Measurement of the τ Michel parameters η and ξκ in the radiative leptonic decay τ- → l- ντνlγ

N. Shimizu; H. Aihara; D. Epifanov; I. Adachi; S. Al Said; D. M. Asner; V. Aulchenko; T. Aushev; R. Ayad; V. Babu; I. Badhrees; A. M. Bakich; V. Bansa; E. Barberio; V. Bhardwaj; B. Bhuyan; J. Biswal; A. Bobrov; A. Bozek; M. Bračko; T. E. Browder; D. Červenkov; M. C. Chang; P. Chang; V. Chekelian; A. Chen; B. G. Cheon; K. Chilikin; K. Cho; S. K. Choi; Y. Choi; D. Cinabro; T. Czank; N. Dash; S. Di Carlo; Z. Doležal; D. Dutta; S. Eidelman; J. E. Fast; T. Ferber; B. G. Fulsom; R. Garg; V. Gaur; N. Gabyshev; A. Garmash; M. Gelb; P. Goldenzweig; D. Greenwald; E. Guido; J. Haba; K. Hayasaka; H. Hayashii; M. T. Hedges; S. Hirose; W. S. Hou; T. Iijima; K. Inami; G. Inguglia; A. Ishikawa; R. Itoh; M. Iwasaki; I. Jaegle; H. B. Jeon; S. Jia; Y. Jin; K. K. Joo; T. Julius; K. H. Kang; G. Karyan; T. Kawasaki; C. Kiesling; D. Y. Kim; J. B. Kim; S. H. Kim; Y. J. Kim; K. Kinoshita; P. Kodyš; S. Korpar; D. Kotchetkov; P. Križan; R. Kroeger; P. Krokovny; R. Kulasiri; A. Kuzmin; Y. J. Kwon; J. S. Lange; I. S. Lee; L. K. Li; Y. Li; L. Li Gioi; J. Libby; D. Liventsev; M. Masuda; M. Merola; K. Miyabayashi; H. Miyata; G. B. Mohanty; H. K. Moon; T. Mori; R. Mussa; E. Nakano; M. Nakao; T. Nanut; K. J. Nath; Z. Natkaniec; M. Nayak; M. Niiyama; N. K. Nisar; S. Nishida; S. Ogawa; S. Okuno; H. Ono; G. Pakhlova; B. Pal; C. W. Park; H. Park; S. Paul; T. K. Pedlar; R. Pestotnik; L. E. Piilonen; V. Popov; M. Ritter; A. Rostomyan; Y. Sakai; M. Salehi; S. Sandilya; Y. Sato; V. Savinov; O. Schneider; G. Schnell; C. Schwanda; Y. Seino; K. Senyo; M. E. Sevior; V. Shebalin; T. A. Shibata; J. G. Shiu; B. Shwartz; A. Sokolov; E. Solovieva; M. Starič; J. F. Strube; K. Sumisawa; T. Sumiyoshi; U. Tamponi; K. Tanida; F. Tenchini; K. Trabelsi; M. Uchida; T. Uglov; Y. Unno; S. Uno; Y. Usov; C. Van Hulse; G. Varner; V. Vorobyev; A. Vossen; C. H. Wang; M. Z. Wang; P. Wang; M. Watanabe; E. Widmann; E. Won; Y. Yamashita; H. Ye; C. Z. Yuan; Z. P. Zhang; V. Zhilich; V. Zhukova; V. Zhulanov; A. Zupanc

doi:10.1093/ptep/pty003

Measurement of the τ Michel parameters η and ξκ in the radiative leptonic decay τ^- → l^- ν_τν_lγ

