We study the pion decays with intermediate on-shell neutrinos N into two electrons and a muon, π±→ → e ±→N → e±→e ±→μ∓ν. We investigate the branching ratios Br±→= [Γ(π- → e-e-μ+ν) ±→ Γ(π+ → e+e+μ-ν)] /Γ(π- → all) and the CP asymmetry ratio for such decays, in the scenario with two different on-shell neutrinos. If N is Dirac, only the lepton number conserving (LC) decays contribute (LC: ν = νeor); if N is Majorana, both LC and lepton number violating (LV) decays contribute (LV: or ν = νμ). The results show that the CP asymmetry is in general very small, but increases and becomes ∼1 when the masses of the two intermediate neutrinos get closer to each other, i.e., when their mass difference becomes comparable with their decay width, . The observation of CP violation in pion decays would be consistent with the existence of the well-motivated νMSM model with two almost degenerate heavy neutrinos. © 2014 IOP Publishing Ltd.
|Journal||Journal of Physics G: Nuclear and Particle Physics|
|Publication status||Published - 1 Jan 2014|