First observation of the electromagnetic Dalitz decay ψ(3686) → μ⁺ μ^- η^′

@misc{collaboration2026first,
  title = {{First observation of the electromagnetic Dalitz decay $ψ(3686) \rightarrow μ^+ μ^- η^\prime$}},
  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 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 X. K. Cai 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},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.07054},
  eprint = {2610.07054},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.07054},
}

TY  - UNPB
TI  - First observation of the electromagnetic Dalitz decay ψ(3686) → μ^+ μ^- η^′
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  - 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  - X. K. Cai
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
PY  - 2026
DA  - 2026/10/05
PB  - arXiv
DO  - 10.48550/arxiv.2610.07054
UR  - https://arxiv.org/abs/2610.07054
AB  - Utilizing (2712.4 ± 14.3)×10^6 ψ(3686) events collected by the BESIII detector at the symmetric e^+ e^- collider BEPCII, we report the first observation of the electromagnetic Dalitz decay $ψ(3686) \to μ^+ μ^-η^{\prime} $ with a statistical significance of 6.1σ. The branching fraction is determined to be ℬ(ψ(3686) → μ^+ μ^- η^′)=(4.1 ± 1.0_stat. ± 0.4_syst.)× 10^−7. The ratio to the branching fraction of the radiative decay ψ(3686) → γη^′ is estimated to be (3.3±0.9)×10^−3, which is consistent with the prediction of the vector meson dominance model within 1σ. Furthermore, using the branching fraction of ψ(3686) → e^+ e^- η^′ previously measured by the BESIII experiment, the ratio between the muon and the electron channels is evaluated to be 0.22±0.07, which is consistent with the calculation of the vector meson dominance model within 1σ, and no significant violation of lepton flavor universality is found.
ER  -