N. Shimizu, H. Aihara, D. Epifanov, I. Adachi, S. Al Said, D. M. Asner, V. Aulchenko, T. Aushev, R. Ayad, V. Babu, I. Badhrees, A. M. Bakich, V. Bansa, E. Barberio, V. Bhardwaj, B. Bhuyan, J. Biswal, A. Bobrov, A. Bozek, M. BračkoT. E. Browder, D. Červenkov, M. C. Chang, P. Chang, V. Chekelian, A. Chen, B. G. Cheon, K. Chilikin, K. Cho, S. K. Choi, Y. Choi, D. Cinabro, T. Czank, N. Dash, S. Di Carlo, Z. Doležal, D. Dutta, S. Eidelman, J. E. Fast, T. Ferber, B. G. Fulsom, R. Garg, V. Gaur, N. Gabyshev, A. Garmash, M. Gelb, P. Goldenzweig, D. Greenwald, E. Guido, J. Haba, K. Hayasaka, H. Hayashii, M. T. Hedges, S. Hirose, W. S. Hou, T. Iijima, K. Inami, G. Inguglia, A. Ishikawa, R. Itoh, M. Iwasaki, I. Jaegle, H. B. Jeon, S. Jia, Y. Jin, K. K. Joo, T. Julius, K. H. Kang, G. Karyan, T. Kawasaki, C. Kiesling, D. Y. Kim, J. B. Kim, S. H. Kim, Y. J. Kim, K. Kinoshita, P. Kodyš, S. Korpar, D. Kotchetkov, P. Križan, R. Kroeger, P. Krokovny, R. Kulasiri, A. Kuzmin, Y. J. Kwon, J. S. Lange, I. S. Lee, L. K. Li, Y. Li, L. Li Gioi, J. Libby, D. Liventsev, M. Masuda, M. Merola, K. Miyabayashi, H. Miyata, G. B. Mohanty, H. K. Moon, T. Mori, R. Mussa, E. Nakano, M. Nakao, T. Nanut, K. J. Nath, Z. Natkaniec, M. Nayak, M. Niiyama, N. K. Nisar, S. Nishida, S. Ogawa, S. Okuno, H. Ono, G. Pakhlova, B. Pal, C. W. Park, H. Park, S. Paul, T. K. Pedlar, R. Pestotnik, L. E. Piilonen, V. Popov, M. Ritter, A. Rostomyan, Y. Sakai, M. Salehi, S. Sandilya, Y. Sato, V. Savinov, O. Schneider, G. Schnell, C. Schwanda, Y. Seino, K. Senyo, M. E. Sevior, V. Shebalin, T. A. Shibata, J. G. Shiu, B. Shwartz, A. Sokolov, E. Solovieva, M. Starič, J. F. Strube, K. Sumisawa, T. Sumiyoshi, U. Tamponi, K. Tanida, F. Tenchini, K. Trabelsi, M. Uchida, T. Uglov, Y. Unno, S. Uno, Y. Usov, C. Van Hulse, G. Varner, V. Vorobyev, A. Vossen, C. H. Wang, M. Z. Wang, P. Wang, M. Watanabe, E. Widmann, E. Won, Y. Yamashita, H. Ye, C. Z. Yuan, Z. P. Zhang, V. Zhilich, V. Zhukova, V. Zhulanov, A. Zupanc

Department of Physics

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4 Citations (Scopus)

Abstract

We present a measurement of the Michel parameters of the τ lepton, η and ξκ, in the radiative leptonic decay τ^- → l^- ν_τν_lγ using 711 fb^-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^- ν_τν_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.

Original language	English
Journal	Progress of Theoretical and Experimental Physics
Volume	2018
Issue number	2
DOIs	https://doi.org/10.1093/ptep/pty003
Publication status	Published - 2018 Feb 1

ASJC Scopus subject areas

Physics and Astronomy(all)

