Test of light-lepton universality in $τ$ decays with the Belle II experiment
Creators: name: Belle II Collaboration
name: Adachi, I.
name: Adamczyk, K.
name: Aggarwal, L.
name: Aihara, H.
name: Akopov, N.
name: Aloisio, A.
name: Ky, N. Anh
name: Asner, D. M.
name: Atmacan, H.
name: Aushev, V.
name: Aversano, M.
name: Ayad, R.
name: Babu, V.
name: Bae, H.
name: Bahinipati, S.
name: Bambade, P.
name: Banerjee, Sw.
name: Bansal, S.
name: Barrett, M.
name: Baudot, J.
name: Baur, A.
name: Beaubien, A.
name: Becherer, F.
name: Becker, J.
name: Bennett, J. V.
name: Bernlochner, F. U.
name: Bertacchi, V.
name: Bertemes, M.
name: Bertholet, E.
name: Bessner, M.
name: Bettarini, S.
name: Bianchi, F.
name: Bierwirth, L.
name: Bilka, T.
name: Bilokin, S.
name: Biswas, D.
name: Bobrov, A.
name: Bodrov, D.
name: Bolz, A.
name: Borah, J.
name: Boschetti, A.
name: Bozek, A.
name: Bračko, M.
name: Branchini, P.
name: Browder, T. E.
name: Budano, A.
name: Bussino, S.
name: Campajola, M.
name: Cao, L.
name: Casarosa, G.
name: Cecchi, C.
name: Cerasoli, J.
name: Chang, M. -C.
name: Chang, P.
name: Cheaib, R.
name: Cheema, P.
name: Cheon, B. G.
name: Chilikin, K.
name: Chirapatpimol, K.
name: Cho, H. -E.
name: Cho, K.
name: Cho, S. -J.
name: Choi, S. -K.
name: Choudhury, S.
name: Corona, L.
name: Cui, J. X.
name: Das, S.
name: Dattola, F.
name: De La Cruz-Burelo, E.
name: De La Motte, S. A.
name: de Marino, G.
name: De Nardo, G.
name: De Nuccio, M.
name: De Pietro, G.
name: de Sangro, R.
name: Destefanis, M.
name: Dey, S.
name: Dhamija, R.
name: Di Canto, A.
name: Di Capua, F.
name: Dingfelder, J.
name: Doležal, Z.
name: Jiménez, I. Domínguez
name: Dong, T. V.
name: Dorigo, M.
name: Dorner, D.
name: Dort, K.
name: Dossett, D.
name: Dreyer, S.
name: Dubey, S.
name: Dugic, K.
name: Dujany, G.
name: Ecker, P.
name: Eliachevitch, M.
name: Epifanov, D.
name: Feichtinger, P.
name: Ferber, T.
name: Ferlewicz, D.
name: Fillinger, T.
name: Finck, C.
name: Finocchiaro, G.
name: Fodor, A.
name: Forti, F.
name: Frey, A.
name: Fulsom, B. G.
name: Gabrielli, A.
name: Ganiev, E.
name: Garcia-Hernandez, M.
name: Gaudino, G.
name: Gaur, V.
name: Gaz, A.
name: Gellrich, A.
name: Ghevondyan, G.
name: Ghosh, D.
name: Ghumaryan, H.
name: Giakoustidis, G.
name: Giordano, R.
name: Giri, A.
name: Glazov, A.
name: Gobbo, B.
name: Godang, R.
name: Gogota, O.
name: Goldenzweig, P.
name: Gradl, W.
name: Grammatico, T.
name: Granderath, S.
name: Graziani, E.
name: Greenwald, D.
name: Gruberová, Z.
name: Gu, T.
name: Guan, Y.
name: Gudkova, K.
name: Han, Y.
name: Hara, T.
name: Hayasaka, K.
name: Hayashii, H.
name: Hazra, S.
name: Hearty, C.
name: Hedges, M. T.
name: Heidelbach, A.
name: de la Cruz, I. Heredia
name: Villanueva, M. Hernández
name: Higuchi, T.
name: Hoek, M.
name: Hohmann, M.
name: Horak, P.
name: Hsu, C. -L.
name: Humair, T.
name: Iijima, T.
name: Inami, K.
name: Inguglia, G.
name: Ipsita, N.
name: Ishikawa, A.
name: Itoh, R.
name: Iwasaki, M.
name: Jacobs, W. W.
name: Jaffe, D. E.
name: Jang, E. -J.
name: Ji, Q. P.
name: Jia, S.
name: Jin, Y.
name: Junkerkalefeld, H.
name: Kaleta, M.
name: Kalita, D.
name: Kaliyar, A. B.
name: Kandra, J.
name: Kang, S.
name: Karyan, G.
name: Kawasaki, T.
name: Keil, F.
