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Measurement of $B^{+} \to τ^{+} ν_{τ}$ branching fraction with a hadronic tagging method at Belle II

I. Adachi , K. Adamczyk , H. Ahmed , Y. Ahn , H. Aihara , N. Akopov , M. Alhakami , A. Aloisio , N. Althubiti et al. (Belle II Collaboration)

N. Althubiti , M. Angelsmark , N. Anh Ky , D. M. Asner , H. Atmacan , V. Aushev , M. Aversano , R. Ayad , V. Babu , N. K. Baghel , S. Bahinipati , P. Bambade , Sw. Banerjee , M. Bartl , J. Baudot , A. Baur , A. Beaubien , F. Becherer , J. Becker , J. V. Bennett , F. U. Bernlochner , V. Bertacchi , E. Bertholet , M. Bessner , S. Bettarini , B. Bhuyan , F. Bianchi , D. Biswas , A. Bobrov , D. Bodrov , A. Bondar , J. Borah , A. Boschetti , A. Bozek , M. Bračko , P. Branchini , R. A. Briere , T. E. Browder , A. Budano , S. Bussino , Q. Campagna , M. Campajola , L. Cao , G. Casarosa , C. Cecchi , M.-C. Chang , P. Cheema , B. G. Cheon , K. Chilikin , K. Chirapatpimol , H.-E. Cho , K. Cho , S.-J. Cho , S.-K. Choi , S. Choudhury , J. Cochran , L. Corona , J. X. Cui , E. De La Cruz-Burelo , S. A. De La Motte , G. De Nardo , G. De Pietro , R. de Sangro , M. Destefanis , S. Dey , A. Di Canto , J. Dingfelder , Z. Doležal , T. V. Dong , M. Dorigo , K. Dugic , G. Dujany , P. Ecker , D. Epifanov , J. Eppelt , T. Ferber , T. Fillinger , C. Finck , G. Finocchiaro , A. Fodor , F. Forti , B. G. Fulsom , A. Gabrielli , A. Gale , M. Garcia-Hernandez , L. Gärtner , G. Gaudino , V. Gaur , A. Gaz , A. Gellrich , G. Ghevondyan , D. Ghosh , H. Ghumaryan , G. Giakoustidis , R. Giordano , A. Giri , P. Gironella Gironell , B. Gobbo , R. Godang , O. Gogota , P. Goldenzweig , W. Gradl , E. Graziani , D. Greenwald , Z. Gruberová , Y. Guan , K. Gudkova , I. Haide , H. Hayashii , S. Hazra , C. Hearty , I. Heredia de la Cruz , T. Higuchi , M. Hoek , M. Hohmann , R. Hoppe , P. Horak , C.-L. Hsu , A. Huang , T. Iijima , N. Ipsita , A. Ishikawa , R. Itoh , M. Iwasaki , P. Jackson , D. Jacobi , W. W. Jacobs , D. E. Jaffe , E.-J. Jang , Y. Jin , A. Johnson , K. K. Joo , H. Junkerkalefeld , J. Kandra , K. H. Kang , G. Karyan , T. Kawasaki , C. Ketter , C. Kiesling , D. Y. Kim , J.-Y. Kim , K.-H. Kim , H. Kindo , K. Kinoshita , P. Kodyš , T. Koga , S. Kohani , K. Kojima , A. Korobov , S. Korpar , E. Kovalenko , R. Kowalewski , P. Križan , P. Krokovny , T. Kuhr , D. Kumar , R. Kumar , K. Kumara , T. Kunigo , A. Kuzmin , Y.-J. Kwon , T. Lam , J. S. Lange , T. S. Lau , M. Laurenza , R. Leboucher , F. R. Le Diberder , M. J. Lee , P. Leo , L. K. Li , W. Z. Li , Y. Li , J. Libby , S. Lin , M. H. Liu , Q. Y. Liu , Z. Q. Liu , D. Liventsev , S. Longo , T. Lueck , C. Lyu , Y. Ma , C. Madaan , M. Maggiora , R. Maiti , G. Mancinelli , R. Manfredi , E. Manoni , M. Mantovano , D. Marcantonio , S. Marcello , C. Marinas , C. Martellini , A. Martens , T. Martinov , L. Massaccesi , M. Masuda , K. Matsuoka , S. K. Maurya , M. Maushart , J. A. McKenna , F. Meier , D. Meleshko , M. Merola , C. Miller , M. Mirra , K. Miyabayashi , R. Mizuk , S. Mondal , S. Moneta , H.-G. Moser , I. Nakamura , M. Nakao , H. Nakazawa , Z. Natkaniec , A. Natochii , M. Nayak , M. Neu , M. Niiyama , S. Nishida , S. Ogawa , R. Okubo , H. Ono , G. Pakhlova , S. Pardi , J. Park , K. Park , S.-H. Park , B. Paschen , S. Patra , S. Paul , T. K. Pedlar , I. Peruzzi , R. Peschke , L. E. Piilonen , T. Podobnik , S. Pokharel , C. Praz , S. Prell , E. Prencipe , M. T. Prim , S. Privalov , I. Prudiiev , H. Purwar , S. Raiz , K. Ravindran , J. U. Rehman , M. Reif , S. Reiter , M. Remnev , D. Ricalde Herrmann , I. Ripp-Baudot , G. Rizzo , S. H. Robertson , J. M. Roney , A. Rostomyan , N. Rout , D. A. Sanders , S. Sandilya , L. Santelj , V. Savinov , B. Scavino , C. Schmitt , J. Schmitz , S. Schneider , C. Schwanda , Y. Seino , K. Senyo , M. E. Sevior , C. Sfienti , W. Shan , X. D. Shi , T. Shillington , J.-G. Shiu , D. Shtol , A. Sibidanov , F. Simon , J. B. Singh , J. Skorupa , R. J. Sobie , M. Sobotzik , A. Soffer , A. Sokolov , E. Solovieva , S. Spataro , B. Spruck , M. Starič , S. Stefkova , R. Stroili , Y. Sue , M. Sumihama , M. Takizawa , F. Tenchini , A. Thaller , O. Tittel , R. Tiwary , E. Torassa , K. Trabelsi , I. Tsaklidis , I. Ueda , T. Uglov , K. Unger , K. Uno , S. Uno , P. Urquijo , Y. Ushiroda , S. E. Vahsen , R. van Tonder , K. E. Varvell , M. Veronesi , A. Vinokurova , V. S. Vismaya , V. Vobbilisetti , R. Volpe , S. Wallner , M.-Z. Wang , A. Warburton , S. Watanuki , C. Wessel , E. Won , X. P. Xu , B. D. Yabsley , S. Yamada , W. Yan , S. B. Yang , J. Yelton , J. H. Yin , K. Yoshihara , C. Z. Yuan , J. Yuan , L. Zani , F. Zeng , B. Zhang , V. Zhilich , Q. D. Zhou , L. Zhu , and R. Žlebčík (Belle II Collaboration)

