Theoretical Study of the γγ-->meson-meson Reaction (HADRON'97)

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We present a unified picture which studies simultaneously the gamma gamma--> pi+ pi-, pi⁰ pi⁰,K+ K-, K⁰ barK⁰, pi⁰ eta reactions up to about sqrt(s)=1.4 GeV reproducing the experimental cross sections. The present work implements in an accurate way the final state interactions of the meson-meson system, which is shown to be essential in order to reproduce the data, particularly the L=0 channel. This latter channel is treated here following a recent theoretical work in which the meson-meson amplitudes are well reproduced and the f₀, a₀, sigma resonances show up clearly as poles of the t matrix. The present work, as done in earlier ones, also incorporates elements of chiral symmetry and exchange of vector and axial resonances in the crossed channels, as well as a direct coupling to the f₂(1270) and a₂(1320) resonances. We also evaluate the decay width of the f₀(980) and a₀(980) resonances into the gamma-gamma channel.