UNIFIED APPROACH TO PSEUDOSCALAR MESON PHOTOPRODUCTIONS OFF NUCLEONS IN THE QUARK-MODEL

A unified approach to the pseudoscalar meson (pi, eta, and K) photopro ductions off nucleons are presented. It begins with the low energy QCD Lagrangian, and the resonances in the s and u channels are treated in the framework of thr quark modal. The duality hypothesis is imposed t o limit the number of the t-channel exchanges. The CGLN amplitudes for each reaction are evaluated, which include both proton and neutron ta rgets. The important role of the S-wave resonances in the second reson ance region is discussed, and is particularly important for the K, eta , and eta' photoproductions.