In light of recent high-precision data taken by the BESIII Collaboration, we reconsider the dipion transition 𝜓(3686) →𝐽/𝜓𝜋+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.
Chen et al. (Thu,) studied this question.