ar X iv : h ep - p h / 02 12 25 6 v 1 1 7 D ec 2 00 2 η , η ′ photo - and electroproduction off nucleons

The photo-and electroproduction of the η, η ′ 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 η ′ 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 η, η ′ photo-and electroproduction from nucleons are obtained. The results for the η ′ 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 η electroproduction cross sections on the proton, providing a qualitative explanation for the hard form factor of the photocoupling amplitude observed at CLAS.