Measurement of the of $\tau^- \rightarrow \pi^- \nu_{\tau} e^+ e^-$ branching fraction by Belle

Preliminary result of the measurement of the branching fraction of rare tau decay, $\tau^- \rightarrow \pi^- \nu_{\tau} e^+ e^-$, is presented. A 562 $\rm fb^{-1}$ data set collected with Belle detector at the KEKB asymmetric-energy $\rm e^+ e^-$ collider is used. The branching fraction of $\tau^- \rightarrow \pi^- e^+ e^- \nu_\tau$ is measured to be $\mathcal{B}(\tau^ \rightarrow \pi^- e^+ e^- \nu_\tau) = (2.11 \pm 0.19 \pm 0.30) \times 10^{-5}$, where the first uncertainty is statistical and the second is systematic. The measured result is consistent with the theoretical prediction from the Standard Model and could facilitate searches for physics beyond the Standard Model.