Femtoscopy can tell whether Z_c(3900) and Z_cs(3985) are resonances, virtual states, or bound states

There have been extended and heated discussions on the nature of the two exotic states, Z_c(3900) and Z_cs(3985), particularly whether they are near-threshold resonances, virtual states, or bound states. In this work, we demonstrate for the first time that the femtoscopic technique can be employed to distinguish between these three scenarios. More concretely, based on the Koonin-Pratt formula with a Gaussian source, we show that the low-momentum D⁰D^*-/D⁰D_s^*- correlation functions significantly differ in the three scenarios. The high-momentum results exhibit distinct characteristics in the resonant and virtual state scenarios, especially in small collision systems of 1 fm, as produced in pp collisions at the LHC. We hope that these discoveries will stimulate further experimental studies and help clarify the nature of the many exotic states that have been discovered.