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: Koga, T.
name: Kohani, S.
name: Kojima, K.
name: Konno, T.
name: Korobov, A.
name: Korpar, S.
name: Kovalenko, E.
name: Kowalewski, R.
name: Kraetzschmar, T. M. G.
name: Križan, P.
name: Krokovny, P.
name: Kuhr, T.
name: Kulii, Y.
name: Kumar, J.
name: Kumar, M.
name: Kumara, K.
name: Kunigo, T.
name: Kuzmin, A.
name: Kwon, Y. -J.
name: Lacaprara, S.
name: Lai, Y. -T.
name: Lalwani, K.
name: Lam, T.
name: Lanceri, L.
name: Lange, J. S.
name: Laurenza, M.
name: Lautenbach, K.
name: Leboucher, R.
name: Diberder, F. R. Le
name: Lee, M. J.
name: Leo, P.
name: Lemettais, C.
name: Levit, D.
name: Lewis, P. M.
name: Li, C.
name: Li, L. K.
name: Li, S. X.
name: Li, Y.
name: Li, Y. B.
name: Libby, J.
name: Liptak, Z.
name: Liu, M. H.
name: Liu, Q. Y.
name: Liu, Y.
name: Liu, Z. Q.
name: Liventsev, D.
name: Longo, S.
name: Lueck, T.
name: Lyu, C.
name: Ma, Y.
name: Maggiora, M.
name: Maharana, S. P.
name: Maiti, R.
name: Maity, S.
name: Mancinelli, G.
name: Manfredi, R.
name: Manoni, E.
name: Mantovano, M.
name: Marcantonio, D.
name: Marcello, S.
name: Marinas, C.
name: Martellini, C.
name: Martini, A.
name: Martinov, T.
name: Massaccesi, L.
name: Masuda, M.
name: Matsuoka, K.
name: Matvienko, D.
name: Maurya, S. K.
name: McKenna, J. A.
name: Mehta, R.
name: Meier, F.
name: Merola, M.
name: Metzner, F.
name: Miller, C.
name: Mirra, M.
name: Mitra, S.
name: Miyabayashi, K.
name: Miyake, H.
name: Mizuk, R.
name: Mohanty, G. B.
name: Mondal, S.
name: Moneta, S.
name: Moser, H. -G.
name: Mrvar, M.
name: Mussa, R.
name: Nakamura, I.
name: Nakamura, K. R.
name: Nakao, M.
name: Nakazawa, H.
name: Nakazawa, Y.
name: Charan, A. Narimani
name: Naruki, M.
name: Narwal, D.
name: Natkaniec, Z.
name: Natochii, A.
name: Nayak, L.
name: Nayak, M.
name: Nazaryan, G.
name: Neu, M.
name: Niebuhr, C.
name: Ninkovic, J.
name: Nishida, S.
name: Novosel, A.
name: Ogawa, S.
name: Onishchuk, Y.
name: Ono, H.
name: Otani, F.
name: Pakhlov, P.
name: Pakhlova, G.
name: Panta, A.
name: Pardi, S.
name: Parham, K.
name: Park, H.
name: Park, S. -H.
name: Paschen, B.
name: Passeri, A.
name: Patra, S.
name: Pedlar, T. K.
name: Peschke, R.
name: Pestotnik, R.
name: Piccolo, M.
name: Piilonen, L. E.
name: Angioni, G. Pinna
name: Podesta-Lerma, P. L. M.
name: Podobnik, T.
name: Pokharel, S.
name: Praz, C.
name: Prell, S.
name: Prencipe, E.
name: Prim, M. T.
name: Prudiiev, I.
name: Purwar, H.
name: Rados, P.
name: Raeuber, G.
name: Raiz, S.
name: Rauls, N.
name: Reif, M.
