Spectrum of Hidden-Charm, Open-Strange Exotics in the Dynamical Diquark Model

TL;DR

This paper extends the dynamical diquark model to include hidden-charm, open-strange exotic states, analyzing their mass splittings, flavor mixing, and potential exchange effects, and successfully fits certain pentaquark states.

Contribution

The work develops a unified dynamical diquark model for heavy-quark exotics with open strangeness, incorporating flavor mixing and exchange effects, and fits observed pentaquark states.

Findings

Large mass splitting indicates significant SU(3) flavor mixing.

Average mass differences probe flavor octet-singlet mixing.

Limited impact of $ ext{eta}$-like exchanges on states.

Abstract

The observation by BESIII and LHCb of states with hidden charm and open strangeness ($c\bar c q\bar s$) presents new opportunities for the development of a global model of heavy-quark exotics. Here we extend the dynamical diquark model to encompass such states, using the same values of Hamiltonian parameters previously obtained from the nonstrange and hidden-strange sectors. The large mass splitting between $Z_{cs}(4000)$ and $Z_{cs}(4220)$ suggests substantial SU(3)$_{\rm flavor}$ mixing between all $J^P \! = \! 1^+$ states, while their average mass compared to that of other sectors offers a direct probe of flavor octet-singlet mixing among exotics. We also explore the inclusion of $\eta$-like exchanges within the states, and find their effects to be quite limited. In addition, using the same diquark-mass parameters, we find $P_c(4312)$ and $P_{cs}(4459)$ to fit well as corresponding nonstrange and open-strange pentaquarks.