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Test of lepton flavor universality with measurements of $R (D^{+})$ and $R (D^{* +})$ using semileptonic $B$ tagging at the Belle II experiment

I. Adachi , K. Adamczyk , L. Aggarwal , H. Ahmed , H. Aihara , N. Akopov , S. Alghamdi , M. Alhakami , A. Aloisio et al. (Belle II Collaboration)

A. Aloisio , N. Althubiti , K. Amos , M. Angelsmark , N. Anh Ky , C. Antonioli , D. M. Asner , H. Atmacan , T. Aushev , V. Aushev , M. Aversano , R. Ayad , V. Babu , H. Bae , N. K. Baghel , S. Bahinipati , P. Bambade , Sw. Banerjee , S. Bansal , M. Barrett , M. Bartl , J. Baudot , A. Beaubien , F. Becherer , J. Becker , J. V. Bennett , F. U. Bernlochner , V. Bertacchi , M. Bertemes , E. Bertholet , M. Bessner , S. Bettarini , V. Bhardwaj , B. Bhuyan , F. Bianchi , T. Bilka , D. Biswas , A. Bobrov , D. Bodrov , A. Bolz , 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 , J. Cerasoli , M.-C. Chang , P. Chang , R. Cheaib , P. Cheema , B. G. Cheon , K. Chilikin , J. Chin , K. Chirapatpimol , H.-E. Cho , K. Cho , S.-J. Cho , S.-K. Choi , S. Choudhury , J. Cochran , I. Consigny , 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 , R. Dhamija , F. Di Capua , J. Dingfelder , Z. Doležal , I. Domínguez Jiménez , T. V. Dong , M. Dorigo , D. Dossett , S. Dubey , K. Dugic , G. Dujany , P. Ecker , D. Epifanov , P. Feichtinger , T. Ferber , T. Fillinger , C. Finck , G. Finocchiaro , A. Fodor , F. Forti , B. G. Fulsom , A. Gabrielli , A. Gale , E. Ganiev , M. Garcia-Hernandez , R. Garg , G. Gaudino , V. Gaur , V. Gautam , A. Gaz , A. Gellrich , G. Ghevondyan , D. Ghosh , H. Ghumaryan , G. Giakoustidis , R. Giordano , A. Giri , P. Gironella Gironell , A. Glazov , B. Gobbo , R. Godang , O. Gogota , P. Goldenzweig , W. Gradl , S. Granderath , E. Graziani , D. Greenwald , Z. Gruberová , Y. Guan , K. Gudkova , I. Haide , Y. Han , K. Hara , T. Hara , C. Harris , K. Hayasaka , H. Hayashii , S. Hazra , C. Hearty , M. T. Hedges , I. Heredia de la Cruz , M. Hernández Villanueva , T. Higuchi , M. Hoek , M. Hohmann , R. Hoppe , P. Horak , C.-L. Hsu , A. Huang , T. Humair , T. Iijima , K. Inami , G. Inguglia , N. Ipsita , A. Ishikawa , R. Itoh , M. Iwasaki , P. Jackson , D. Jacobi , W. W. Jacobs , D. E. Jaffe , E.-J. Jang , Q. P. Ji , S. Jia , Y. Jin , A. Johnson , K. K. Joo , H. Junkerkalefeld , A. B. Kaliyar , J. Kandra , K. H. Kang , S. Kang , G. Karyan , T. Kawasaki , F. Keil , C. Ketter , M. Khan , C. Kiesling , C.-H. Kim , D. Y. Kim , J.-Y. Kim , K.-H. Kim , Y.-K. Kim , H. Kindo , K. Kinoshita , P. Kodyš , T. Koga , S. Kohani , K. Kojima , A. Korobov , S. Korpar , R. Kowalewski , P. Križan , P. Krokovny , T. Kuhr , Y. Kulii , D. Kumar , J. Kumar , K. Kumara , T. Kunigo , A. Kuzmin , Y.-J. Kwon , S. Lacaprara , Y.-T. Lai , K. Lalwani , T. Lam , J. S. Lange , T. S. Lau , M. Laurenza , R. Leboucher , F. R. Le Diberder , M. J. Lee , C. Lemettais , P. Leo , P. M. Lewis , C. Li , H.-J. Li , L. K. Li , Q. M. Li , W. Z. Li , Y. B. Li , Y. P. Liao , J. Libby , J. Lin , S. Lin , M. H. Liu , Q. Y. Liu , Y. Liu , Z. Q. Liu , D. Liventsev , S. Longo , T. Lueck , C. Lyu , Y. Ma , C. Madaan , M. Maggiora , S. P. Maharana , R. Maiti , G. Mancinelli , R. Manfredi , E. Manoni , A. C. Manthei , M. Mantovano , D. Marcantonio , S. Marcello , C. Marinas , C. Martellini , A. Martens , A. Martini , T. Martinov , L. Massaccesi , M. Masuda , D. Matvienko , S. K. Maurya , M. Maushart , J. A. McKenna , R. Mehta , F. Meier , D. Meleshko , M. Merola , F. Metzner , C. Miller , M. Mirra , S. Mitra , K. Miyabayashi , H. Miyake , R. Mizuk , G. B. Mohanty , S. Mondal , S. Moneta , A. L. Moreira de Carvalho , H.-G. Moser , I. Nakamura , K. R. Nakamura , M. Nakao , Y. Nakazawa , M. Naruki , Z. Natkaniec , A. Natochii , M. Nayak , G. Nazaryan , M. Neu , S. Nishida , A. Novosel , S. Ogawa , R. Okubo , H. Ono , Y. Onuki , F. Otani , G. Pakhlova , E. Paoloni , S. Pardi , K. Parham , H. Park , J. Park , K. Park , S.-H. Park , B. Paschen , A. Passeri , S. Patra , T. K. Pedlar , I. Peruzzi , R. Peschke , R. Pestotnik , M. Piccolo , L. E. Piilonen , P. L. M. Podesta-Lerma , T. Podobnik , S. Pokharel , A. Prakash , C. Praz , S. Prell , E. Prencipe , M. T. Prim , S. Privalov , I. Prudiiev , H. Purwar , P. Rados , G. Raeuber , S. Raiz , V. Raj , N. Rauls , K. Ravindran , J. U. Rehman , M. Reif , S. Reiter , M. Remnev , L. Reuter , D. Ricalde Herrmann , I. Ripp-Baudot , G. Rizzo , S. H. Robertson , M. Roehrken , J. M. Roney , A. Rostomyan , N. Rout , L. Salutari , D. A. Sanders , S. Sandilya , L. Santelj , C. Santos , V. Savinov , B. Scavino , C. Schmitt , J. Schmitz , S. Schneider , C. Schwanda , A. J. Schwartz , Y. Seino , A. Selce , K. Senyo , J. Serrano , M. E. Sevior , C. Sfienti , W. Shan , C. Sharma , G. Sharma , X. D. Shi , T. Shillington , T. Shimasaki , 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 , W. Song , S. Spataro , B. Spruck , M. Starič , P. Stavroulakis , S. Stefkova , R. Stroili , J. Strube , Y. Sue , M. Sumihama , K. Sumisawa , W. Sutcliffe , N. Suwonjandee , H. Svidras , M. Takahashi , M. Takizawa , U. Tamponi , K. Tanida , F. Tenchini , A. Thaller , O. Tittel , R. Tiwary , E. Torassa , K. Trabelsi , I. Tsaklidis , M. Uchida , I. Ueda , T. Uglov , K. Unger , Y. Unno , K. Uno , S. Uno , P. Urquijo , Y. Ushiroda , S. E. Vahsen , R. van Tonder , K. E. Varvell , M. Veronesi , A. Vinokurova , V. S. Vismaya , L. Vitale , V. Vobbilisetti , R. Volpe , A. Vossen , M. Wakai , S. Wallner , M.-Z. Wang , X. L. Wang , Z. Wang , A. Warburton , M. Watanabe , S. Watanuki , C. Wessel , E. Won , X. P. Xu , B. D. Yabsley , S. Yamada , W. Yan , W. C. Yan , J. Yelton , J. H. Yin , K. Yoshihara , C. Z. Yuan , J. Yuan , L. Zani , F. Zeng , M. Zeyrek , B. Zhang , J. S. Zhou , Q. D. Zhou , L. Zhu , V. I. Zhukova , and R. Žlebčík (Belle II Collaboration)

