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  • Letter
  • Open Access

Deciphering the nature of X(2300) with the PACIAE model

Jian Cao1, Wen-Chao Zhang1,*, Jin-Peng Zhang1, Bo Feng1, An-Ke Lei2, Zhi-Lei She3, Hua Zheng1, Dai-Mei Zhou4,†, Yu-Liang Yan5 et al.

Ben-Hao Sa5,4,‡

  • *Contact author: wenchao.zhang@snnu.edu.cn
  • †Contact author: zhoudm@mail.ccnu.edu.cn
  • ‡Contact author: sabhliuym35@qq.com
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Phys. Rev. D 113, L031501 – Published 11 February, 2026

DOI: https://doi.org/10.1103/8d96-2tbq

Abstract

Inspired by the BESIII newest observation of an axial-vector particle X(2300) in the ψ(3686)→ϕηη′ process [M. Ablikim et al. (BESIII Collaboration), Phys. Rev. Lett. 134, 191901 (2025)], we simulate its production in e+e− collisions at s=4.95  GeV using the parton and hadron cascade model PACIAE 4.0. In this model, the final partonic state (FPS) and the final hadronic state (FHS) are simulated and recorded sequentially. While previous interpretations have described the X(2300) as an excited strangeonium state or an sss¯s¯ tetraquark state, it is noted that the U(1) anomaly coupling permits nonstrange quarks to couple to a vector ss¯ component via soft-gluon interactions. This motivates us to propose, for the first time, that the X(2300) could also be a qq¯ss¯ (q=u/d) state. Furthermore, we suggest another novel possibility that the X(2300) may be a hadro-strangeonium state, i.e., a bound system of a strangeonium and a light hadron. The excited strangeonium candidate is formed by coalescing an ss¯ quark pair in the FPS with the quantum statistical mechanics inspired dynamically constrained phase-space coalescence (DCPC) model. The tetraquark candidates of qq¯ss¯ and sss¯s¯ are similarly produced by coalescing four constituent quarks in the FPS. In contrast, a hadro-strangeonium candidate emerges from the recombination of the constituent mesons ϕ and η′/η in the FHS. We then calculate the X(2300)’s orbital angular momentum quantum number in its rest frame and perform the spectral classification for each of the above candidates. Given its quantum numbers JPC=1+−, the X(2300) is identified as a P-wave ss¯, an S-wave qq¯ss¯/sss¯s¯ or an S-wave ϕη′/ϕη candidate. For the first time, we estimate the production rates for these configurations. The P-wave ss¯ and S-wave qq¯ss¯ states are produced at rates on the order of 10−5, whereas the S-wave sss¯s¯ and ϕη′/ϕη states appear at rates on the order of 10−6. Moreover, significant discrepancies are observed in the rapidity distributions and the transverse momentum spectra among the different candidates. These discrepancies could be served as valuable criteria for deciphering the nature of the X(2300).

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Phys. Rev. D 113, L031501– Published 11 February, 2026
  • Received 15 September 2025
  • Accepted 21 January 2026
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