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

Inspired by the BESIII newest observation of an axial-vector particle X ( 2300 ) in the ψ ( 3686 ) → ϕ η η ′ process [M. Ablikim (BESIII Collaboration), ], 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 s s s ¯ s ¯ tetraquark state, it is noted that the U ( 1 ) anomaly coupling permits nonstrange quarks to couple to a vector s s ¯ component via soft-gluon interactions. This motivates us to propose, for the first time, that the X ( 2300 ) could also be a q q ¯ s s ¯ ( 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 s s ¯ quark pair in the FPS with the quantum statistical mechanics inspired dynamically constrained phase-space coalescence (DCPC) model. The tetraquark candidates of q q ¯ s s ¯ and s s s ¯ 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 J P C = 1 + − , the X ( 2300 ) is identified as a