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Phys. Rev. D 112, 032010 – Published 26 August, 2025

DOI: https://doi.org/10.1103/fmn3-h8fy

Abstract

We report measurements of the ratios of branching fractions $R (D^{(*) +}) = B ({\bar{B}}^{0} \to D^{(*) +} τ^{-} {\bar{ν}}_{τ}) / B ({\bar{B}}^{0} \to D^{(*) +} ℓ^{-} {\bar{ν}}_{ℓ})$ , where $ℓ$ denotes either an electron or a muon. These ratios test the universality of the charged-current weak interaction. The results are based on a $365 {fb}^{- 1}$ data sample collected with the Belle II detector at the SuperKEKB $e^{+} e^{-}$ collider, which operates at a center-of-mass energy corresponding to the $ϒ (4 S)$ resonance, just above the threshold for $B \bar{B}$ production. Signal candidates are reconstructed by selecting events in which the companion $B$ meson from the $ϒ (4 S) \to B \bar{B}$ decay is identified in semileptonic modes. The $τ$ lepton is reconstructed via its leptonic decays. We obtain $R (D^{+}) = {0.418}_{- 0.073}^{+ 0.075} {(stat)}_{- 0.056}^{+ 0.049} (syst)$ and $R (D^{* +}) = {0.306}_{- 0.033}^{+ 0.035} {(stat)}_{- 0.018}^{+ 0.016} (syst)$ , which are consistent with world average values. Accounting for the correlation between them, these values differ from the Standard Model expectation by a collective significance of 1.7 standard deviations.

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Phys. Rev. D 112, 032010– Published 26 August, 2025

Vol. 112, Iss. 3 — 1 August 2025

Received 16 April 2025
Accepted 16 July 2025

DOI: https://doi.org/10.1103/fmn3-h8fy

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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Test of lepton flavor universality with measurements of $R (D^{+})$ and $R (D^{* +})$ using semileptonic $B$ tagging at the Belle II experiment

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Test of lepton flavor universality with measurements of R(D+) and R(D*+) using semileptonic B tagging at the Belle II experiment

Abstract

Physics Subject Headings (PhySH)

Article Text

References (57)

Test of lepton flavor universality with measurements of $R (D^{+})$ and $R (D^{* +})$ using semileptonic $B$ tagging at the Belle II experiment