Zeros in energy and angular distributions with real or virtual photons

We consider $\gamma q_i\to W^{\pm }{q}_j$ and its crossed channels to show how kinematics and quarkcharge assignment together determine the occurrence of a zero in the amplitude. Then we calculate the amplitude with off-mass-shell photons which we use first to show how $W^{\pm }\to q_i{\overline{q}}_j{e}^{+}{e}^{-}$, $q_i{\overline{q}}_j\to W^{\pm }{e}^{+}{e}^{-}$, and $e^{\pm }{q}_i\to e^{\pm }{W}^{\pm }{q}_j$ can explore the region around the zeros, and second to point out that the photon reaction may be unique for observing these zeros.