Interference Effects of the Retardation Term in Pion Photoproduction

Abstract

It is shown that the difference in behavior of the high-energy (>450 Mev c.m.) total photoproduction cross sections for ${\pi }^{+}$ and ${\pi }^0$ can be explained by the presence of the retardation term in the case of the ${\pi }^{+}$ production. The analogy with the behavior at the ($\frac{3}{2}, \frac{3}{2}$) resonance is noted. The discussion naturally provides an explanation for the difference in center-of-mass energies of the lower high-energy peak found in ${\pi }^{-}-p$ scattering and the corresponding peak in the ${\pi }^{+}$ photoproduction. It is felt that the discussion contributes some evidence for the resonance nature of the peaks.