What question did this study set out to answer?

To investigate the dipion transition in ψ(3686) → J/ψ π+π- decays using recent experimental data.

April 3, 2026Open Access

Decoding the structure near the π + π − mass threshold in ψ ( 3686 ) → J / ψ π + π − decays

Key Points

To investigate the dipion transition in ψ(3686) → J/ψ π+π- decays using recent experimental data.
Analyzed high-precision data from the BESIII Collaboration.
Applied dispersion theory to account for pion-pion interactions.
Examined the role of helicity-flip amplitudes in the invariant-mass distribution.
Substructure near the π+π- threshold is reproduced without requiring extra resonances.
Helicity-flip amplitudes significantly influence the dip in the invariant-mass distribution.
Virtual exchange of the charmoniumlike exotic Zc(3900) state yields a slight improvement in fit quality.

Abstract

In light of recent high-precision data taken by the BESIII Collaboration, we reconsider the dipion transition 𝜓⁡(3686) →𝐽/𝜓⁡𝜋+⁢𝜋−. The strong pion-pion final-state interactions are taken into account model independently by using dispersion theory. We find that we can reproduce the substructure near the 𝜋+⁢𝜋−threshold observed experimentally without introducing an extra resonance state. While a helicity-flip amplitude plays an important role for the formation of the dip in the invariant-mass distribution, the virtual exchange of the charmoniumlike exotic 𝑍𝑐⁡(3900)state improves the fit quality only slightly.

Decoding the structure near the π + π − mass threshold in ψ ( 3686 ) → J / ψ π + π − decays

Key Points

Abstract

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