Study of the muon decay-in-flight in the τ- →μ- ν ¯ μντ decay to measure the Michel parameter ζ′

D. Bodrov; P. Pakhlov; I. Adachi; H. Aihara; S. Al Said; D. M. Asner; H. Atmacan; T. Aushev; R. Ayad; V. Babu; Sw Banerjee; P. Behera; K. Belous; J. Bennett; M. Bessner; B. Bhuyan; T. Bilka; D. Biswas; A. Bobrov; A. Bondar; J. Borah; A. Bozek; M. Bračko; P. Branchini; T. E. Browder; A. Budano; M. Campajola; D. Červenkov; M. C. Chang; B. G. Cheon; K. Chilikin; K. Cho; S. J. Cho; S. K. Choi; Y. Choi; S. Choudhury; D. Cinabro; S. Das; G. De Nardo; G. De Pietro; R. Dhamija; F. Di Capua; J. Dingfelder; Z. DoleŽal; T. V. Dong; D. Epifanov; T. Ferber; D. Ferlewicz; B. G. Fulsom; V. Gaur; A. Garmash; A. Giri; P. Goldenzweig; E. Graziani; D. Greenwald; T. Gu; Y. Guan; K. Gudkova; C. Hadjivasiliou; S. Halder; K. Hayasaka; H. Hayashii; M. T. Hedges; D. Herrmann; W. S. Hou; C. L. Hsu; T. Iijima; K. Inami; N. Ipsita; A. Ishikawa; R. Itoh; M. Iwasaki; W. W. Jacobs; E. J. Jang; Q. P. Ji; S. Jia; Y. Jin; K. K. Joo; D. Kalita; A. B. Kaliyar; K. H. Kang; T. Kawasaki; C. Kiesling; C. H. Kim; D. Y. Kim; K. H. Kim; Y. K. Kim; H. Kindo; K. Kinoshita; P. Kodyš; A. Korobov; S. Korpar; P. KriŽan; P. Krokovny; T. Kuhr; M. Kumar; R. Kumar; K. Kumara; Y. J. Kwon; J. S. Lange; S. C. Lee; J. Li; L. K. Li; Y. Li; J. Libby; K. Lieret; Y. R. Lin; D. Liventsev; Y. Ma; M. Masuda; T. Matsuda; S. K. Maurya; F. Meier; M. Merola; F. Metzner; K. Miyabayashi; R. Mizuk; G. B. Mohanty; R. Mussa; I. Nakamura; M. Nakao; D. Narwal; Z. Natkaniec; A. Natochii; L. Nayak; M. Nayak; N. K. Nisar; S. Nishida; S. Ogawa; H. Ono; P. Oskin; G. Pakhlova; S. Pardi; H. Park; J. Park; S. H. Park; S. Patra; S. Paul; T. K. Pedlar; R. Pestotnik; L. E. Piilonen; T. Podobnik; E. Prencipe; M. T. Prim; A. Rabusov; G. Russo; S. Sandilya; A. Sangal; L. Santelj; V. Savinov; G. Schnell; C. Schwanda; Y. Seino; K. Senyo; W. Shan; M. Shapkin; C. Sharma; J. G. Shiu; J. B. Singh; A. Sokolov; E. Solovieva; M. Starič; Z. S. Stottler; M. Sumihama; M. Takizawa; U. Tamponi; K. Tanida; F. Tenchini; R. Tiwary; K. Trabelsi; M. Uchida; T. Uglov; Y. Unno; K. Uno; S. Uno; S. E. Vahsen; G. Varner; A. Vinokurova; A. Vossen; D. Wang; E. Wang; M. Z. Wang; S. Watanuki; X. Xu; B. D. Yabsley; W. Yan; S. B. Yang; J. Yelton; J. H. Yin; C. Z. Yuan; Y. Yusa; Z. P. Zhang; V. Zhilich; V. Zhukova

doi:10.1103/PhysRevD.108.012003

Study of the muon decay-in-flight in the τ- →μ- ν ¯ μντ decay to measure the Michel parameter ζ′

