Small-Angle Photoproduction and Conspiracy

In any reaction of the class π+B→V+B, or V+B→π+B, nonconspiring amplitudes with a meson helicity change (hV-h_π≠0) exhibit a dip at small angles. Normally, this would simply mean that the zero-helicity-change amplitude dominates forward production. But in photoproduction, since the photon has no longitudinal component, there is no zero-helicity-change amplitude, and in the absence of conspiracy a forward dip will appear in the differential cross section. When conspiracy is present, the dip does not appear. Thus, forward photoproduction provides a good test for conspiracy.