Access to Document

10.1093/ptep/pty003

Cite this

Shimizu, N., Aihara, H., Epifanov, D., Adachi, I., Said, S. A., Asner, D. M., Aulchenko, V., Aushev, T., Ayad, R., Babu, V., Badhrees, I., Bakich, A. M., Bansa, V., Barberio, E., Bhardwaj, V., Bhuyan, B., Biswal, J., Bobrov, A., Bozek, A., ... Zupanc, A. (2018). Measurement of the τ Michel parameters η and ξκ in the radiative leptonic decay τ^- → l^- ν_τν_lγ. Progress of Theoretical and Experimental Physics, 2018(2). https://doi.org/10.1093/ptep/pty003

Shimizu, N, Aihara, H, Epifanov, D, Adachi, I, Said, SA, Asner, DM, Aulchenko, V, Aushev, T, Ayad, R, Babu, V, Badhrees, I, Bakich, AM, Bansa, V, Barberio, E, Bhardwaj, V, Bhuyan, B, Biswal, J, Bobrov, A, Bozek, A, Bračko, M, Browder, TE, Červenkov, D, Chang, MC, Chang, P, Chekelian, V, Chen, A, Cheon, BG, Chilikin, K, Cho, K, Choi, SK, Choi, Y, Cinabro, D, Czank, T, Dash, N, Di Carlo, S, Doležal, Z, Dutta, D, Eidelman, S, Fast, JE, Ferber, T, Fulsom, BG, Garg, R, Gaur, V, Gabyshev, N, Garmash, A, Gelb, M, Goldenzweig, P, Greenwald, D, Guido, E, Haba, J, Hayasaka, K, Hayashii, H, Hedges, MT, Hirose, S, Hou, WS, Iijima, T, Inami, K, Inguglia, G, Ishikawa, A, Itoh, R, Iwasaki, M, Jaegle, I, Jeon, HB, Jia, S, Jin, Y, Joo, KK, Julius, T, Kang, KH, Karyan, G, Kawasaki, T, Kiesling, C, Kim, DY, Kim, JB, Kim, SH, Kim, YJ, Kinoshita, K, Kodyš, P, Korpar, S, Kotchetkov, D, Križan, P, Kroeger, R, Krokovny, P, Kulasiri, R, Kuzmin, A, Kwon, YJ, Lange, JS, Lee, IS, Li, LK, Li, Y, Gioi, LL, Libby, J, Liventsev, D, Masuda, M, Merola, M, Miyabayashi, K, Miyata, H, Mohanty, GB, Moon, HK, Mori, T, Mussa, R, Nakano, E, Nakao, M, Nanut, T, Nath, KJ, Natkaniec, Z, Nayak, M, Niiyama, M, Nisar, NK, Nishida, S, Ogawa, S, Okuno, S, Ono, H, Pakhlova, G, Pal, B, Park, CW, Park, H, Paul, S, Pedlar, TK, Pestotnik, R, Piilonen, LE, Popov, V, Ritter, M, Rostomyan, A, Sakai, Y, Salehi, M, Sandilya, S, Sato, Y, Savinov, V, Schneider, O, Schnell, G, Schwanda, C, Seino, Y, Senyo, K, Sevior, ME, Shebalin, V, Shibata, TA, Shiu, JG, Shwartz, B, Sokolov, A, Solovieva, E, Starič, M, Strube, JF, Sumisawa, K, Sumiyoshi, T, Tamponi, U, Tanida, K, Tenchini, F, Trabelsi, K, Uchida, M, Uglov, T, Unno, Y, Uno, S, Usov, Y, Van Hulse, C, Varner, G, Vorobyev, V, Vossen, A, Wang, CH, Wang, MZ, Wang, P, Watanabe, M, Widmann, E, Won, E, Yamashita, Y, Ye, H, Yuan, CZ, Zhang, ZP, Zhilich, V, Zhukova, V, Zhulanov, V & Zupanc, A 2018, 'Measurement of the τ Michel parameters η and ξκ in the radiative leptonic decay τ^- → l^- ν_τν_lγ', Progress of Theoretical and Experimental Physics, vol. 2018, no. 2. https://doi.org/10.1093/ptep/pty003

