Small-Angle Photoproduction and Conspiracy

Abstract

In any reaction of the class $\pi +B\to V+B$, or $V+B\to \pi +B$, nonconspiring amplitudes with a meson helicity change ($h_V-h_{\pi }\ne 0$) 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.