High-Energy Photoproduction of Charged Pions at Backward Angles

Measurements on large-angle photoproduction of ${\pi }^{+}$ mesons from hydrogen have been made at the Stanford Linear Accelerator Center for photon energies between 5 and 15.5 GeV and $u$ values from +0.05 to -1.8 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. The measured cross section decreased with energy approximately as $k^{-3\mathrm{}}$, showing no shrinkage in this range of $u$ values. Furthermore, it had a smooth $u$ dependence with no sign of a dip at $u\simeq -0.15\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ as would be expected from nucleon exchange. ${\pi }^{-}{\Delta }^{++}$ production was measured at 5 GeV and shows a rapid decrease with increasing $\mathrm{}\left|u\right|\mathrm{}$.