Probing the nature of Z_c states via the eta_c rho decay
  The nature of the so-called XYZ states is a long-standing problem. It has been suggested that such particles may be described as compact four-quark states or loosely bound meson molecules. In the present work we analyze the Z_c(') -> eta_c rho decay using both approaches. Such channel might provide useful insights on the nature of the Z_c('), helping discriminating between the two different models. 
A. Esposito, A.L. Guerrieri, A. Pilloni
hep-ph