@article{f2f091bc05854203a19329372d2621e0,

title = "Measurement of the τ Michel parameters η and ξκ in the radiative leptonic decay τ- → l- ντνlγ",

abstract = "We present a measurement of the Michel parameters of the τ lepton, η and ξκ, in the radiative leptonic decay τ- → l- ντνlγ using 711 fb-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+π0ντ)(l- ντνlγ)(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.",

author = "N. Shimizu and H. Aihara and D. Epifanov and I. Adachi and Said, {S. Al} and Asner, {D. M.} and V. Aulchenko and T. Aushev and R. Ayad and V. Babu and I. Badhrees and Bakich, {A. M.} and V. Bansa and E. Barberio and V. Bhardwaj and B. Bhuyan and J. Biswal and A. Bobrov and A. Bozek and M. Bra{\v c}ko and Browder, {T. E.} and D. {\v C}ervenkov and Chang, {M. C.} and P. Chang and V. Chekelian and A. Chen and Cheon, {B. G.} and K. Chilikin and K. Cho and Choi, {S. K.} and Y. Choi and D. Cinabro and T. Czank and N. Dash and {Di Carlo}, S. and Z. Dole{\v z}al and D. Dutta and S. Eidelman and Fast, {J. E.} and T. Ferber and Fulsom, {B. G.} and R. Garg and V. Gaur and N. Gabyshev and A. Garmash and M. Gelb and P. Goldenzweig and D. Greenwald and E. Guido and J. Haba and K. Hayasaka and H. Hayashii and Hedges, {M. T.} and S. Hirose and Hou, {W. S.} and T. Iijima and K. Inami and G. Inguglia and A. Ishikawa and R. Itoh and M. Iwasaki and I. Jaegle and Jeon, {H. B.} and S. Jia and Y. Jin and Joo, {K. K.} and T. Julius and Kang, {K. H.} and G. Karyan and T. Kawasaki and C. Kiesling and Kim, {D. Y.} and Kim, {J. B.} and Kim, {S. H.} and Kim, {Y. J.} and K. Kinoshita and P. Kody{\v s} and S. Korpar and D. Kotchetkov and P. Kri{\v z}an and R. Kroeger and P. Krokovny and R. Kulasiri and A. Kuzmin and Kwon, {Y. J.} and Lange, {J. S.} and Lee, {I. S.} and Li, {L. K.} and Y. Li and Gioi, {L. Li} and J. Libby and D. Liventsev and M. Masuda and M. Merola and K. Miyabayashi and H. Miyata and Mohanty, {G. B.} and Moon, {H. K.} and T. Mori and R. Mussa and E. Nakano and M. Nakao and T. Nanut and Nath, {K. J.} and Z. Natkaniec and M. Nayak and M. Niiyama and Nisar, {N. K.} and S. Nishida and S. Ogawa and S. Okuno and H. Ono and G. Pakhlova and B. Pal and Park, {C. W.} and H. Park and S. Paul and Pedlar, {T. K.} and R. Pestotnik and Piilonen, {L. E.} and V. Popov and M. Ritter and A. Rostomyan and Y. Sakai and M. Salehi and S. Sandilya and Y. Sato and V. Savinov and O. Schneider and G. Schnell and C. Schwanda and Y. Seino and K. Senyo and Sevior, {M. E.} and V. Shebalin and Shibata, {T. A.} and Shiu, {J. G.} and B. Shwartz and A. Sokolov and E. Solovieva and M. Stari{\v c} and Strube, {J. F.} and K. Sumisawa and T. Sumiyoshi and U. Tamponi and K. Tanida and F. Tenchini and K. Trabelsi and M. Uchida and T. Uglov and Y. Unno and S. Uno and Y. Usov and {Van Hulse}, C. and G. Varner and V. Vorobyev and A. Vossen and Wang, {C. H.} and Wang, {M. Z.} and P. Wang and M. Watanabe and E. Widmann and E. Won and Y. Yamashita and H. Ye and Yuan, {C. Z.} and Zhang, {Z. P.} and V. Zhilich and V. Zhukova and V. Zhulanov and A. Zupanc",

