Theoretical study of the γγ→meson-meson reaction

We present a unified theoretical picture which studies simultaneously the gamma gamma --> pi(+)pi(-), pi(0) pi(0), K+K-, K-0 (K) over bar(0), pi(0) eta reactions up to about root s = 1.4 GeV reproducing the experimental cross sections. The present work implements in an accurate way the final state interaction 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 f(0), a(0), 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 f(2)(1270) and a(2)(1370) resonances. We also evaluate the decay width of the f(0)(980) and a(0)(980) resonances into the gamma gamma channel. (C) 1998 Elsevier Science B.V.