Updated measurement of the branching fraction of D_s⁺ → τ⁺ ν_τ

@misc{collaboration2026updated,
  title = {{Updated measurement of the branching fraction of $D_s^+ \to τ^+ ν_τ$}},
  author = {BESIII Collaboration and M. Ablikim and M. N. Achasov and P. Adlarson and X. C. Ai and C. S. Akondi and R. Aliberti and A. Amoroso and Q. An and Y. H. An and Y. Bai and O. Bakina and Y. Ban and H. -R. Bao and X. L. Bao and V. Batozskaya and K. Begzsuren and N. Berger and M. Berlowski and M. B. Bertani and D. Bettoni and F. Bianchi and E. Bianco and A. Bortone and I. Boyko and R. A. Briere and A. Brueggemann and H. Cai and M. H. Cai and X. Cai and A. Calcaterra and G. F. Cao and N. Cao and S. A. Cetin and X. Y. Chai and J. F. Chang and T. T. Chang and G. R. Che and Y. Z. Che and C. H. Chen and Chao Chen and G. Chen and H. S. Chen and H. Y. Chen and M. L. Chen and S. J. Chen and S. M. Chen and T. Chen and W. Chen and X. R. Chen and X. T. Chen and X. Y. Chen and Y. B. Chen and Y. Q. Chen and Z. K. Chen and J. Cheng and L. N. Cheng and S. K. Choi and X. Chu and G. Cibinetto},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2606.11593},
  eprint = {2606.11593},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2606.11593},
}

TY  - UNPB
TI  - Updated measurement of the branching fraction of D_s^+ → τ^+ ν_τ
AU  - BESIII Collaboration
AU  - M. Ablikim
AU  - M. N. Achasov
AU  - P. Adlarson
AU  - X. C. Ai
AU  - C. S. Akondi
AU  - R. Aliberti
AU  - A. Amoroso
AU  - Q. An
AU  - Y. H. An
AU  - Y. Bai
AU  - O. Bakina
AU  - Y. Ban
AU  - H. -R. Bao
AU  - X. L. Bao
AU  - V. Batozskaya
AU  - K. Begzsuren
AU  - N. Berger
AU  - M. Berlowski
AU  - M. B. Bertani
AU  - D. Bettoni
AU  - F. Bianchi
AU  - E. Bianco
AU  - A. Bortone
AU  - I. Boyko
AU  - R. A. Briere
AU  - A. Brueggemann
AU  - H. Cai
AU  - M. H. Cai
AU  - X. Cai
AU  - A. Calcaterra
AU  - G. F. Cao
AU  - N. Cao
AU  - S. A. Cetin
AU  - X. Y. Chai
AU  - J. F. Chang
AU  - T. T. Chang
AU  - G. R. Che
AU  - Y. Z. Che
AU  - C. H. Chen
AU  - Chao Chen
AU  - G. Chen
AU  - H. S. Chen
AU  - H. Y. Chen
AU  - M. L. Chen
AU  - S. J. Chen
AU  - S. M. Chen
AU  - T. Chen
AU  - W. Chen
AU  - X. R. Chen
AU  - X. T. Chen
AU  - X. Y. Chen
AU  - Y. B. Chen
AU  - Y. Q. Chen
AU  - Z. K. Chen
AU  - J. Cheng
AU  - L. N. Cheng
AU  - S. K. Choi
AU  - X. Chu
AU  - G. Cibinetto
PY  - 2026
DA  - 2026/10/05
PB  - arXiv
DO  - 10.48550/arxiv.2606.11593
UR  - https://arxiv.org/abs/2606.11593
AB  - Using a dataset of 7.33 fb^−1 of e^+ e^- annihilation data collected with the BESIII detector at center-of-mass energies from 4.128 to 4.226 GeV, we report an updated measurement of the branching fraction of D_s^+ → τ^+ ν_τ via four τ^+ decay modes: τ^+ → e^+ ν_e ν̅_τ, μ^+ ν_μ ν̅_τ, π^+ν̅_τ, and π^+ π^0 ν̅_τ. The branching fraction is determined to be ℬ(D_s^+ → τ^+ ν_τ) = (5.37 ± 0.08_stat ± 0.06_syst) %. The product of the modulus of the Cabibbo-Kobayashi-Maskawa matrix element |V_cs| and the D_s^+ decay constant f_D_s^+ is measured to be f_D_s^+ |V_cs| = (248.2 ± 1.9_stat ± 1.4_syst ± 0.6_input ± 0.8_EM) MeV. Both the branching fraction and the product f_D_s^+ |V_cs| are the most precise results yet obtained. Then, taking f_D_s^+ from lattice quantum chromodynamics calculations results in |V_cs| = 0.993 ± 0.008_stat ± 0.006_syst ± 0.003_input ± 0.003_EM. Conversely, one finds f_D_s^+ = (255.0 ± 1.9_stat ± 1.4_syst ± 0.6_input ± 0.8_EM) MeV when taking |V_cs| from the CKMfitter group as an input. Combining with the world average value of D_s^+ → μ^+ ν_μ, the ratio of the branching fractions between D_s^+ → τ^+ ν_τ and D_s^+ → μ^+ ν_μ is estimated to be 10.04 ± 0.29, which is consistent with the Standard Model prediction of lepton flavor universality.
ER  -