Observation of a Threshold Enhancement in the π⁰π⁰ Mass Spectrum in ψ(3686) → π⁰π⁰J/ψ Decays

@misc{collaboration2026observation,
  title = {{Observation of a Threshold Enhancement in the $π^0π^0$ Mass Spectrum in $ψ(3686) \rightarrow π^0π^0J/ψ$ Decays}},
  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.2610.13097},
  eprint = {2610.13097},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.13097},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Observation of a Threshold Enhancement in the π^0π^0 Mass Spectrum in ψ(3686) → π^0π^0J/ψ Decays
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  - 2026/10/09
PB  - arXiv
DO  - 10.48550/arxiv.2610.13097
UR  - https://arxiv.org/abs/2610.13097
AB  - Using a data sample of (2712.4±14.4)× 10^6 ψ(3686) events collected with the BESIII detector, we report a high-precision study of the π^0π^0 mass spectrum from ψ(3686)→π^0π^0J/ψ decays. The enhancement previously observed near the ππ mass threshold in the π^+π^- channel is confirmed, with a statistical significance exceeding 10σ. A fit with a Breit-Wigner function yields a mass of M = 274.3± 2.1_stat.±0.6_syst. MeV/c^2 and a width of Γ= 17.1± 1.5_stat.±0.5_syst. MeV, consistent with those from the π^+π^− channel. By including final-state interactions, we analyze the data using both chiral perturbation theory (ChPT) and QCD multipole expansion (QCDME). While the ChPT model describes the higher-mass region above 0.3 GeV/c^2 well, it fails to reproduce the significant threshold enhancement. In contrast, the QCDME model, which incorporates the S- and D-wave admixture structure of ψ(3686), provides a better description of the full π^0π^0 mass spectrum.
ER  -