First measurement of the Michel parameter $ξ^\prime$ in the $τ^-\toμ^-\barν_μν_τ$ decay at Belle
Creators: name: Belle Collaboration
name: Bodrov, D.
name: Pakhlov, P.
name: Adachi, I.
name: Aihara, H.
name: Said, S. Al
name: Asner, D. M.
name: Atmacan, H.
name: Aushev, T.
name: Ayad, R.
name: Babu, V.
name: Banerjee, Sw.
name: Behera, P.
name: Belous, K.
name: Bennett, J.
name: Bessner, M.
name: Bhuyan, B.
name: Bilka, T.
name: Biswas, D.
name: Bobrov, A.
name: Bondar, A.
name: Borah, J.
name: Bozek, A.
name: Bračko, M.
name: Branchini, P.
name: Browder, T. E.
name: Budano, A.
name: Campajola, M.
name: Červenkov, D.
name: Chang, M. -C.
name: Cheon, B. G.
name: Chilikin, K.
name: Cho, H. E.
name: Cho, K.
name: Cho, S. -J.
name: Choi, S. -K.
name: Choi, Y.
name: Choudhury, S.
name: Cinabro, D.
name: Das, S.
name: De Nardo, G.
name: De Pietro, G.
name: Dhamija, R.
name: Di Capua, F.
name: Dingfelder, J.
name: Doležal, Z.
name: Dong, T. V.
name: Epifanov, D.
name: Ferber, T.
name: Ferlewicz, D.
name: Fulsom, B. G.
name: Gaur, V.
name: Garmash, A.
name: Giri, A.
name: Goldenzweig, P.
name: Graziani, E.
name: Greenwald, D.
name: Gu, T.
name: Guan, Y.
name: Gudkova, K.
name: Hadjivasiliou, C.
name: Halder, S.
name: Hayasaka, K.
name: Hayashii, H.
name: Hedges, M. T.
name: Herrmann, D.
name: Hou, W. -S.
name: Hsu, C. -L.
name: Iijima, T.
name: Inami, K.
name: Ipsita, N.
name: Ishikawa, A.
name: Itoh, R.
name: Iwasaki, M.
name: Jacobs, W. W.
name: Jang, E. -J.
name: Ji, Q. P.
name: Jia, S.
name: Jin, Y.
name: Joo, K. K.
name: Kalita, D.
name: Kaliyar, A. B.
name: Kawasaki, T.
name: Kiesling, C.
name: Kim, C. H.
name: Kim, D. Y.
name: Kim, K. -H.
name: Kim, Y. -K.
name: Kindo, H.
name: Kinoshita, K.
name: Kodyš, P.
name: Korpar, S.
name: Križan, P.
name: Krokovny, P.
name: Kuhr, T.
name: Kumar, M.
name: Kumar, R.
name: Kumara, K.
name: Kwon, Y. -J.
name: Lange, J. S.
name: Lee, S. C.
name: Li, J.
name: Li, L. K.
name: Libby, J.
name: Lieret, K.
name: Lin, Y. -R.
name: Liventsev, D.
name: Luo, T.
name: Ma, Y.
name: Masuda, M.
name: Matsuda, T.
name: Maurya, S. K.
name: Meier, F.
name: Merola, M.
name: Metzner, F.
name: Miyabayashi, K.
name: Mizuk, R.
name: Mohanty, G. B.
name: Mussa, R.
name: Nakao, M.
name: Narwal, D.
name: Natkaniec, Z.
name: Natochii, A.
name: Nayak, L.
name: Nayak, M.
name: Nisar, N. K.
name: Nishida, S.
name: Ogawa, S.
name: Oskin, P.
name: Pakhlova, G.
name: Pardi, S.
name: Park, H.
name: Park, J.
name: Park, S. -H.
name: Passeri, A.
name: Patra, S.
name: Paul, S.
name: Pestotnik, R.
name: Piilonen, L. E.
name: Podobnik, T.
name: Prencipe, E.
name: Prim, M. T.
name: Rabusov, A.
name: Rout, N.
name: Russo, G.
name: Sandilya, S.
name: Sangal, A.
name: Santelj, L.
name: Savinov, V.
name: Schnell, G.
name: Schwanda, C.
name: Seino, Y.
name: Senyo, K.
name: Shan, W.
name: Shapkin, M.
name: Sharma, C.
name: Shiu, J. -G.
name: Singh, J. B.
name: Sokolov, A.
name: Solovieva, E.
name: Starič, M.
name: Stottler, Z. S.
name: Sumihama, M.
name: Takizawa, M.
name: Tamponi, U.
name: Tanida, K.
name: Tenchini, F.
name: Tiwary, R.
name: Trabelsi, K.
name: Uchida, M.
name: Uglov, T.
name: Unno, Y.
name: Uno, K.
name: Uno, S.
name: Vahsen, S. E.
name: Varner, G.
name: Vinokurova, A.
name: Vossen, A.
name: Wang, D.
name: Wang, E.
name: Wang, M. -Z.
name: Watanuki, S.
name: Werbycka, O.
name: Xu, X.
name: Yabsley, B. D.
name: Yan, W.
name: Yang, S. B.
name: Yelton, J.
name: Yin, J. H.
name: Yuan, C. Z.
name: Yusa, Y.
name: Zhang, Z. P.
name: Zhilich, V.
name: Zhukova, V.
Publisher: name: arXiv
Year: 2023
Subjects: subject: High Energy Physics - Experiment (hep-ex)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We report the first measurement of the Michel parameter $ξ^\prime$ in the $τ^-\toμ^-\barν_μν_τ$ decay with a new method proposed just recently. The measurement is based on the reconstruction of the $τ^-\toμ^-\barν_μν_τ$ events with subsequent muon decay-in-flight in the Belle central drift chamber. The analyzed data sample of $988\,\text{fb}^{-1}$ collected by the Belle detector corresponds to approximately $912\times10^6$ $τ^+ τ^-$ pairs. We measure $ξ^\prime=0.22\pm0.94(\text{stat})\pm0.42(\text{syst})$, which is in agreement with the standard model prediction of $ξ^\prime=1$. Statistical uncertainty dominates in this study, being a limiting factor, while systematic uncertainty is well under control. Our analysis proved the practicability of this promising method and its prospects for further precise measurement in future experiments.
description: 6 pages, 4 figures, published in Phys. Rev. Lett