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Measurement Of The Τ Michel Parameters Η¯ And Ξκ In The Radiative Leptonic Decay Τ−→ℓ−Ντν¯ℓγ, N. Shimizu Et Al., Ratnappuli L. Kulasiri

Faculty and Research Publications

We present a measurement of the Michel parameters of the τ lepton, η¯ and ξκ , in the radiative leptonic decay τ−→ℓ−ντν¯ℓγ using 711 f b−1 of collision data collected with the Belle detector at the KEKB e+e− collider. The Michel parameters are measured in an unbinned maximum likelihood fit to the kinematic distribution of e+e−→τ+τ−→(π+π0ν¯τ)(ℓ−ντν¯ℓγ) (ℓ=e or μ) . The measured values of the Michel parameters are η¯=−1.3±1.5±0.8 and ξκ=0.5±0.4±0.2 , 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 …