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

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 $D_s^{-}{D}^{\ast 0}\mathrm{/}{D}_s^{\ast -}{D}^0$ 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 $D_s^{-}{D}^{\ast 0}$ and $D_s^{\ast -}{D}^{\ast 0}$ 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.