Photoproduction Of Neutral Pions On Protons Near Threshold PDF Download

Neutral pion photoproduction on the nucleon near threshold is investigated using a dynamical model. It is shown that the commonly used procedure, based on an analytical continuation of the K-matrix to the unphysical region, is not compatible to a dynamical approach. We show that the final state interaction (FSI) amplitude derived from a dynamical model could involve large cancellation between the different pion photoproduction mechanisms. This leads that the FSI due to the intermediate [pi]°p state can be as important as that due to the [pi]n intermediate state. At threshold, we obtain E{sub 0+} = -1.92 × 10−3/m{sub {pi}+}. This number is close to the measured value of E{sub 0+} = -1.5 × 10−3/m{sub {pi}+}. No violation of the low energy theorem is required to obtain good agreement between the calculated total cross sections and experimental data drum threshold to about 400 MeV incident photon energy. 10 refs., 4 figs., 3 tabs.