Publication

Observation of a Threshold Enhancement in the π+π- Spectrum in ψ (3686) →π+π-J/ψ Decays

Jianxin Zhang
2026

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 resonancelike 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 MeV/c2 and a width of 16.3±0.9 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.

Official source

https://infoscience.epfl.ch/entities/publication/b6c0af52-6984-42e9-ac34-87018eaf3713

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Jianxin Zhang
2026

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/b6c0af52-6984-42e9-ac34-87018eaf3713

About this result

Related concepts (32)

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Observation of a Threshold Enhancement in the π+π- Spectrum in ψ (3686) →π+π-J/ψ Decays

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