pi(0) Photo- and electroproduction at threshold within a dynamical model

We show that, within a meson-exchange dynamical model describing most of th e existing pion electromagnetic production data up to the second resonance region, one is also able to obtain a good agreement with the pi (0) photo- and electroproduction data near threshold. The potentials used in the model are derived from an effective chiral Lagrangian. The only sizable discrepa ncy between our results and the data is in the P-wave amplitude P-3 = 2M(1) + M1- where our prediction underestimate the data by about 20%. In the ca se of pi (0) production, the effects of final state interaction in the thre shold region are nearly saturated by single charge exchange rescattering. T his indicates that in ChPT it might be sufficient to carry out the calculat ion just up to one-loop diagrams for threshold neutral pion production. (C) 2001 Elsevier Science B.V. All rights reserved.