note = "Funding Information: We would like to express our deepest appreciation to A. Arbuzov, M. Fael, T. Kopylova, L. Mercolli, and M. Passera for very useful discussions and theoretical support of this work. We thank the KEKB group for the excellent operation of the accelerator; the KEK cryogenics group for the efficient operation of the solenoid; and the KEK computer group, the National Institute of Informatics, and the PNNL/EMSL computing group for valuable computing and SINET5 network support. We acknowledge support from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan, the Japan Society for the Promotion of Science (JSPS), and the Tau-Lepton Physics Research Center of Nagoya University; the Australian Research Council; the Austrian Science Fund under Grant No. P 26794-N20; the National Natural Science Foundation of China under Contracts No. 10575109, No. 10775142, No. 10875115, No. 11175187, No. 11475187, No. 11521505, and No. 11575017; the Chinese Academy of Science Center for Excellence in Particle Physics; the Ministry of Education, Youth and Sports of the Czech Republic under Contract No. LTT17020; the Carl Zeiss Foundation, the Deutsche Forschungsgemeinschaft, the Excellence Cluster Universe, and the VolkswagenStiftung; the Department of Science and Technology of India; the Istituto Nazionale di Fisica Nucleare of Italy; the WCU program of the Ministry of Education, National Research Foundation (NRF) of Korea Grants No. 2011-0029457, No. 2012-0008143, No. 2014R1A2A2A01005286, No. 2014R1A2A2A01002734, No. 2015R1A2A2A01003280, No. 2015H1A2A1033649, No. 2016R1D1A1B01010135, No. 2016K1A3A7A09005603, No. 2016K1A3A7 A09005604, No. 2016R1D1A1B02012900, No. 2016K1A3A7A09005606, and No. NRF-2013K1A3A7A0 6056592; the Brain Korea 21-Plus program, Radiation Science Research Institute, Foreign Large-size Research Facility Application Supporting project, and the Global Science Experimental Data Hub Center of the Korea Institute of Science and Technology Information; the Polish Ministry of Science and Higher Education and the National Science Center; the Ministry of Education and Science of the Russian Federation and the Russian Foundation for Basic Research, grant 15-02-05674; the Slovenian Research Agency; Ikerbasque, Basque Foundation for Science and MINECO (Juan de la Cierva), Spain; the Swiss National Science Foundation; the Ministry of Education and the Ministry of Science and Technology of Taiwan; and the U.S. Department of Energy and the National Science Foundation. Publisher Copyright: {\textcopyright} The Author(s) 2018.",

year = "2018",

month = feb,

day = "1",

doi = "10.1093/ptep/pty003",

language = "English",

volume = "2018",

journal = "Progress of Theoretical and Experimental Physics",

issn = "2050-3911",

publisher = "Oxford University Press",

number = "2",

}

TY - JOUR

T1 - Measurement of the τ Michel parameters η and ξκ in the radiative leptonic decay τ- → l- ντνlγ

AU - Shimizu, N.

AU - Aihara, H.

AU - Epifanov, D.

AU - Adachi, I.

AU - Said, S. Al

AU - Asner, D. M.

AU - Aulchenko, V.

AU - Aushev, T.

AU - Ayad, R.

AU - Babu, V.

AU - Badhrees, I.

AU - Bakich, A. M.

AU - Bansa, V.

AU - Barberio, E.

AU - Bhardwaj, V.

AU - Bhuyan, B.

AU - Biswal, J.

AU - Bobrov, A.

AU - Bozek, A.

AU - Bračko, M.

AU - Browder, T. E.

AU - Červenkov, D.

AU - Chang, M. C.

AU - Chang, P.

AU - Chekelian, V.

AU - Chen, A.

AU - Cheon, B. G.

