Measurement of the Michel parameters and in the radiative leptonic decay

におけるタウミシェルパラメータ、の測定

清水 信宏*; 谷田 聖   ; Belle Collaboration*; 他169名*

Shimizu, Nobuhiro*; Tanida, Kiyoshi; Belle Collaboration*; 169 of others*

We present a measurement of the Michel parameters of the lepton, and , in the radiative leptonic decay using 711~f of collision data collected with the Belle detector at the KEKB collider. The Michel parameters are measured in an unbinned maximum likelihood fit to the kinematic distribution of or . The measured values of the Michel parameters are and , where the first error is statistical and the second is systematic. This is the first measurement of these parameters. These results are consistent with the Standard Model predictions within their uncertainties and constrain the coupling constants of the generalized weak interaction.