D. Bodrov, P. Pakhlov, I. Adachi, H. Aihara, S. Al Said, D. M. Asner, H. Atmacan, T. Aushev, R. Ayad, V. Babu, Sw Banerjee, P. Behera, K. Belous, J. Bennett, M. Bessner, B. Bhuyan, T. Bilka, D. Biswas, A. Bobrov, A. BondarJ. Borah, A. Bozek, M. Bračko, P. Branchini, T. E. Browder, A. Budano, M. Campajola, D. Červenkov, M. C. Chang, B. G. Cheon, K. Chilikin, K. Cho, S. J. Cho, S. K. Choi, Y. Choi, S. Choudhury, D. Cinabro, S. Das, G. De Nardo, G. De Pietro, R. Dhamija, F. Di Capua, J. Dingfelder, Z. DoleŽal, T. V. Dong, D. Epifanov, T. Ferber, D. Ferlewicz, B. G. Fulsom, V. Gaur, A. Garmash, A. Giri, P. Goldenzweig, E. Graziani, D. Greenwald, T. Gu, Y. Guan, K. Gudkova, C. Hadjivasiliou, S. Halder, K. Hayasaka, H. Hayashii, M. T. Hedges, D. Herrmann, W. S. Hou, C. L. Hsu, T. Iijima, K. Inami, N. Ipsita, A. Ishikawa, R. Itoh, M. Iwasaki, W. W. Jacobs, E. J. Jang, Q. P. Ji, S. Jia, Y. Jin, K. K. Joo, D. Kalita, A. B. Kaliyar, K. H. Kang, T. Kawasaki, C. Kiesling, C. H. Kim, D. Y. Kim, K. H. Kim, Y. K. Kim, H. Kindo, K. Kinoshita, P. Kodyš, A. Korobov, S. Korpar, P. KriŽan, P. Krokovny, T. Kuhr, M. Kumar, R. Kumar, K. Kumara, Y. J. Kwon, J. S. Lange, S. C. Lee, J. Li, L. K. Li, Y. Li, J. Libby, K. Lieret, Y. R. Lin, D. Liventsev, Y. Ma, M. Masuda, T. Matsuda, S. K. Maurya, F. Meier, M. Merola, F. Metzner, K. Miyabayashi, R. Mizuk, G. B. Mohanty, R. Mussa, I. Nakamura, M. Nakao, D. Narwal, Z. Natkaniec, A. Natochii, L. Nayak, M. Nayak, N. K. Nisar, S. Nishida, S. Ogawa, H. Ono, P. Oskin, G. Pakhlova, S. Pardi, H. Park, J. Park, S. H. Park, S. Patra, S. Paul, T. K. Pedlar, R. Pestotnik, L. E. Piilonen, T. Podobnik, E. Prencipe, M. T. Prim, A. Rabusov, G. Russo, S. Sandilya, A. Sangal, L. Santelj, V. Savinov, G. Schnell, C. Schwanda, Y. Seino, K. Senyo, W. Shan, M. Shapkin, C. Sharma, J. G. Shiu, J. B. Singh, A. Sokolov, E. Solovieva, M. Starič, Z. S. Stottler, M. Sumihama, M. Takizawa, U. Tamponi, K. Tanida, F. Tenchini, R. Tiwary, K. Trabelsi, M. Uchida, T. Uglov, Y. Unno, K. Uno, S. Uno, S. E. Vahsen, G. Varner, A. Vinokurova, A. Vossen, D. Wang, E. Wang, M. Z. Wang, S. Watanuki, X. Xu, B. D. Yabsley, W. Yan, S. B. Yang, J. Yelton, J. H. Yin, C. Z. Yuan, Y. Yusa, Z. P. Zhang, V. Zhilich, V. Zhukova

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Abstract

We present the first measurement of the Michel parameter ζ′ in the τ-→μ-ν¯μντ decay using the full data sample of 988 fb-1 collected by the Belle detector operating at the KEKB asymmetric energy e+e- collider. The method is based on the reconstruction of the μ-→e-ν¯eνμ decay-in-flight in the Belle central drift chamber and relies on the correlation between muon spin and its daughter electron momentum. We study the main sources of the background that can imitate the signal decay, such as kaon and pion decays-in-flight and charged particle scattering on the detector material. Highly efficient methods of their suppression are developed and applied to select 165 signal-candidate events. We obtain ζ′=0.22±0.94±0.42 where the first uncertainty is statistical, and the second one is systematic. The result is in agreement with the Standard Model prediction of ζ′=1.

