Determination of the pion form factor up toQ2=4GeV2from single-charged-pion electroproduction

We report new measurements of the electroproduction of single charged pions from both hydrogen and deuterium targets carried out at the Wilson Synchrotron Laboratory at Cornell University. Measurements were made at the ($W,Q^2$) points (2.15 GeV, 1.2 ${\mathrm{GeV}}^2$), (2.15, 4.0), and (3.11, 1.2) with hydrogen and deuterium and at (2.15, 2.0), (2.67, 3.4), and (3.11, 1.7) with only hydrogen. The deuterium data were used to determine the ratio of the cross sections for the reactions ${\gamma }_{V}d\to {\pi }^{+}n{n}_s$ and ${\gamma }_{V}d\to {\pi }^{-}p{p}_s$ and thus to measure the isoscalar contribution to the reaction ${\gamma }_{V}p\to {\pi }^{+}n$. The data are consistent with the hypothesis that this ratio is a universal function of the momentum transfer. The measured ratio was used to determine from the hydrogen data and the data taken in earlier experiments the isovector component of the cross section. The dispersion theory formulated by Berends was then used to determine from the isovector component the pion form factor in the $Q^2$ range from 0.2 to 4.0 ${\mathrm{GeV}}^2$. A simple pole expression of the form ${[1+\frac{Q^2}{(0.471\mathrm{}\pm 0.010)}]}^{-1\mathrm{}}$ gives a good fit to the data.