Eta, eta-prime photoproduction and electroproduction off nucleons

The photo- and electroproduction of eta, eta-prime mesons on nucleons are investigated within a relativistic chiral unitary approach based on coupled channels. The s-wave potentials for electroproduction and meson-baryon scattering are derived from a chiral effective Lagrangian which includes the eta-prime as an explicit degree of freedom and incorporates important features of the underlying QCD Lagrangian such as the axial U(1) anomaly. The effective potentials are iterated in a Bethe-Salpeter equation and cross sections for eta, eta-prime photo- and electroproduction from nucleons are obtained. The results for the eta-prime photoproduction cross section on protons reproduce the appearance of an S_{11} resonance around 1.9 GeV observed at ELSA. The inclusion of electromagnetic form factors increases the predicted eta electroproduction cross sections on the proton, providing a qualitative explanation for the hard form factor of the photocoupling amplitude observed at CLAS.