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Why is the Zc(3900) absent in the hcπ final state?

Quanxing Ye1,2,3, Ying Zhang1,2,3,*, Peng-Yu Niu1,3,†, and Qian Wang1,3,4,5,‡

  • 1State Key Laboratory of Nuclear Physics and Technology, Institute of Quantum Matter, South China Normal University, Guangzhou 510006, China
  • 2Key Laboratory of Atomic and Subatomic Structure and Quantum Control (MOE), Guangdong-Hong Kong Joint Laboratory of Quantum Matter, Guangzhou 510006, China
  • 3Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter, Guangdong Provincial Key Laboratory of Nuclear Science, Guangzhou 510006, China
  • 4Southern Center for Nuclear-Science Theory (SCNT), Institute of Modern Physics, Chinese Academy of Sciences, Huizhou 516000, Guangdong Province, China
  • 5Research Center for Nuclear Physics (RCNP), Osaka University, Ibaraki 567-0047, Japan

  • *These authors contributed equally to this work.
  • †Contact author: niupy@m.scnu.edu.cn
  • ‡Contact author: qianwang@m.scnu.edu.cn
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Phys. Rev. D 113, 114017 – Published 9 June, 2026

DOI: https://doi.org/10.1103/lstf-r8nc

Abstract

In this work, we perform a comprehensive phenomenological analysis of the exotic hadronic states Zc(3900), Zc(4020), Zb(10610), and Zb(10650) within the framework of heavy quark spin symmetry (HQSS) and its violation. By constructing S-wave contact interactions between elastic (DD¯*/D*D¯* or BB¯*/B*B¯*) and inelastic (J/ψπ,hcπ or ϒπ, hbπ) channels, we solve the Lippmann-Schwinger equation to obtain physical production amplitudes and perform a global fit to experimental invariant-mass spectra. Our results demonstrate a striking difference between the charm and bottom sectors: HQSS violation is negligible in the bottom system, leading to comparable peak structures for both Zb states in all hidden-bottom decay channels. In contrast, significant HQSS breaking is required to describe the Zc system, where the violation is predominantly concentrated in the elastic interactions. This explains the observed selectivity: Zc(3900) appears prominently only in J/ψπ, while Zc(4020) appears only in hcπ. Regardless of whether HQSS violation is taken into account, both the Zb(10610) and Zb(10650) poles can appear near the BB¯* and B*B¯* thresholds, respectively. In the hidden charm sector, however, only the framework that includes HQSS violation can successfully describe the experimental data, leading to a single pole around the DD¯* threshold, which is identified as the Zc(3900). Meanwhile, the structure associated with the Zc(4020) is interpreted as a cusp effect. The robustness of our model is verified against variations of the form factor and cutoff, showing stable results.

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Phys. Rev. D 113, 114017– Published 9 June, 2026
  • Received 12 January 2026
  • Accepted 7 May 2026
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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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