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Phys. Rev. D 112, 072002 – Published 3 October, 2025

DOI: https://doi.org/10.1103/dcwd-5tg4

Abstract

We present a measurement of the branching fraction of $B^{+} \to τ^{+} ν_{τ}$ decays using $387 \pm 6 \times 10^{6}$ $ϒ (4 S)$ collected between 2019 and 2022 with the Belle II detector at the SuperKEKB $e^{+} e^{-}$ collider. We reconstruct the accompanying $B^{-}$ meson using the hadronic tagging method, while $B^{+} \to τ^{+} ν_{τ}$ candidates are identified in the recoil. We find evidence for $B^{+} \to τ^{+} ν_{τ}$ decays at 3.0 standard deviations, including systematic uncertainties. The measured branching fraction is $B (B^{+} \to τ^{+} ν_{τ}) = [1.24 \pm 0.41 (stat) \pm 0.19 (syst)] \times 10^{- 4}$ .

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References (38)

Throughout this paper, the inclusion of the charge-conjugate decay mode is implied unless otherwise stated.
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Phys. Rev. D 112, 072002– Published 3 October, 2025

Vol. 112, Iss. 7 — 1 October 2025

Received 7 February 2025
Accepted 10 September 2025

DOI: https://doi.org/10.1103/dcwd-5tg4

Published by the American Physical Society under the terms of the 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.

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Measurement of $B^{+} \to τ^{+} ν_{τ}$ branching fraction with a hadronic tagging method at Belle II

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Measurement of B+→τ+ντ branching fraction with a hadronic tagging method at Belle II

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Measurement of $B^{+} \to τ^{+} ν_{τ}$ branching fraction with a hadronic tagging method at Belle II