Original language	English
Article number	012003
Journal	Physical Review D
Volume	108
Issue number	1
DOIs	https://doi.org/10.1103/PhysRevD.108.012003
State	Published - 1 Jul 2023

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10.1103/PhysRevD.108.012003

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Bodrov, D., Pakhlov, P., Adachi, I., Aihara, H., Al Said, S., Asner, D. M., Atmacan, H., Aushev, T., Ayad, R., Babu, V., Banerjee, S., Behera, P., Belous, K., Bennett, J., Bessner, M., Bhuyan, B., Bilka, T., Biswas, D., Bobrov, A., ... Zhukova, V. (2023). Study of the muon decay-in-flight in the τ- →μ- ν ¯ μντ decay to measure the Michel parameter ζ′. Physical Review D, 108(1), Article 012003. https://doi.org/10.1103/PhysRevD.108.012003

@article{d6c4b72fb3b94a8d9c0270c88c28fc8f,

title = "Study of the muon decay-in-flight in the τ- →μ- ν ¯ μντ decay to measure the Michel parameter ζ′",

abstract = "We present the first measurement of the Michel parameter ζ′ in the τ-→μ-ν¯μντ decay using the full data sample of 988 fb-1 collected by the Belle detector operating at the KEKB asymmetric energy e+e- collider. The method is based on the reconstruction of the μ-→e-ν¯eνμ decay-in-flight in the Belle central drift chamber and relies on the correlation between muon spin and its daughter electron momentum. We study the main sources of the background that can imitate the signal decay, such as kaon and pion decays-in-flight and charged particle scattering on the detector material. Highly efficient methods of their suppression are developed and applied to select 165 signal-candidate events. We obtain ζ′=0.22±0.94±0.42 where the first uncertainty is statistical, and the second one is systematic. The result is in agreement with the Standard Model prediction of ζ′=1.",

author = "D. Bodrov and P. Pakhlov and I. Adachi and H. Aihara and {Al Said}, S. and Asner, {D. M.} and H. Atmacan and T. Aushev and R. Ayad and V. Babu and Sw Banerjee and P. Behera and K. Belous and J. Bennett and M. Bessner and B. Bhuyan and T. Bilka and D. Biswas and A. Bobrov and A. Bondar and J. Borah and A. Bozek and M. Bra{\v c}ko and P. Branchini and Browder, {T. E.} and A. Budano and M. Campajola and D. {\v C}ervenkov and Chang, {M. C.} and Cheon, {B. G.} and K. Chilikin and K. Cho and Cho, {S. J.} and Choi, {S. K.} and Y. Choi and S. Choudhury and D. Cinabro and S. Das and {De Nardo}, G. and {De Pietro}, G. and R. Dhamija and {Di Capua}, F. and J. Dingfelder and Z. Dole{\v Z}al and Dong, {T. V.} and D. Epifanov and T. Ferber and D. Ferlewicz and Fulsom, {B. G.} and V. Gaur and A. Garmash and A. Giri and P. Goldenzweig and E. Graziani and D. Greenwald and T. Gu and Y. Guan and K. Gudkova and C. Hadjivasiliou and S. Halder and K. Hayasaka and H. Hayashii and Hedges, {M. T.} and D. Herrmann and Hou, {W. S.} and Hsu, {C. L.} and T. Iijima and K. Inami and N. Ipsita and A. Ishikawa and R. Itoh and M. Iwasaki and Jacobs, {W. W.} and Jang, {E. J.} and Ji, {Q. P.} and S. Jia and Y. Jin and Joo, {K. K.} and D. Kalita and Kaliyar, {A. B.} and Kang, {K. H.} and T. Kawasaki and C. Kiesling and Kim, {C. H.} and Kim, {D. Y.} and Kim, {K. H.} and Kim, {Y. K.} and H. Kindo and K. Kinoshita and P. Kody{\v s} and A. Korobov and S. Korpar and P. Kri{\v Z}an and P. Krokovny and T. Kuhr and M. Kumar and R. Kumar and K. Kumara and Kwon, {Y. J.} and Lange, {J. S.} and Lee, {S. C.} and J. Li and Li, {L. K.} and Y. Li and J. Libby and K. Lieret and Lin, {Y. R.} and D. Liventsev and Y. Ma and M. Masuda and T. Matsuda and Maurya, {S. K.} and F. Meier and M. Merola and F. Metzner and K. Miyabayashi and R. Mizuk and Mohanty, {G. B.} and R. Mussa and I. Nakamura and M. Nakao and D. Narwal and Z. Natkaniec and A. Natochii and L. Nayak and M. Nayak and Nisar, {N. K.} and S. Nishida and S. Ogawa and H. Ono and P. Oskin and G. Pakhlova and S. Pardi and H. Park and J. Park and Park, {S. H.} and S. Patra and S. Paul and Pedlar, {T. K.} and R. Pestotnik and Piilonen, {L. E.} and T. Podobnik and E. Prencipe and Prim, {M. T.} and A. Rabusov and G. Russo and S. Sandilya and A. Sangal and L. Santelj and V. Savinov and G. Schnell and C. Schwanda and Y. Seino and K. Senyo and W. Shan and M. Shapkin and C. Sharma and Shiu, {J. G.} and Singh, {J. B.} and A. Sokolov and E. Solovieva and M. Stari{\v c} and Stottler, {Z. S.} and M. Sumihama and M. Takizawa and U. Tamponi and K. Tanida and F. Tenchini and R. Tiwary and K. Trabelsi and M. Uchida and T. Uglov and Y. Unno and K. Uno and S. Uno and Vahsen, {S. E.} and G. Varner and A. Vinokurova and A. Vossen and D. Wang and E. Wang and Wang, {M. Z.} and S. Watanuki and X. Xu and Yabsley, {B. D.} and W. Yan and Yang, {S. B.} and J. Yelton and Yin, {J. H.} and Yuan, {C. Z.} and Y. Yusa and Zhang, {Z. P.} and V. Zhilich and V. Zhukova",

