Dynamical study of hidden-strange pentaquarks as analogs of the hidden-charm states

Motivated by the recent BESIII experiment~\cite{BESIII:2024muk} searching for hidden-strange exotic hadrons, we perform a systematic theoretical study of the hidden-strange pentaquark system within the framework of the quark delocalization color screening model (QDCSM) and the resonating group method (RGM). Our results demonstrate that the channel coupling effect plays a decisive role in the formation of bound and resonance states. It not only significantly enhances the short-range attraction but also induces essential attractive contributions from pion exchange. We predict three bound states with masses of $1759$ MeV, $2000$ MeV, and $2407$ MeV. Furthermore, we report the existence of a hidden-strange pentaquark resonance state, $ΞK^{\ast}$, with quantum numbers $I(J^{P})=0(1/2^{-})$. This resonance is identified in the $S$-wave scattering phase shifts of the $Λη_{s}$ and $Λϕ$ open channels, with a predicted mass in the range of $2204\text{–}2208$ MeV. By accounting for both the scattering width from channel coupling and the intrinsic decay width of the constituent $K^{\ast}$, the total decay width is estimated to be $55\text{–}63$ MeV. These theoretical predictions provide important guidance for future experimental searches for such exotic states at facilities like BESIII.

💡 Research Summary

In this work the authors perform a comprehensive dynamical investigation of hidden‑strange pentaquark systems (with quark content nn s s \bar{s}) using the quark delocalization color screening model (QDCSM) together with the resonating group method (RGM). The QDCSM extends the traditional non‑relativistic quark‑cluster approach by allowing quark wave functions to delocalize between two color‑neutral clusters (a three‑quark baryon and a quark‑antiquark meson) and by introducing a phenomenological color‑screening factor μ_ij that reduces the effective confinement interaction when quarks belong to different clusters. The model parameters (confinement strength a_c, screening parameters μ_nn, μ_ns, μ_ss, and the strong coupling α_s) are fixed by reproducing the spectra of ordinary mesons and baryons as well as nucleon‑nucleon, nucleon‑hyperon, and hyperon‑hyperon scattering phase shifts.

The authors enumerate all S‑wave channels with isospin I = 0, 1 and spin‑parity J^P = 1/2⁻, 3/2⁻, 5/2⁻ that can couple to the hidden‑strange pentaquark configuration. These include Λη′, Λφ, Ση′, Σφ, ΞK, ΞK*, Ξ* K*, etc. For each channel they compute an effective inter‑cluster potential V(S) = E(S) – E(∞) by evaluating the expectation value of the full Hamiltonian with the RGM wave function at a given separation S between the two clusters. The potentials reveal that the I = 0, J^P = 1/2⁻ sector is the most attractive, largely due to the combined effect of short‑range color‑screened confinement, one‑gluon exchange, and especially the medium‑range pion‑exchange contribution that becomes operative when channel coupling is allowed.

Bound‑state calculations are carried out first in a single‑channel approximation and then with full coupled‑channel dynamics. In the single‑channel case only weakly bound or unbound solutions appear. However, when the relevant open channels are coupled, three bound states emerge:

• a state at 1759 MeV dominated by the Λη′ configuration,
• a state at 2000 MeV dominated by Λφ,
• a state at 2407 MeV dominated by the ΞK* configuration.

These bound states owe their existence to the enhanced short‑range attraction from color screening and the additional attraction supplied by pion exchange when the channels are mixed.

To search for resonances the authors analyze S‑wave scattering phase shifts for the coupled channels. In the I = 0, J^P = 1/2⁻ sector a clear rapid rise of the phase shift is observed around 2204–2208 MeV in the Λη_s and Λφ coupled system, signalling a resonance that can be identified as a hidden‑strange pentaquark with the dominant component ΞK*. The resonance mass is predicted to lie in the 2204–2208 MeV interval. Its total width is estimated by adding the scattering width generated by channel coupling (≈25–30 MeV) to the intrinsic decay width of the constituent K* meson (≈30–35 MeV), yielding a combined width of 55–63 MeV.

The paper emphasizes that the channel‑coupling effect is decisive: it not only strengthens the short‑range attraction but also activates pion‑exchange contributions that are otherwise absent in isolated channels. This mechanism mirrors the situation in the hidden‑charm sector, where many of the observed Pc and Pc s states are interpreted as hadronic molecules near open‑charm thresholds.

Finally, the authors discuss the experimental implications. The predicted bound states and the ΞK* resonance should be accessible in processes where hidden‑strange pentaquarks can be formed, such as ψ(3686) → Σ⁰ \bar{Σ}⁰ φ decays studied by BESIII, or in future measurements at PANDA and other facilities capable of producing strange baryon–meson final states. Observation of the Λη_s, Λφ, or ΞK* invariant‑mass spectra with the quoted masses and widths would provide a stringent test of the QDCSM framework and of the importance of channel coupling in multiquark dynamics.

In summary, the study predicts three hidden‑strange pentaquark bound states (1759, 2000, 2407 MeV) and one resonance (ΞK*, I = 0, J^P = 1/2⁻) with mass ≈ 2205 MeV and width ≈ 60 MeV, highlighting the crucial role of channel coupling and pion exchange in generating attraction. These results offer concrete targets for upcoming experimental searches and deepen our understanding of exotic hadron spectroscopy beyond the hidden‑charm sector.