Estimations of High-Energy Photopion Production at 0°

Experimental measurements indicate a much higher cross section than one-pion-exchange (OPE) predictions for high-energy charged-pion photoproduction at very small angles. Some possible mechanisms for 0° high-energy pion photoproduction are examined. It is shown that double pion photoproduction via a Reggeized $\rho$-exchange process may yield a considerable cross section at ${\theta }_{\pi }=0\mathrm{}°$. The parameters of the $\rho$ trajectory are determined and compared with other calculations. Since the residue of the $\rho$ trajectory is unknown, an experiment in a deuterium bubble chamber is suggested. The results are applied also to higher photon energies.