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

## TL;DR

This paper investigates the potential to observe CP-violating heavy neutrino oscillations in rare tau decays at Belle II, focusing on lepton number violation and decay width modulation within a specific neutrino mass range.

## Contribution

It introduces a detailed analysis of heavy neutrino oscillations and their CP violation effects in tau decays at Belle II, considering realistic experimental conditions.

## Key findings

- Decay width modulation could be measurable at Belle II.
- Heavy neutrino oscillations may reveal CP violation.
- Feasibility depends on neutrino mass and detector sensitivity.

## Abstract

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.