note = "Publisher Copyright: {\textcopyright} 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the {"}https://creativecommons.org/licenses/by/4.0/{"}Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.",

year = "2023",

month = jul,

day = "1",

doi = "10.1103/PhysRevD.108.012003",

language = "English",

volume = "108",

journal = "Physical Review D",

issn = "2470-0010",

publisher = "American Physical Society",

number = "1",

}

Bodrov, D, Pakhlov, P, Adachi, I, Aihara, H, Al Said, S, Asner, DM, Atmacan, H, Aushev, T, Ayad, R, Babu, V, Banerjee, S, Behera, P, Belous, K, Bennett, J, Bessner, M, Bhuyan, B, Bilka, T, Biswas, D, Bobrov, A, Bondar, A, Borah, J, Bozek, A, Bračko, M, Branchini, P, Browder, TE, Budano, A, Campajola, M, Červenkov, D, Chang, MC, Cheon, BG, Chilikin, K, Cho, K, Cho, SJ, Choi, SK, Choi, Y, Choudhury, S, Cinabro, D, Das, S, De Nardo, G, De Pietro, G, Dhamija, R, Di Capua, F, Dingfelder, J, DoleŽal, Z, Dong, TV, Epifanov, D, Ferber, T, Ferlewicz, D, Fulsom, BG, Gaur, V, Garmash, A, Giri, A, Goldenzweig, P, Graziani, E, Greenwald, D, Gu, T, Guan, Y, Gudkova, K, Hadjivasiliou, C, Halder, S, Hayasaka, K, Hayashii, H, Hedges, MT, Herrmann, D, Hou, WS, Hsu, CL, Iijima, T, Inami, K, Ipsita, N, Ishikawa, A, Itoh, R, Iwasaki, M, Jacobs, WW, Jang, EJ, Ji, QP, Jia, S, Jin, Y, Joo, KK, Kalita, D, Kaliyar, AB, Kang, KH, Kawasaki, T, Kiesling, C, Kim, CH, Kim, DY, Kim, KH, Kim, YK, Kindo, H, Kinoshita, K, Kodyš, P, Korobov, A, Korpar, S, KriŽan, P, Krokovny, P, Kuhr, T, Kumar, M, Kumar, R, Kumara, K, Kwon, YJ, Lange, JS, Lee, SC, Li, J, Li, LK, Li, Y, Libby, J, Lieret, K, Lin, YR, Liventsev, D, Ma, Y, Masuda, M, Matsuda, T, Maurya, SK, Meier, F, Merola, M, Metzner, F, Miyabayashi, K, Mizuk, R, Mohanty, GB, Mussa, R, Nakamura, I, Nakao, M, Narwal, D, Natkaniec, Z, Natochii, A, Nayak, L, Nayak, M, Nisar, NK, Nishida, S, Ogawa, S, Ono, H, Oskin, P, Pakhlova, G, Pardi, S, Park, H, Park, J, Park, SH, Patra, S, Paul, S, Pedlar, TK, Pestotnik, R, Piilonen, LE, Podobnik, T, Prencipe, E, Prim, MT, Rabusov, A, Russo, G, Sandilya, S, Sangal, A, Santelj, L, Savinov, V, Schnell, G, Schwanda, C, Seino, Y, Senyo, K, Shan, W, Shapkin, M, Sharma, C, Shiu, JG, Singh, JB, Sokolov, A, Solovieva, E, Starič, M, Stottler, ZS, Sumihama, M, Takizawa, M, Tamponi, U, Tanida, K, Tenchini, F, Tiwary, R, Trabelsi, K, Uchida, M, Uglov, T, Unno, Y, Uno, K, Uno, S, Vahsen, SE, Varner, G, Vinokurova, A, Vossen, A, Wang, D, Wang, E, Wang, MZ, Watanuki, S, Xu, X, Yabsley, BD, Yan, W, Yang, SB, Yelton, J, Yin, JH, Yuan, CZ, Yusa, Y, Zhang, ZP, Zhilich, V & Zhukova, V 2023, 'Study of the muon decay-in-flight in the τ- →μ- ν ¯ μντ decay to measure the Michel parameter ζ′', Physical Review D, vol. 108, no. 1, 012003. https://doi.org/10.1103/PhysRevD.108.012003

