Photon-fusion reactions from the chiral Lagrangian with dynamical light vector mesons

Abstract

We study the reactions γγ→π 0 π 0, π + π −, $K^{0}\bar{K}^{0}$ , K + K −, ηη and π 0 η based on a chiral Lagrangian with dynamical light vector mesons as formulated within the hadrogenesis conjecture. At present our chiral Lagrangian contains five unknown parameters that are relevant for the photon-fusion reactions. They parameterize the strength of interaction terms involving two vector meson fields. These parameters are fitted to photon-fusion data γγ→π 0 π 0, π + π −,π 0 η and to the decay η→π 0 γγ. In order to derive gauge invariant reaction amplitudes in the resonance region constraints from maximal analyticity and exact coupled-channel unitarity are used. Our results are in good agreement with the existing experimental data from threshold up to about 0.9 GeV for the two-pion final states. The a 0 meson in the π 0 η channel is dynamically generated and an accurate reproduction of the γγ→π 0 η data is achieved up to 1.2 GeV. Based on our parameter sets we predict the γγ→ $K^{0}\bar{K}^{0}$ , K + K −, ηη cross sections.