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Register a new userExplanation of the newly obseaved $Z_{cs}^-(3985)$ as a $D_s^{(*)-}D^{(*)0}$ molecular state
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Inspired by the newly observed $Z_{cs}^-(3985)$ by BESIII collaboration, we study the structure of this particle in the picture of $D_s^{(*)-}D^{(*)0}$ molecular state. Firstly we systematically construct the Lagrangians which describing the interaction of charmed mesons, taking into account the chiral and hidden local symmetries. With the obtained effective potentials from the Lagrangians constructed, we solve the coupled channel Bethe-Salpeter equation with the on-shell approximation. On the third Reimann sheet, a pole position of around $3982.34-i0.53$ MeV is obtained, which can be associated to the $Z_{cs}^-(3985)$ and explained as a loose bound state of $D_s^*bar{D}^*$.
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We study the $Z_{cs}(3985)$ state recently observed by the BESIII Collaboration in the one-boson-exchange model, assuming that it is a $bar{D}_s^{(*)}D^{(*)}$ molecule, which has the quark content $cbar{c}sbar{q}$ with $q = u$, $d$. It is shown that the one-boson-exchange potential is too weak to generate dynamcally $bar{D}_s D$, $bar{D}^*_s D$, and $bar{D}_sD^*$ states, while for the case of $bar{D}^*_s D^*$, very loosely bound states are likely, with binding energies of the order of several MeV. We conclude that, the observed $Z_{cs}(3985)$ state, if confirmed by further experiments, cannot be a pure hadronic molecular state of $bar{D}_s D^*$ and $bar{D}_s^*D$ and could consist of large components of compact nature.
Very recently, the BESIII collaboration reported a charged hidden-charm structure with strangeness in the recoil mass of $K^+$ of a process $e^+e^-to D_s^{*-}D^0K^+$ or $D_s^{-}D^{*0}K^+$, which is named as $Z_{cs}(3985)^{-}$. The newly observed charged structure can be treated as a partner structure with strangeness of well-known $Z_{c}(3885)^{-}$ reported in a process $e^+e^-to D^{*-}D^0pi^+$. In this work, we propose a novel picture to understand the nature of $Z_{cs}(3985)$. By performing a combined analysis for the line shape of the recoil mass distribution of $K^+$ at five energy points $sqrt{s}=4.628, 4.641, 4.661, 4.681, 4.698$ GeV, we find that the $Z_{cs}(3985)$ can be explained as a reflection structure of charmed-strange meson $D_{s2}^{*}(2573)$, which is produced from the open-charm decay of $Y(4660)$ with a $D_s^*$ meson. Furthermore, we predicted the angular distribution of final state $D_s^{*-}$ in process $e^+e^-to D_s^{*-}D^0K^+$ based on our proposed reaction mechanism, which may be an essential criterion to test the non-resonant nature of $Z_{cs}(3985)$ further.
New data from BESIII and LHCb show the existence of resonances with strangeness filling multiplets of the broken SU(3)_f symmetry, with the pattern predicted by the quark model. This is the case of the newly discovered Z_{cs} (3985) and Z_{cs}(4003), which have a natural accommodation in the tetraquark picture, as shown in this note. The quasi-degeneracy between Z_{cs} (3985) and Z_{cs}(4003) reproduces, in the strange sector, the situation observed with X(3872) and Z_c(3900). This represents a significative score in favor of the tetraquark scheme.
The newly observed hidden-charm tetraquark state $Z_{cs}(3985)$, together with $Z_c(3900)$ and $X(4020)$, are studied in the combined theoretical framework of the effective range expansion, compositeness relation and the decay width saturation. The elastic effective-range-expansion approach leads to sensible results for the scattering lengths, effective ranges and the compositeness coefficients, $i.e.$, the probabilities to find the two-charm-meson molecule components in the tetraquark states. The coupled-channel formalism by including the $J/psipi$ and $Dbar{D}^*/bar{D}D^*$ to fulfill the constraints of the compositeness relation and the decay width, confirms the elastic effective-range-expansion results for the $Z_c(3900)$, by using the experimental inputs for the ratios of the decay widths between $Dbar{D}^*/bar{D}D^*$ and $J/psipi$. With the results from the elastic effective-range-expansion study as input for the compositeness, we generalize the discussions to the $Z_{cs}(3985)$ by including the $J/psi K^{-}$ and $D_s^{-}D^{*0}/D_s^{*-}D^{0}$, and predict the partial decay widths of the $J/psi K^{-}$. Similar calculations are also carried out for the $X(4020)$ by including the $h_cpi$ and $D^*bar{D}^*$, and the partial decay widths of the $h_cpi$ is predicted. Our results can provide useful guidelines for future experimental measurements.
The newly observed $Xi(1620)^0$ by the Belle Collaboration inspires our interest in performing a systematic study on the interaction of an anti-strange meson $(bar{K}^{(*)})$ with a strange or doubly strange ground octet baryon $mathcal{B}$ ($Lambda$, $Sigma$, and $Xi$), where the spin-orbit force and the recoil correction are considered in the adopted one-boson-exchange model. Our results indicate that $Xi(1620)^0$ can be explained as a $bar{K}Lambda$ molecular state with $I(J^P)=1/2(1/2^-)$ and the intermediate force from $sigma$ exchange plays an important role. Additionally, we also predict several other possible molecular candidates, i.e., the $bar{K}Sigma$ molecular state with $I(J^P)=1/2(1/2^-)$ and the triply strange $bar{K}Xi$ molecular state with $I(J^P)=0(1/2^-)$.
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