Precision measurement of the J/ψ→μ⁺μ^-μ⁺μ^- branching fraction and search for a new gauge boson Z^′ at BESIII

@misc{collaboration2026precision,
  title = {{Precision measurement of the $J/ψ\toμ^+μ^-μ^+μ^-$ branching fraction and search for a new gauge boson $Z^\prime$ at BESIII}},
  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 M. S. Anderson and Y. Bai and O. Bakina and H. R. Bao and X. L. Bao and M. Barbagiovanni 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 D. Cabiati 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},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.37258},
  eprint = {2610.37258},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.37258},
  note = {CC BY-NC-ND 4.0},
}

TY  - UNPB
TI  - Precision measurement of the J/ψ→μ^+μ^-μ^+μ^- branching fraction and search for a new gauge boson Z^′ at BESIII
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  - M. S. Anderson
AU  - Y. Bai
AU  - O. Bakina
AU  - H. R. Bao
AU  - X. L. Bao
AU  - M. Barbagiovanni
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  - D. Cabiati
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
PY  - 2026
DA  - 2026/10/27
PB  - arXiv
DO  - 10.48550/arxiv.2610.37258
UR  - https://arxiv.org/abs/2610.37258
AB  - We present a precision measurement of the branching fraction of the rare decay J/ψ→μ^+μ^-μ^+μ^-, and a search for a new gauge boson Z^′ that couples only to the second and third lepton generations, using a data sample of (8998 ± 39) × 10^6 J/ψ events collected by the BESIII detector. The branching fraction of the J/ψ→μ^+μ^-μ^+μ^- decay is measured to be B(J/ψ→μ^+μ^-μ^+μ^-)=[0.91±0.04 (stat.)±0.07 (syst.)]× 10^−6, representing the most precise measurement to date and consistent with the theoretical prediction within one standard deviation. Additionally, we search for CP asymmetry in the J/ψ→μ^+μ^-μ^+μ^- decay and determine the T-odd observable to be A_T = [0.05± 0.04 (stat.)±0.01 (syst.)], which is consistent with CP conservation. In the search for J/ψ→ Z^′μ^+μ^- via Z^′→μ^+μ^-, no significant Z^′ signal is observed in the μ^+μ^- invariant mass region of $(0.212,~2.6)GeV/c^2$, and we set upper limits on the U(1)_L_μ−L_τ model coupling constant g^′ ranging from 0.001 to 0.294 at the 90\% confidence level, which is comparable to the upper limits set by Belle II for Z^′ masses below $0.7GeV/c^2$.
ER  -