AU - Chilikin, K.

AU - Cho, K.

AU - Choi, S. K.

AU - Choi, Y.

AU - Cinabro, D.

AU - Czank, T.

AU - Dash, N.

AU - Di Carlo, S.

AU - Doležal, Z.

AU - Dutta, D.

AU - Eidelman, S.

AU - Fast, J. E.

AU - Ferber, T.

AU - Fulsom, B. G.

AU - Garg, R.

AU - Gaur, V.

AU - Gabyshev, N.

AU - Garmash, A.

AU - Gelb, M.

AU - Goldenzweig, P.

AU - Greenwald, D.

AU - Guido, E.

AU - Haba, J.

AU - Hayasaka, K.

AU - Hayashii, H.

AU - Hedges, M. T.

AU - Hirose, S.

AU - Hou, W. S.

AU - Iijima, T.

AU - Inami, K.

AU - Inguglia, G.

AU - Ishikawa, A.

AU - Itoh, R.

AU - Iwasaki, M.

AU - Jaegle, I.

AU - Jeon, H. B.

AU - Jia, S.

AU - Jin, Y.

AU - Joo, K. K.

AU - Julius, T.

AU - Kang, K. H.

AU - Karyan, G.

AU - Kawasaki, T.

AU - Kiesling, C.

AU - Kim, D. Y.

AU - Kim, J. B.

AU - Kim, S. H.

AU - Kim, Y. J.

AU - Kinoshita, K.

AU - Kodyš, P.

AU - Korpar, S.

AU - Kotchetkov, D.

AU - Križan, P.

AU - Kroeger, R.

AU - Krokovny, P.

AU - Kulasiri, R.

AU - Kuzmin, A.

AU - Kwon, Y. J.

AU - Lange, J. S.

AU - Lee, I. S.

AU - Li, L. K.

AU - Li, Y.

AU - Gioi, L. Li

AU - Libby, J.

AU - Liventsev, D.

AU - Masuda, M.

AU - Merola, M.

AU - Miyabayashi, K.

AU - Miyata, H.

AU - Mohanty, G. B.

AU - Moon, H. K.

AU - Mori, T.

AU - Mussa, R.

AU - Nakano, E.

AU - Nakao, M.

AU - Nanut, T.

AU - Nath, K. J.

AU - Natkaniec, Z.

AU - Nayak, M.

AU - Niiyama, M.

AU - Nisar, N. K.

AU - Nishida, S.

AU - Ogawa, S.

AU - Okuno, S.

AU - Ono, H.

AU - Pakhlova, G.

AU - Pal, B.

AU - Park, C. W.

AU - Park, H.

AU - Paul, S.

AU - Pedlar, T. K.

AU - Pestotnik, R.

AU - Piilonen, L. E.

AU - Popov, V.

AU - Ritter, M.

AU - Rostomyan, A.

AU - Sakai, Y.

AU - Salehi, M.

AU - Sandilya, S.

AU - Sato, Y.

AU - Savinov, V.

AU - Schneider, O.

AU - Schnell, G.

AU - Schwanda, C.

AU - Seino, Y.

AU - Senyo, K.

AU - Sevior, M. E.

AU - Shebalin, V.

AU - Shibata, T. A.

AU - Shiu, J. G.

AU - Shwartz, B.

AU - Sokolov, A.

AU - Solovieva, E.

AU - Starič, M.

AU - Strube, J. F.

AU - Sumisawa, K.

AU - Sumiyoshi, T.

AU - Tamponi, U.

AU - Tanida, K.

AU - Tenchini, F.

AU - Trabelsi, K.

AU - Uchida, M.

AU - Uglov, T.

AU - Unno, Y.

AU - Uno, S.

AU - Usov, Y.

AU - Van Hulse, C.

AU - Varner, G.

AU - Vorobyev, V.

AU - Vossen, A.

AU - Wang, C. H.

AU - Wang, M. Z.