name: Reiter, S.
name: Remnev, M.
name: Ripp-Baudot, I.
name: Rizzo, G.
name: Robertson, S. H.
name: Roehrken, M.
name: Roney, J. M.
name: Rostomyan, A.
name: Rout, N.
name: Russo, G.
name: Sanders, D. A.
name: Sandilya, S.
name: Santelj, L.
name: Sato, Y.
name: Savinov, V.
name: Scavino, B.
name: Schmitt, C.
name: Schwanda, C.
name: Schwickardi, M.
name: Seino, Y.
name: Selce, A.
name: Senyo, K.
name: Serrano, J.
name: Sevior, M. E.
name: Sfienti, C.
name: Shan, W.
name: Shi, X. D.
name: Shillington, T.
name: Shiu, J. -G.
name: Shtol, D.
name: Shwartz, B.
name: Sibidanov, A.
name: Simon, F.
name: Singh, J. B.
name: Skorupa, J.
name: Sobie, R. J.
name: Sobotzik, M.
name: Soffer, A.
name: Sokolov, A.
name: Solovieva, E.
name: Spataro, S.
name: Spruck, B.
name: Starič, M.
name: Stavroulakis, P.
name: Stefkova, S.
name: Stroili, R.
name: Sue, Y.
name: Sumihama, M.
name: Sumisawa, K.
name: Sutcliffe, W.
name: Suwonjandee, N.
name: Svidras, H.
name: Takahashi, M.
name: Takizawa, M.
name: Tamponi, U.
name: Tanaka, S.
name: Tanida, K.
name: Tenchini, F.
name: Thaller, A.
name: Tittel, O.
name: Tiwary, R.
name: Tonelli, D.
name: Torassa, E.
name: Trabelsi, K.
name: Tsaklidis, I.
name: Uchida, M.
name: Ueda, I.
name: Uglov, T.
name: Unger, K.
name: Unno, Y.
name: Uno, K.
name: Uno, S.
name: Urquijo, P.
name: Ushiroda, Y.
name: Vahsen, S. E.
name: van Tonder, R.
name: Varvell, K. E.
name: Veronesi, M.
name: Vinokurova, A.
name: Vismaya, V. S.
name: Vitale, L.
name: Vobbilisetti, V.
name: Volpe, R.
name: Wach, B.
name: Wakai, M.
name: Wallner, S.
name: Wang, E.
name: Wang, M. -Z.
name: Wang, X. L.
name: Wang, Z.
name: Warburton, A.
name: Watanabe, M.
name: Watanuki, S.
name: Wessel, C.
name: Won, E.
name: Xu, X. P.
name: Yabsley, B. D.
name: Yamada, S.
name: Yan, W.
name: Yang, S. B.
name: Yelton, J.
name: Yin, J. H.
name: Yoshihara, K.
name: Yuan, C. Z.
name: Yusa, Y.
name: Zani, L.
name: Zeng, F.
name: Zhang, B.
name: Zhang, Y.
name: Zhilich, V.
name: Zhou, Q. D.
name: Zhou, X. Y.
name: Zhukova, V. I.
name: Žlebčík, R.
Publisher: name: arXiv
Year: 2024
Subjects: subject: High Energy Physics - Experiment (hep-ex)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We present a measurement of the ratio $R_μ= \mathcal{B}(τ^-\to μ^-\barν_μν_τ) / \mathcal{B}(τ^-\to e^-\barν_eν_τ)$ of branching fractions $\mathcal{B}$ of the $τ$ lepton decaying to muons or electrons using data collected with the Belle II detector at the SuperKEKB $e^+e^-$ collider. The sample has an integrated luminosity of $362\!\pm\!2\,\text{fb}^{-1}$ at a centre-of-mass energy of $10.58\,\text{GeV}$. Using an optimised event selection, a binned maximum likelihood fit is performed using the momentum spectra of the electron and muon candidates. The result, $R_μ= 0.9675 \pm 0.0007 \pm 0.0036$, where the first uncertainty is statistical and the second is systematic, is the most precise to date. It provides a stringent test of the light-lepton universality, translating to a ratio of the couplings of the muon and electron to the $W$ boson in $τ$ decays of $0.9974 \pm 0.0019$, in agreement with the standard model expectation of unity.
description: 22 pages, 7 figures