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

Abstract

We have searched for neutrinoless $τ$ lepton decays into $\ell$ and $V^0$, where $\ell$ stands for an electron or muon, and $V^0$ for a vector meson ($ϕ$, $ω$, $K^{*0}$, $\bar{K}^{*0}$ or $ρ^0$), 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 $\ell ω$ mode as well as new limits that are significantly more restrictive than our previous results for the $\ell ϕ$, $\ell K^{*0}$, $\ell \bar{K}^{*0}$ and $\ell ρ^0$ modes.

7 pages, 16 figures