Speaker
Description
In this talk, we present studies of $\tau$ leptons at Belle and the prospects at SuperKEKB/Belle II.
We evaluate the Michel parameters of $\tau$ leptonic decay using Belle’s full data sample. This measurement is important to reveal the Lorentz structure of $\tau$ leptonic decay, which includes not only the $V-A$ interaction but also contributions from scalar, tensor and others that may arise from New Physics; this measurement tests lepton universality as well. We also measure branching fractions of $\tau$ decays into three charged pseudo-scalars and a tau neutrino using the full sample of Belle. In the previous analysis by Belle, some deviation from the existing measurements was seen for the branching fraction on $\tau \to \pi\pi\pi\nu$ mode; we expect to make this clear by our full analysis.
The Belle~II experiment aims to record 50 ab$^{-1}$ of data at the SuperKEKB energy-asymmetric $e^+e^-$ collider. The anticipated high statistics data sample has excellent sensitivity to lepton flavor violating (LFV) $\tau$ lepton decays including $\tau \to \mu \gamma$, $\tau \to \mu \pi^0/\eta$ and so on. Prospects and sensitivities for $\tau$ LFV at Belle~II will be presented.
