNAL or any proposed neutrino (or muon) factories worldwide.