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. 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

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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.

Original languageEnglish
JournalProgress of Theoretical and Experimental Physics
Issue number2
Publication statusPublished - 2018 Feb 1

Bibliographical 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:
© The Author(s) 2018.

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy(all)


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