Two-photon width and gluonic component of sigma/f_0(600)

Abstract

We analyse data on pi pi and gamma gamma scattering below 700 MeV within an improved analytic K-matrix model. This model is based on an effective theory with couplings between resonances, hadrons and photons. The two-photon decay of a resonance can proceed through intermediate transition into charged hadrons (here: pi^+ pi^-) and their subsequent annihilation or through a ``direct'' transition into photons. Our analysis confirms the rather large total radiative width of the sigma/f_0(600) resonance which we find as (3.9 \pm 0.6) keV but suggests its dominance by the pi pi rescattering process. This process is not sensitive to the internal structure of the resonance contrary to the direct component which we find small, (0.13 \pm 0.05) keV, and well consistent with the expectations for an unmixed glueball according to the QCD sum rule calculations.

5 pages, 2 figures, Talk (W.O.) at the International Workshop on e+e- collisions from phi to psi, Frascati, April 2008, to appear in Nucl. Phys. B (Proc. suppl.)

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• Chiral Perturbation Theory, the $1/N_c$ expansion and Regge behaviour determine the structure of the lightest scalar meson
• Gluonium nature of the sigma/f_0(600) from its coupling to KK
• Light scalar mesons in QCD
• Observation of the Higgs Boson of strong interaction via Compton scattering by the nucleon