AU - Wang, P.

AU - Watanabe, M.

AU - Widmann, E.

AU - Won, E.

AU - Yamashita, Y.

AU - Ye, H.

AU - Yuan, C. Z.

AU - Zhang, Z. P.

AU - Zhilich, V.

AU - Zhukova, V.

AU - Zhulanov, V.

AU - Zupanc, A.

N1 - Funding Information: We would like to express our deepest appreciation to A. Arbuzov, M. Fael, T. Kopylova, L. Mercolli, and M. Passera for very useful discussions and theoretical support of this work. We thank the KEKB group for the excellent operation of the accelerator; the KEK cryogenics group for the efficient operation of the solenoid; and the KEK computer group, the National Institute of Informatics, and the PNNL/EMSL computing group for valuable computing and SINET5 network support. We acknowledge support from the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan, the Japan Society for the Promotion of Science (JSPS), and the Tau-Lepton Physics Research Center of Nagoya University; the Australian Research Council; the Austrian Science Fund under Grant No. P 26794-N20; the National Natural Science Foundation of China under Contracts No. 10575109, No. 10775142, No. 10875115, No. 11175187, No. 11475187, No. 11521505, and No. 11575017; the Chinese Academy of Science Center for Excellence in Particle Physics; the Ministry of Education, Youth and Sports of the Czech Republic under Contract No. LTT17020; the Carl Zeiss Foundation, the Deutsche Forschungsgemeinschaft, the Excellence Cluster Universe, and the VolkswagenStiftung; the Department of Science and Technology of India; the Istituto Nazionale di Fisica Nucleare of Italy; the WCU program of the Ministry of Education, National Research Foundation (NRF) of Korea Grants No. 2011-0029457, No. 2012-0008143, No. 2014R1A2A2A01005286, No. 2014R1A2A2A01002734, No. 2015R1A2A2A01003280, No. 2015H1A2A1033649, No. 2016R1D1A1B01010135, No. 2016K1A3A7A09005603, No. 2016K1A3A7 A09005604, No. 2016R1D1A1B02012900, No. 2016K1A3A7A09005606, and No. NRF-2013K1A3A7A0 6056592; the Brain Korea 21-Plus program, Radiation Science Research Institute, Foreign Large-size Research Facility Application Supporting project, and the Global Science Experimental Data Hub Center of the Korea Institute of Science and Technology Information; the Polish Ministry of Science and Higher Education and the National Science Center; the Ministry of Education and Science of the Russian Federation and the Russian Foundation for Basic Research, grant 15-02-05674; the Slovenian Research Agency; Ikerbasque, Basque Foundation for Science and MINECO (Juan de la Cierva), Spain; the Swiss National Science Foundation; the Ministry of Education and the Ministry of Science and Technology of Taiwan; and the U.S. Department of Energy and the National Science Foundation. Publisher Copyright: © The Author(s) 2018.

PY - 2018/2/1

Y1 - 2018/2/1

N2 - We present a measurement of the Michel parameters of the τ lepton, η and ξκ, in the radiative leptonic decay τ- → l- ντνlγ using 711 fb-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+π0ντ)(l- ντνlγ)(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.

AB - We present a measurement of the Michel parameters of the τ lepton, η and ξκ, in the radiative leptonic decay τ- → l- ντνlγ using 711 fb-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+π0ντ)(l- ντνlγ)(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.

UR - http://www.scopus.com/inward/record.url?scp=85062193441&partnerID=8YFLogxK

U2 - 10.1093/ptep/pty003

DO - 10.1093/ptep/pty003

M3 - Article

AN - SCOPUS:85062193441

SN - 2050-3911

VL - 2018

JO - Progress of Theoretical and Experimental Physics

JF - Progress of Theoretical and Experimental Physics

IS - 2

ER -

Measurement of the τ Michel parameters η and ξκ in the radiative leptonic decay τ^- → l^- ν_τν_lγ

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