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Decoding the structure near the $π^{+} π^{-}$ mass threshold in $ψ (3686) \to J / ψ π^{+} π^{-}$ decays

Yun-Hua Chen ^1,*, Xiang-Kun Dong ^2,†, Feng-Kun Guo ^3,4,5,‡, Christoph Hanhart ^6,§, and Bastian Kubis ^2,∥

¹School of Mathematics and Physics, University of Science and Technology Beijing, Beijing 100083, China
²Helmholtz-Institut für Strahlen- und Kernphysik (Theorie) and Bethe Center for Theoretical Physics, Universität Bonn, 53115 Bonn, Germany
³Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190, China
⁴School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
⁵Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences, Huizhou 516000, China
⁶Institute for Advanced Simulation, Forschungszentrum Jülich, 52425 Jülich, Germany

^*Contact author: yhchen@ustb.edu.cn
^†Contact author: xiangkun@hiskp.uni-bonn.de
^‡Contact author: fkguo@itp.ac.cn
^§Contact author: c.hanhart@fz-juelich.de
^∥Contact author: kubis@hiskp.uni-bonn.de

Phys. Rev. D 113, 054018 – Published 12 March, 2026

DOI: https://doi.org/10.1103/r5lz-864p

Abstract

In light of recent high-precision data taken by the BESIII Collaboration, we reconsider the dipion transition $ψ (3686) \to J / ψ π^{+} π^{-}$ . 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 $Z_{c} (3900)$ state improves the fit quality only slightly.

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Strong interaction

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Phys. Rev. D 113, 054018– Published 12 March, 2026

Vol. 113, Iss. 5 — 1 March 2026

Received 3 December 2025
Accepted 23 February 2026

DOI: https://doi.org/10.1103/r5lz-864p

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

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Decoding the structure near the $π^{+} π^{-}$ mass threshold in $ψ (3686) \to J / ψ π^{+} π^{-}$ decays

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

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Decoding the structure near the $π^{+} π^{-}$ mass threshold in $ψ (3686) \to J / ψ π^{+} π^{-}$ decays