The $Z_{cs}(3985)^-$ structure in a coupled-channels model

TL;DR

This paper analyzes the $Z_{cs}(3985)^-$ structure using a coupled-channels model, revealing its nature as a virtual state and predicting a new partner, aligning well with experimental data.

Contribution

It introduces a coupled-channels analysis constrained by previous models to explain the $Z_{cs}(3985)^-$ and predicts a new $Z_{cs}(4110)^\pm$ state, enhancing understanding of exotic hadron structures.

Findings

The $Z_{cs}(3985)^-$ is a virtual state below certain thresholds.

A new $Z_{cs}(4110)^\pm$ state is predicted as a flavor partner.

Model results agree with experimental spectra without fine tuning.

Abstract

The discovery of the $Z_c(3900)^\pm$ and $Z_b(10610)^\pm$ structures in the heavy quarkonium spectrum showed the need to incorporate hadron structures beyond the naive $qqq$ and $q\bar q$ systems in quark models. The new charged structure called $Z_{cs}(3985)^-$, spotted in the $K^+$ recoil-mass spectrum close to the $D^-_s D^{*0}/D^{*-}_sD^0$ threshold, is a new evidence in this line. In this work, we analyze the $Z_{cs}(3985)^-$ state, following the calculation of the $Z_c$ and $Z_b$ states using a chiral constituent quark model in a coupled-channels calculation, with all the parameters constrained from previous calculations. The pole structure of the S-matrix shows two virtual poles below the $D_s^-D^{*\,0}$ and $D_s^{*\,-}D^{*\,0}$ thresholds compatible with the $Z_{cs}(3985)^\pm$ and a new predicted $Z_{cs}(4110)^\pm$ structure, the SU(3) flavor partner of the $Z_c(4020)^\pm$. The $K^+$ recoil-mass spectrum is calculated in good agreement with LHCb and BESIII experimental data, with no fine tuning of the model parameters. Our results indicate that the $Z_{cs}(3985)^\pm$ and $Z_{cs}(4000)^\pm$ signals originate from the same virtual state.