Measurement of 14N( gamma, pi +)14C (g.s.) at 200 MeV: A test of the distorted-wave impulse approximation for charged-pion photoproduction below the Delta (1232) resonance.

Differential cross sections for $^{14}\mathrm{N}(\ensuremath{\gamma}, {\ensuremath{\pi}}^{+})^{14}\mathrm{C}(\mathrm{g}.\mathrm{s}.)$ (${0}^{+}$1) have been measured for an incident photon energy ${E}_{\ensuremath{\gamma}}=200$ MeV at laboratory angles of 45\ifmmode^\circ\else\textdegree\fi{}, 60\ifmmode^\circ\else\textdegree\fi{}, 75\ifmmode^\circ\else\textdegree\fi{}, 90\ifmmode^\circ\else\textdegree\fi{}, 120\ifmmode^\circ\else\textdegree\fi{}, and 140\ifmmode^\circ\else\textdegree\fi{}. Momentum-space distorted-wave-impulse-approximation calculations, using a complete treatment of a one-body pion-photoproduction operator, are found to be in excellent agreement with the experimental data. The effect of the momentum-dependent terms in the nuclear photoproduction operator is observed. The reaction is found to be sensitive to input nuclear structure elements not observable in the ($e, {e}^{\ensuremath{'}}$) form-factor data.