Abstract
We estimate the I=0 scalar meson sigma/f_0(600) parameters from pi-pi andgamma-gamma scattering data below 700 MeV using an improved analytic K-matrixmodel. A fit of the hadronic data gives a complex pole mass M_sigma= 422-i290MeV, while simultaneous best fits of the gamma-gamma to pi+pi-, pi0pi0 datagive a direct width of (0.13+-0.05)keV, a rescattering component of(2.7+-0.4)keV and a total (direct+rescattering) width of (3.9+-0.6)keV."Running" these results to the physical real axis, the small "direct"gamma-gamma and the large hadronic widths at the "on-shell" mass are compatiblewith QCD spectral sum rules (QSSR) and some low-energy theorems (LET)expectations for an unmixed lowest mass glueball/gluonium sigma_B of a massaround 1 GeV and a large OZI-violation decay into pi-pi.