Test of lepton flavor universality with B̅ → D^(*) τ⁻ ν̅_τ and B̅ → D^(*) ℓ⁻ ν̅_ℓ decays at Belle II

@misc{collaboration2026test,
  title = {{Test of lepton flavor universality with $\barB \rightarrow D^(*) τ^- \barν_τ$ and $\barB \rightarrow D^(*) \ell^- \barν_\ell$ decays at Belle II}},
  author = {Belle II Collaboration and M. Abumusabh and I. Adachi and K. Adamczyk and A. Aggarwal and L. Aggarwal and H. Ahmed and Y. Ahn and H. Aihara and M. Akdag and N. Akopov and A. Akram and S. Alghamdi and M. Alhakami and A. Aloisio and N. Althubiti and K. Amos and M. Angelsmark and N. Anh Ky and C. Antonioli and K. Arai and D. M. Asner and H. Atmacan and T. Aushev and V. Aushev and R. Ayad and V. Babu and H. Bae and N. K. Baghel and S. Bahinipati and P. Bambade and Sw. Banerjee and S. Bansal and M. Barrett and M. Bartl and J. Baudot and A. Baur and A. Beaubien and F. Becherer and J. Becker and J. V. Bennett and F. U. Bernlochner and V. Bertacchi and M. Bertemes and E. Bertholet and M. Bessner and S. Bettarini and V. Bhardwaj and B. Bhuyan and F. Bianchi and T. Bilka and A. Biswas and D. Biswas and A. Bobrov and D. Bodrov and A. Bondar and G. Bonvicini and J. Borah and A. Boschetti and A. Bozek},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.21947},
  eprint = {2609.21947},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.21947},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Test of lepton flavor universality with B̅ → D^(*) τ^− ν̅_τ and B̅ → D^(*) ℓ^− ν̅_ℓ decays at Belle II
AU  - Belle II Collaboration
AU  - M. Abumusabh
AU  - I. Adachi
AU  - K. Adamczyk
AU  - A. Aggarwal
AU  - L. Aggarwal
AU  - H. Ahmed
AU  - Y. Ahn
AU  - H. Aihara
AU  - M. Akdag
AU  - N. Akopov
AU  - A. Akram
AU  - S. Alghamdi
AU  - M. Alhakami
AU  - A. Aloisio
AU  - N. Althubiti
AU  - K. Amos
AU  - M. Angelsmark
AU  - N. Anh Ky
AU  - C. Antonioli
AU  - K. Arai
AU  - D. M. Asner
AU  - H. Atmacan
AU  - T. Aushev
AU  - V. Aushev
AU  - R. Ayad
AU  - V. Babu
AU  - H. Bae
AU  - N. K. Baghel
AU  - S. Bahinipati
AU  - P. Bambade
AU  - Sw. Banerjee
AU  - S. Bansal
AU  - M. Barrett
AU  - M. Bartl
AU  - J. Baudot
AU  - A. Baur
AU  - A. Beaubien
AU  - F. Becherer
AU  - J. Becker
AU  - J. V. Bennett
AU  - F. U. Bernlochner
AU  - V. Bertacchi
AU  - M. Bertemes
AU  - E. Bertholet
AU  - M. Bessner
AU  - S. Bettarini
AU  - V. Bhardwaj
AU  - B. Bhuyan
AU  - F. Bianchi
AU  - T. Bilka
AU  - A. Biswas
AU  - D. Biswas
AU  - A. Bobrov
AU  - D. Bodrov
AU  - A. Bondar
AU  - G. Bonvicini
AU  - J. Borah
AU  - A. Boschetti
AU  - A. Bozek
PY  - 2026
DA  - 2026/09/18
PB  - arXiv
DO  - 10.48550/arxiv.2609.21947
UR  - https://arxiv.org/abs/2609.21947
AB  - We test lepton flavor universality with a measurement of the branching-fraction ratios R(D^(*)) ≡ ℬ(B̅ → D^(*) τ^− ν̅_τ)/ℬ(B̅ → D^(*) ℓ^− ν̅_ℓ), where ℓ denotes an electron or muon. The analysis uses 387× 10^6 Υ(4S) decays collected with the Belle II detector in energy-asymmetric e^+e^- collisions. One B meson is fully reconstructed in a hadronic decay mode, while the other is reconstructed either in B̅→ D^(*)τ^−ν̅_τ, with τ^- → ℓ^- ν̅_ℓν_τ, or in B̅→ D^(*)ℓ^−ν̅_ℓ. We extract the signal from the distributions of the residual calorimeter energy and the squared mass of the undetected particles, obtaining R(D^*) = 0.242 ±0.019(stat) ±0.016(syst) and R(D) = 0.439 ± 0.055(stat) ± 0.046(syst). These results are consistent with both the standard model predictions and previous measurements, and constitute the most precise determination of R(D^(*)) with hadronic tagging.
ER  -