Molecular structures in the charmonium spectrum: the XYZ puzzle

We study in the framework of a constituent quark model the possible contributions of molecular structures to the XYZ charmonium-like states. We analyze simultaneously the structures and the possible molecular components in the coupled channel formalism. In the 1++ sector two states appear which could be identified with X(3872) and X(3940). The recently confirmed X(3915) state appears as a mixture of and components as a JPC = 0++ state in agreement with the new measurements. A second broad resonance which may correspond with the so-called Y(3940) state is found with these quantum numbers. In the JPC = 1−− sector we also found significant contributions of the molecular structures which may affect the phenomenology. In particular the study allows us to understand the G(3900) state recently observed in Belle and BaBar. All these resonances together with the prediction of the model of a structure for Z(3930) provide a reasonable scenario for the so-called XYZ states with masses near 3.9 GeV.