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Register a new userThreshold effects as the origin of $Z_{cs}(4000)$, $Z_{cs}(4220)$ and $X(4700)$ observed in $B^+to J/psi phi K^+$
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We investigate the $B^+to J/psi phi K^+$ decay via various rescattering diagrams. Without introducing genuine exotic resonances, it is shown that the $Z_{cs}(4000)$, $Z_{cs}(4220)$ and $X(4700)$ reported by the LHCb collaboration can be simulated by the $J/psi K^{*+}$, $psi^prime K^+$ and $psi^prime phi$ threshold cusps, respectively. These cusps are enhanced by some nearby triangle singularities. The $X(4685)$ with $J^P=1^+$ cannot be well simulated by the threshold effects in our model, which implies that it may be a genuine resonance.
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The BESIII Collaboration has observed a candidate for a $c bar c s bar u$ tetraquark $Z_{cs}$ at $(3982.5^{+1.8}_{-2.6} pm 2.1)$ MeV and width $(12.8^{+5.3}_{-4.4} pm 3.0)$ MeV, while the LHCb Collaboration has observed a $Z_{cs}$ candidate in the $jpsi K^-$ channel with mass of $(4003 pm 6 ^{+4}_{-14})$ MeV and width $(131 pm 15 pm 26)$ MeV. In this note we examine the possibility that these two states are distinct eigenstates of a mixing process similar to that which gives rise to two axial-vector mesons labeled by the Particle Data Group $K_1(1270)$ and $K_1(1400)$. The main point is that on top of a $bar c c$ pair, the $Z_{cs}$ states have the same light quark content as the $K_1$-s. In the compact tetraquark picture this implies several additional states, analogous to members of the $K_1$ nonet. These states have not yet been observed, nor are they required in the molecular approach. Thus experimental discovery or exclusion of these extra states will be a critical test for competing models of exotic mesons with hidden charm.
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.
We investigate the production of the hidden-charm pentaquark $P_{cs}^0(4459)$ with strangeness in the $K^- p to J/psi Lambda$ reaction, employing two different theoretical frameworks, i.e., the effective Lagrangian method and the Regge approach. Having determined all relevant coupling constants, we are able to compute the total and differential cross sections for the $K^- p to J/psi Lambda$ reaction. We examine the contributions of $P_{cs}$ with different sets of spin-parity quantum number assigned. The present results may give a guide for possible future experiments.
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