Observation of a resonance-like structure near the π⁺π^- mass threshold in ψ(3686) → π⁺π^-J/ψ

2025/09/28 by BESIII Collaboration, Ablikim, M., Achasov, M. N. +677 · 1 citation
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex)

paper · doi:10.48550/arxiv.2509.23761

Abstract

Based on the (2712.4±14.4)× 10⁶ ψ(3686) events collected with the BESIII detector, we present a high-precision study of the π⁺π^- mass spectrum in ψ(3686)→π⁺π^-J/ψ decays. A clear resonance-like structure is observed near the π⁺π^- mass threshold for the first time. A fit with a Breit-Wigner function yields a mass of 285.6± 2.5~\rm MeV/c² and a width of 16.3± 0.9~\rm MeV with a statistical significance exceeding 10σ. To interpret the data, we incorporate final-state interactions (FSI) within two theoretical frameworks: chiral perturbation theory (ChPT) and QCD multipole expansion (QCDME). ChPT describes the spectrum above 0.3 GeV/c² but fails to reproduce the threshold enhancement. In contrast, the QCDME model, assuming the ψ(3686) is an admixture of S- and D-wave charmonium, reproduces the data well. The pronounced dip near 0.3 GeV/c² offers new insight into the interplay between chiral dynamics and low-energy QCD.

Cited by

• Low-energy scattering of the J/ψπ and J/ψK systems

Related

• Decoding the structure near the π⁺π^- mass threshold in ψ(3686) → J/ψπ⁺π^- decays
• Revealing di-pion correlations for the observed substructure near the π⁺π^- mass threshold in ψ(3686)→ J/ψπ⁺π^-
• An anlaysis on J/ψ→π⁰γ^* within resonance chiral theory
• Observation of ψ(3686)→ 3ϕ
• Study of ψ(3686)→ΛΛω