Unified description of the hidden-charm tetraquark states Zcs(3985), Zc(3900), and X(4020)

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/psi pi and D (D) over bar*/(D) over barD* 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 D (D) over bar*/(D) over barD* and J/psi pi. 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-D)-D-s*(0)/D*D--(s)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(c)pi and D*(D) over bar*, and the partial decay widths of the h(c)pi is predicted. Our results can provide useful guidelines for future experimental measurements.

Automated summary

In this study, the newly observed hidden-charm tetraquark state Z(cs)(3985), together with Z(c)(3900) and X(4020), are investigated using a combined theoretical framework. Results from elastic effective-range-expansion method and coupled-channel formalism provide insights into the properties of these exotic states and predictions for their decay widths.