The newly observed $ Z_{cs}(3985)^- $ state: in vacuum and a dense medium

We report on some properties of the newly observed charged hidden-charmed open strange $Z_{cs}(3985)^-$ state by BESIII Collaboration. Assigning the quantum numbers $J^{P} = 1^{+}$ and the quark composition $c \bar c s\bar u$ and considering it as the strange partner of the famous $Z_c(3900)$ state, we estimate the mass of the $Z_{cs}(3985)^-$ resonance in vacuum and compare it with the experimental data. We also investigate its mass, current coupling and vector-self energy in a medium with finite density. Our result on the mass in vacuum agrees well with the experimental data. We estimate the mass and current coupling of the b-partner of this state, $Z_{bs}$, in the vacuum as well. For its mass we get $m_{Z_{bs}}= 10732^{+97}_{-46}~\mbox{MeV}$, which may be checked via other nonperturbative approaches as well as future experiments. We present the dependence of the spectroscopic parameters of $Z_{cs}(3985)^-$ state on density and observe that these parameters are linearly changed with increasing in the density.