Systematics of quark-antiquark states and scalar exotic mesons

The analysis of the experimental data of Crystal Barrel Collaboration on the p anti-p annihilation in flight with the production of mesons in the final state resulted in a discovery of a large number of mesons over the region 1900-2400 MeV, thus allowing us to systematize quark-antiquark states in the (n,M^2) and (J,M^2) planes, where n and J are radial quantum number and spin of the meson with the mass M. The data point to meson trajectories in these planes being approximately linear, with a universal slope. The sector of scalar mesons is discussed in more detail, where, on the basis of the recent K-matrix analysis, the nonet classification of quark-antiquark states was performed: in the region below 2000 MeV, two scalar nonets are fixed, that is, the basic one and the nonet of the first radial excitation. In the scalar sector, there are two states with the isospin I=0, which are extra ones with respect to the quark--antiquark classification, i.e. exotic states: the broad resonance f0(1200-1600) and the light sigma-meson. The ratios of coupling constants for hadronic decays to the states pi pi, K anti-K, eta eta, eta eta' point to the gluonium nature of the broad state f0(1200-1600).