Method of Analysis of Charged Pion Photoproduction

It is explained why the usual analysis of the angular distribution of charged pion photoproduction with the help of a quadratic expression of $cos\theta$ ($\theta$ being the meson emission angle) is physically meaningless. A substitute scheme is proposed in which the angular distribution in the center-of-mass system, multiplied by ${(1-\beta cos\theta )}^2$ ($\beta$ being the meson velocity), is analyzed by a quartic expression in $cos\theta$. Such an analysis is given for several theories commonly in use.