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

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 $\ell \bar{K}^{*0}$.