p(γ,π0) cross section and the low energy theorem

The reported breakdown of the low energy theorem (LET) for p(γ,${\mathrm{\pi }}^0$) as deduced from recent measurements at Mainz and earlier at Saclay is reexamined and found to be premature. Both qualitative and quantitative arguments are presented that suggest the conventional LET disagrees with experiment at the 8–12 % level. There is, however, a strong quenching of ${\mathit{E}}_0^{+}$(${\mathrm{\pi }}^0$) near the ${\mathrm{\pi }}^{+}$ threshold which is described by a semiphenomenological rescattering calculation based on the integral equation for the transition operator. The results are in good agreement with the values of ${\mathit{E}}_0^{+}$(${\mathrm{\pi }}^0$) deduced from the Mainz experiment, as well as the differential cross sections. Comparisons are made with other data up to ${\mathit{E}}_{\gamma }$=300 MeV.