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

TL;DR

This study searches for lepton flavor violating tau decays into a lepton and a vector meson using Belle data, setting new upper limits on their branching fractions and improving previous constraints.

Contribution

First search for $ au o ext{lepton} + V^0$ decays with Belle data, providing the most restrictive upper limits to date for these processes.

Findings

No signal observed for lepton flavor violating decays.

Set upper limits on branching fractions between (0.7 - 1.8) x 10^{-7}.

First results for $ au o ext{lepton} + ext{omega}$ decays.

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 ($\phi$, $\omega$, $K^{*0}$ or $\bar{K}^{*0}$), 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 is observed, and we set upper limits on the branching fractions in the range $(0.7 - 1.8) \times 10^{-7}$ at the 90% confidence level. These upper limits include the first results for $\ell \omega$ as well as new limits that are $3.6 - 9.6$ times more restrictive than our previous results for $\ell \phi$, $\ell K^{*0}$ and $\ell \bar{K}^{*0}$.