Angular Distribution of Positive Pion Photoproduction from Hydrogen

The analysis of all available data on the angular distribution of positive pions in photoproduction is carried out using a recently suggested method. The results are then compared with various theoretical predictions. It is shown that below resonance the various forms of the nonrelativistic theory give similar enough predictions so that present experiments could not distinguish among them. Above resonance the predictions diverge, and both the Low theory and the dispersional approach give surprisingly good agreement with data even at energies as high as 470 Mev. Below resonance the agreement with experimental data seems to be questionable, but more precise experiments are needed before definite conclusions can be drawn. It is also shown that the backward-to-forward ratio of the differential cross section is sensitive to the contribution of the $P_{\frac{3}{2}}$, electric quadrupole state, and thus this ratio might become a good way of exploring the degree of enhancement of the electric quadrupole contribution.