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

Abstract

We study the rare decays of charged π mesons, π+ to e+ e+ μ- anti-ν_μ and π+ to e+ μ- e+ ν_e, induced by a sterile neutrino N with a mass in the range m_μ< m_N < m_π. 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.

20 pages, 8 figures, tex added in the introduction and section 3, equations moved to appendix in section 2