Between November 1974, when the J/ψ particle was discovered, until 2003, when the X(3872) resonance was described by the Belle Collaboration, the quarkonium spectrum was satisfactorily described by naive quark models. However, the exploration of energies above the DD̄ threshold has led to the appearance of unexpected states, the so-called XYZ states, difficult to accommodate in the naive picture of a qq̄ bound states.
A common feature among all these exotic states is the presence of nearby two particle thresholds. This coincidence reinforces the intuition that the residual interaction between such two particles can form a molecular state. The description of this type of structures is very tricky from a theoretical point of view because the strength of the residual interaction is usually model dependent and one can generate spurious states if this interaction is not under control. In this talk we review the studies of meson-meson molecules performed in the University of Salamanca, using a constituent quark model that has been applied to a wide range of hadronic observables, and therefore all model parameters are completely constrained.
Zoom meeting ID：875 9780 4213