Exploring CP-Violating heavy neutrino oscillations in rare tau decays at Belle II

Understand

In this work, we study the lepton number violating tau decays via two intermediate on-shell Majorana neutrinos $N_j$ into two charged pions, and a charged lepton $\tau^{\pm} \to \pi^{\pm} N_j \to \pi^{\pm} \pi^{\pm} \ell^{\mp}$.

• We consider the scenario where the heavy neutrino masses are within $0.5$ GeV $\leq M_N \leq 1.5$ GeV.
• We evaluated the possibility to measure the modulation of the decay width along the detector length for these processes at taus factories, such as Belle II.
• We study some realistic conditions which could lead to the observation of this phenomenon at futures $\tau$'s factories.