Extraction of theπNNform factor from charged pion photoproduction

The $\pi \mathrm{NN}$ form factor $F_{\pi \mathrm{NN}}\mathrm{}\left(t\right)\mathrm{}$, at small values of the momentum transfer, $0<\mathrm{}\left|t\right|\mathrm{}\stackrel{\backsim }{<}0.3$ (${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$, has been determined from an analysis of the experimental data on $\gamma p\to {\pi }^{+}n$ for incident photon energies in the range 3.4-18 GeV. A total of 104 unpolarized differential cross sections and 22 asymmetries have been fitted with a Reggeized one-pion-exchange model. The best fits give for a monopole vertex function a range $\Lambda \approx 1000$ MeV and for a dual model type of form factor, an asymptotic rate parameter $\beta \approx 2.3-2.5$. These results are consistent with those of a recent analysis of $\mathrm{NN}$ charge exchange scattering data at high energy and the same range of momentum transfers. The contribution of non-one-pion exchanges to the photoproduction amplitudes has been found to be negligible and does not affect the ${\chi }^2$, thus leading to an essentially model independent extraction of $F_{\pi \mathrm{NN}}\mathrm{}\left(t\right)\mathrm{}$. The implications of these results for the construction of one-pion-exchange potentials in nuclear physics is briefly discussed.