TY - JOUR

T1 - Study of the muon decay-in-flight in the τ- →μ- ν ¯ μντ decay to measure the Michel parameter ζ′

AU - Bodrov, D.

AU - Pakhlov, P.

AU - Adachi, I.

AU - Aihara, H.

AU - Al Said, S.

AU - Asner, D. M.

AU - Atmacan, H.

AU - Aushev, T.

AU - Ayad, R.

AU - Babu, V.

AU - Banerjee, Sw

AU - Behera, P.

AU - Belous, K.

AU - Bennett, J.

AU - Bessner, M.

AU - Bhuyan, B.

AU - Bilka, T.

AU - Biswas, D.

AU - Bobrov, A.

AU - Bondar, A.

AU - Borah, J.

AU - Bozek, A.

AU - Bračko, M.

AU - Branchini, P.

AU - Browder, T. E.

AU - Budano, A.

AU - Campajola, M.

AU - Červenkov, D.

AU - Chang, M. C.

AU - Cheon, B. G.

AU - Chilikin, K.

AU - Cho, K.

AU - Cho, S. J.

AU - Choi, S. K.

AU - Choi, Y.

AU - Choudhury, S.

AU - Cinabro, D.

AU - Das, S.

AU - De Nardo, G.

AU - De Pietro, G.

AU - Dhamija, R.

AU - Di Capua, F.

AU - Dingfelder, J.

AU - DoleŽal, Z.

AU - Dong, T. V.

AU - Epifanov, D.

AU - Ferber, T.

AU - Ferlewicz, D.

AU - Fulsom, B. G.

AU - Gaur, V.

AU - Garmash, A.

AU - Giri, A.

AU - Goldenzweig, P.

AU - Graziani, E.

AU - Greenwald, D.

AU - Gu, T.

AU - Guan, Y.

AU - Gudkova, K.

AU - Hadjivasiliou, C.

AU - Halder, S.

AU - Hayasaka, K.

AU - Hayashii, H.

AU - Hedges, M. T.

AU - Herrmann, D.

AU - Hou, W. S.

AU - Hsu, C. L.

AU - Iijima, T.

AU - Inami, K.

AU - Ipsita, N.

AU - Ishikawa, A.

AU - Itoh, R.

AU - Iwasaki, M.

AU - Jacobs, W. W.

AU - Jang, E. J.

AU - Ji, Q. P.

AU - Jia, S.

AU - Jin, Y.

AU - Joo, K. K.

AU - Kalita, D.

AU - Kaliyar, A. B.

AU - Kang, K. H.

AU - Kawasaki, T.

AU - Kiesling, C.

AU - Kim, C. H.

AU - Kim, D. Y.

AU - Kim, K. H.

AU - Kim, Y. K.

AU - Kindo, H.

AU - Kinoshita, K.

AU - Kodyš, P.

AU - Korobov, A.

AU - Korpar, S.

AU - KriŽan, P.

AU - Krokovny, P.

AU - Kuhr, T.

AU - Kumar, M.

AU - Kumar, R.

AU - Kumara, K.

AU - Kwon, Y. J.

AU - Lange, J. S.

AU - Lee, S. C.

AU - Li, J.

AU - Li, L. K.

AU - Li, Y.

AU - Libby, J.

AU - Lieret, K.

AU - Lin, Y. R.

AU - Liventsev, D.

AU - Ma, Y.

AU - Masuda, M.

AU - Matsuda, T.

AU - Maurya, S. K.

AU - Meier, F.

AU - Merola, M.

AU - Metzner, F.

