High-Energy Photoproduction of Nonresonantπ+π−Pairs and the Dipion Final-State Interaction

Working with nuclei as targets, a theory is presented for the high-energy photoproduction of nonresonant ${\pi }^{+}{\pi }^{-}$ pairs which takes into account the scattering of both pions from the nucleus. Our amplitudes turn out to be significantly smaller than those calculated using the conventional Drell-Söding theory of this process, which allows for the scattering of only one pion. We then take into account the fact that these pion pairs can resonate in the final state and form a ${\rho }^0$ meson "anomalously." Both of these effects are relevant to the analysis of the reaction $\gamma +A\to {\pi }^{+}+{\pi }^{-}+A$ and "anomalous" ${\rho }^0$ photoproduction should prove relevant, as well, to understanding the reaction $\gamma +A\to l^{+}+l^{-}+A$.