Search for lepton-flavor-violating $\tau\to\ell V^0$ decays at Belle

TL;DR

This study searched for lepton-flavor-violating tau decays into a lepton and a vector meson using Belle data, setting new upper limits on their branching fractions due to no observed signal.

Contribution

First search for neutrinoless tau decays into lepton and vector meson modes at Belle, establishing the most restrictive upper limits to date.

Findings

No excess signal observed over background.

Set upper limits on branching fractions between 5.9 and 18 x 10^-8.

First results for tau to lepton omega decay mode.

Abstract

We have searched for neutrinoless $\tau$ lepton decays into $\ell$ and $V^0$, where $\ell$ stands for an electron or muon, and $V^0$ for a vector meson ($\phi$, $\omega$, $K^{*0}$, $\bar{K}^{*0}$ or $\rho^0$), using 543 fb$^{-1}$ of data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No excess of signal events over the expected background has been observed, and we set upper limits on the branching fractions in the range $(5.9-18) \times 10^{-8}$ at the 90% confidence level. These upper limits include the first results for the $\ell \omega$ mode as well as new limits that are significantly more restrictive than our previous results for the $\ell \phi$, $\ell K^{*0}$, $\ell \bar{K}^{*0}$ and $\ell \rho^0$ modes.