AU - Miyabayashi, K.

AU - Mizuk, R.

AU - Mohanty, G. B.

AU - Mussa, R.

AU - Nakamura, I.

AU - Nakao, M.

AU - Narwal, D.

AU - Natkaniec, Z.

AU - Natochii, A.

AU - Nayak, L.

AU - Nayak, M.

AU - Nisar, N. K.

AU - Nishida, S.

AU - Ogawa, S.

AU - Ono, H.

AU - Oskin, P.

AU - Pakhlova, G.

AU - Pardi, S.

AU - Park, H.

AU - Park, J.

AU - Park, S. H.

AU - Patra, S.

AU - Paul, S.

AU - Pedlar, T. K.

AU - Pestotnik, R.

AU - Piilonen, L. E.

AU - Podobnik, T.

AU - Prencipe, E.

AU - Prim, M. T.

AU - Rabusov, A.

AU - Russo, G.

AU - Sandilya, S.

AU - Sangal, A.

AU - Santelj, L.

AU - Savinov, V.

AU - Schnell, G.

AU - Schwanda, C.

AU - Seino, Y.

AU - Senyo, K.

AU - Shan, W.

AU - Shapkin, M.

AU - Sharma, C.

AU - Shiu, J. G.

AU - Singh, J. B.

AU - Sokolov, A.

AU - Solovieva, E.

AU - Starič, M.

AU - Stottler, Z. S.

AU - Sumihama, M.

AU - Takizawa, M.

AU - Tamponi, U.

AU - Tanida, K.

AU - Tenchini, F.

AU - Tiwary, R.

AU - Trabelsi, K.

AU - Uchida, M.

AU - Uglov, T.

AU - Unno, Y.

AU - Uno, K.

AU - Uno, S.

AU - Vahsen, S. E.

AU - Varner, G.

AU - Vinokurova, A.

AU - Vossen, A.

AU - Wang, D.

AU - Wang, E.

AU - Wang, M. Z.

AU - Watanuki, S.

AU - Xu, X.

AU - Yabsley, B. D.

AU - Yan, W.

AU - Yang, S. B.

AU - Yelton, J.

AU - Yin, J. H.

AU - Yuan, C. Z.

AU - Yusa, Y.

AU - Zhang, Z. P.

AU - Zhilich, V.

AU - Zhukova, V.

N1 - Publisher Copyright: © 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.

PY - 2023/7/1

Y1 - 2023/7/1

N2 - We present the first measurement of the Michel parameter ζ′ in the τ-→μ-ν¯μντ decay using the full data sample of 988 fb-1 collected by the Belle detector operating at the KEKB asymmetric energy e+e- collider. The method is based on the reconstruction of the μ-→e-ν¯eνμ decay-in-flight in the Belle central drift chamber and relies on the correlation between muon spin and its daughter electron momentum. We study the main sources of the background that can imitate the signal decay, such as kaon and pion decays-in-flight and charged particle scattering on the detector material. Highly efficient methods of their suppression are developed and applied to select 165 signal-candidate events. We obtain ζ′=0.22±0.94±0.42 where the first uncertainty is statistical, and the second one is systematic. The result is in agreement with the Standard Model prediction of ζ′=1.

AB - We present the first measurement of the Michel parameter ζ′ in the τ-→μ-ν¯μντ decay using the full data sample of 988 fb-1 collected by the Belle detector operating at the KEKB asymmetric energy e+e- collider. The method is based on the reconstruction of the μ-→e-ν¯eνμ decay-in-flight in the Belle central drift chamber and relies on the correlation between muon spin and its daughter electron momentum. We study the main sources of the background that can imitate the signal decay, such as kaon and pion decays-in-flight and charged particle scattering on the detector material. Highly efficient methods of their suppression are developed and applied to select 165 signal-candidate events. We obtain ζ′=0.22±0.94±0.42 where the first uncertainty is statistical, and the second one is systematic. The result is in agreement with the Standard Model prediction of ζ′=1.

UR - http://www.scopus.com/inward/record.url?scp=85164943866&partnerID=8YFLogxK

U2 - 10.1103/PhysRevD.108.012003

DO - 10.1103/PhysRevD.108.012003

M3 - Article

AN - SCOPUS:85164943866

SN - 2470-0010

VL - 108

JO - Physical Review D

JF - Physical Review D

IS - 1

M1 - 012003

ER -

Study of the muon decay-in-flight in the τ- →μ- ν ¯ μντ decay to measure the Michel parameter ζ′

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