Speaker
Kiyoshi Hayasaka
Description
We evaluate the Michel parameters of τ decays using the full data sample of Belle. This is important to reveal the Lorentz structure of τ leptonic decays, which includes not only the V - A interaction but also contributions from scalar, tensor and others that may arise from New Physics, thus testing lepton universality as well. We use both tau+ → l+ nu nu and tau+ → l+ gamma nu nu. We also measure branching fractions of τ decays into three charged leptons and two neutrinos as well as charged pion, lepton-pairs and a neutrino. Recently, their precise theoretical prediction of the branching fractions are given (O(10^-5 .. -7)) and the statistics of the Belle data allows us to achieve the first observation for them.
