Photoproduction ofπ±Δ(1236)from Hydrogen and Deuterium at 16 GeV

Cross sections for $\gamma p\to {\pi }^{-}{\Delta }^{++}$, $\gamma n\to {\pi }^{-}{\Delta }^{+}$, $\gamma p\to {\pi }^{+}{\Delta }^0$, and $\gamma n\to {\pi }^{+}{\Delta }^{-}$ have been measured at 16 GeV for momentum transfers $-t<~2$ Ge${\mathrm{V}}^2$. The charge-symmetric cross sections differ by typically a factor of 2, indicating interference between isoscalar and isovector photon amplitudes. The ratio of ${\pi }^{+}{\Delta }^0$ and ${\pi }^{+}{\Delta }^{-}$ cross sections is not consistent with pure isospin $I=1\mathrm{}$ exchange in the $t$ channel, appreciable $I=2\mathrm{}$ exchange being required. A factor-of-5 discrepancy is found for a vector-dominance plus line-reversal prediction.