Measurement of the tau Michel parameters $\barη$ and $ξκ$ in the radiative leptonic decay $τ^- \rightarrow \ell^- ν_τ \barν_{\ell}γ$
Creators: name: The Belle Collaboration
name: Shimizu, N.
name: Aihara, H.
name: Epifanov, D.
name: Abdesselam, A.
name: Adachi, I.
name: Adamczyk, K.
name: Said, S. Al
name: Arinstein, K.
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name: Babu, V.
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name: Barberio, E.
name: Barrett, M.
name: Bartel, W.
name: Bay, A.
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name: Belhorn, M.
name: Belous, K.
name: Berger, M.
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name: Besson, D.
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name: Bhuyan, B.
name: Biswal, J.
name: Bloomfield, T.
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name: Bozek, A.
name: Bračko, M.
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name: Breibeck, F.
name: Brodzicka, J.
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name: Waheed, E.
name: Červenkov, D.
name: Chang, M. -C.
name: Chang, P.
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name: Chekelian, V.
name: Chen, A.
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name: Cheon, B. G.
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name: Chistov, R.
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name: Chobanova, V.
name: Choi, S. -K.
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name: Crnkovic, J.
name: Dalseno, J.
name: Danilov, M.
name: Dash, N.
name: Di Carlo, S.
name: Dingfelder, J.
name: Doležal, Z.
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name: Drásal, Z.
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name: Eidelman, S.
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name: Perdekamp, M. Grosse
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name: Grzymkowska, O.
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name: Guo, H.
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name: Han, Y. L.
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name: Heller, A.
name: Higuchi, T.
name: Himori, S.
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name: Horiguchi, T.
name: Hoshi, Y.
name: Hoshina, K.
name: Hou, W. -S.
name: Hsiung, Y. B.
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name: Huschle, M.
name: Hyun, H. J.
name: Igarashi, Y.
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name: Kataoka, S. U.
name: Kato, E.
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name: Kim, J. B.
name: Kim, J. H.
name: Kim, K. T.
name: Kim, M. J.
name: Kim, S. H.
name: Kim, S. K.
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name: Kinoshita, K.
name: Kleinwort, C.
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name: Vahsen, S. E.
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name: Wagner, M. N.
name: Waheed, E.
name: Wang, B.
name: Wang, C. H.
name: Wang, J.
name: Wang, M. -Z.
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name: Wang, X. L.
name: Watanabe, M.
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name: Yusa, Y.
name: Zhang, C. C.
name: Zhang, L. M.
name: Zhang, Z. P.
name: Zhao, L.
name: Zhilich, V.
name: Zhukova, V.
name: Zhulanov, V.
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Publisher: name: arXiv
Year: 2017
Subjects: subject: High Energy Physics - Experiment (hep-ex)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We present a measurement of the Michel parameters of the $τ$ lepton, $\barη$ and $ξκ$, in the radiative leptonic decay $τ^- \rightarrow \ell^- ν_τ \barν_{\ell} γ$ using 711~f$\mathrm{b}^{-1}$ 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 $e^+e^-\rightarrowτ^+τ^-\rightarrow (π^+π^0 \barν_τ)(\ell^-ν_τ\barν_{\ell}γ)$ $(\ell=e$ or $μ)$. The measured values of the Michel parameters are $\barη = -1.3 \pm 1.5 \pm 0.8$ and $ξκ= 0.5 \pm 0.4 \pm 0.2$, 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.