The Electric Dipole Amplitudes of the Neutral Pion Photoproduction on the Proton near Threshold

The electric dipole amplitude E 0+ for p (γ, π 0 ) p near threshold has been extracted from the experimental data by fitting the total cross section in high energy region, E γ >160 MeV. The result is (-1.56±0.10)×10 -3 m π+ -1 . This amplitude is calculated by taking the vector mesons into account in the pole model of t-channel. Our analysis manifests a favor of negative sign for the ρπγ coupling constant.