Department

Physics

Document Type

Article

Publication Date

2-2018

Embargo Period

7-3-2018

Abstract

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 within their uncertainties, and constrain the coupling constants of the generalized weak interaction.

Journal

Progress of Theoretical and Experimental Physics

Journal ISSN

2050-3911

Volume

2018

Issue

2

Comments

© The Author(s) 2018. Published by Oxford University Press on behalf of the Physical Society of Japan. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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