The strange partner of the $Z_{c}$ structures in a coupled-channels model

TL;DR

This paper investigates the nature of the $Z_{cs}(3985)^-$ structure using a coupled-channels model, revealing it as a virtual state and predicting new related states, thus advancing understanding of exotic hadron structures.

Contribution

The study applies a coupled-channels chiral quark model to analyze the $Z_{cs}(3985)^-$, reproducing experimental spectra and predicting new states, including a flavor partner and hidden bottom strange states.

Findings

The $Z_{cs}(3985)^-$ is due to a virtual pole in the S-matrix.

Predicted a flavor partner of $Z_c(4020)$ at ~4110 MeV/$c^2$.

Forecasted new states in the hidden bottom strange sector.

Abstract

The discovery of a new charged structure in the $K^+$ recoil-mass spectrum near the $D^-_s D^{*0}/D^{*-}_sD^0$ threshold, dubbed $Z_{cs}(3985)^-$, reinforce the idea that the structure of hadrons goes beyond the naive $qqq$ and the $q\bar q$ structures. The existence of this state, with quark content $c\bar c s\bar u$, can be expected from the well-established $Z_c(3900)^\pm$ and $Z_c(4020)$ states using SU(3) flavor symmetry. The $Z_c$ structures have been explained using the chiral constituent quark model in a coupled-channels calculation and, in this work, we undertake the study of the $Z_{cs}(3985)^-$ using the same model. We are able to reproduce the $K^+$ recoil-mass spectrum without any fine tuning of the model parameters. The study of the analytical structure of the S-matrix allows us to conclude that the structure is due to the presence of one virtual pole. A second state, the SU(3) flavor partner of the $Z_c(4020)$ is predicted at $\sim\!\! 4110$ MeV/$c^2$. New states in the hidden bottom strange sector are also predicted.