Glueball nature of the σ/f0(600) from ππ and γγ scatterings

We estimate the I=0 scalar meson σ/f0(600) parameters from ππ and γγ scattering data below 700 MeV using an improved analytic K-matrix model. A fit of the hadronic data gives a complex pole mass Mσ=422−i290MeV, while simultaneous best fits of the γγ→π+π−,π0π0 data give 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” γγ and the large hadronic widths at the “on-shell” mass are compatible with QCD spectral sum rules (QSSR) and some low-energy theorems (LET) expectations for an unmixed lowest mass glueball/gluonium σB of a mass around 1 GeV and a large OZI-violation decay into ππ.