Scalar isovector resonance photoproduction through the final state meson–meson interactions

We construct the amplitudes of πη photoproduction taking into account the effects of the πη–KK interchannel coupling. The idea of our model is to describe the scalar isovectors as dynamically produced in the final state while the initial stage of the reaction being described in terms of meson exchanges. Meson loops which arise this way include not only pseudoscalars but also vector mesons. These amplitudes are used to calculate the S-wave cross-sections and mass distributions in the πη effective mass region corresponding to the scalar resonances a0(980) and a0(1450). The values we obtained for a0(980) are comparable with predictions of other models while the cross-section for a0(1450) is about an order of magnitude larger than prediction based on the quark model. We show that the amplitudes with loops containing vector mesons calculated in the on-shell approximation are not suppressed in contrast to amplitudes containing only pseudoscalar loops. We also estimate the cross-sections for the P- and D-waves in the πη channel.