Search for neutrinoless decays τ→3ℓ

Abstract

We have searched for neutrinoless τ lepton decays into three charged leptons using an 87.1fb−1 data sample collected with the Belle detector at the KEKB e+e− collider. Since the number of signal candidate events is compatible with that expected from the background, we set 90% confidence level upper limits on the branching fractions in the range (1.9–3.5)×10−7 for various decay modes τ−→ℓ−ℓ+ℓ− where ℓ represents e or μ.