K-matrix analysis of the (IJ^{PC}=00^{++})-wave in the mass region below   1900 MeV
  We present the results of the current analysis of the partial wave IJ^{PC}=00^{++} based on the available data for meson spectra (pi-pi, K\bar K, eta-eta, eta-eta', pi-pi-pi-pi). In the framework of the K-matrix approach, the analytical amplitude has been restored in the mass region 280 MeV< \sqrt s <1900 MeV. The following scalar-isoscalar states are seen: comparatively narrow resonances f_0(980), f_0(1300), f_0(1500), f_0(1750) and the broad state f_0(1200-1600). The positions of the amplitude poles (masses and total widths of the resonances) are determined as well as pole residues (partial widths to meson channels pi-pi, K\bar K, eta-eta, eta-eta', pi-pi-pi-pi). The fitted amplitude gives us the positions of the K-matrix poles (bare states) and the values of bare-state couplings to meson channels thus allowing the quark-antiquark nonet classification of bare states. On the basis of the obtained partial widths to the channels pi-pi, K\bar K, eta-eta, eta-eta', we estimate the quark/gluonium content of f_0(980), f_0(1300), f_0(1500), f_0(1750), f_0(1200-1600). For f_0(980), f_0(1300), f_0(1500) and f_0(1750), their partial widths testify the q\bar q origin of these mesons though being unable to provide precise evaluation of the possible admixture of the gluonium component in these resonances. The ratios of the decay coupling constants for the f_0(1200-1600) support the idea about gluonium nature of this broad state. 
V. V. Anisovich, A. V. Sarantsev