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arXiv · 2512.01679

Decoding the structure near the $\pi^+\pi^-$ mass threshold in $\psi(3686) \rightarrow J/\psi \pi^+\pi^-$ decays

Yun-Hua Chen·Xiang-Kun Dong·Feng-Kun Guo·Christoph Hanhart·Bastian Kubis
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Abstract

In light of recent high-precision data taken by the BESIII Collaboration, we reconsider the dipion transition $\psi(3686) \rightarrow J/\psi \pi^+\pi^-$. 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 $\pi^+\pi^-$ 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 $Z_c(3900)$ state improves the fit quality only slightly.

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Yun-Hua Chen, Xiang-Kun Dong, Feng-Kun Guo, Christoph Hanhart, Bastian Kubis. 2025-12-01. Decoding the structure near the $\pi^+\pi^-$ mass threshold in $\psi(3686) \rightarrow J/\psi \pi^+\pi^-$ decays. https://doi.org/10.1103/r5lz-864p

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