Experimental Investigation of Pion Electroproduction

Measurements of the total cross section for the processes $e+p\ensuremath{\rightarrow}{e}^{\ensuremath{'}}+n+{\ensuremath{\pi}}^{+}$ and $e+p\ensuremath{\rightarrow}{e}^{\ensuremath{'}}+p+{\ensuremath{\pi}}^{0}$ are reported for a wide range of center-of-mass energies and momentum transfers extending above the first pion-nucleon resonance and to momentum transfers of 20 ${\mathrm{F}}^{\ensuremath{-}2}$. Only the final electron is observed in this experiment.Results are analyzed in terms of nucleon form factors using experimental pion-nucleon phase shifts and the theory of Fubini, Nambu, and Wataghin. In general, the data seem consistent with current picture of nucleon structure, except for a preference for a negative rather than positive neutron-electric form factor, ${G}_{\mathrm{En}}$. It is demonstrated from the electron angular distribution for constant momentum transfer and constant center-of-mass energy that pion electroproduction does in fact occur primarily through transverse currents. The general form of the separation into transverse and scalar photons for inelastic or elastic electron scattering is discussed. In addition, an approximate formula for the background process of wide-angle bremsstrahlung is quoted which appears to be accurate to 1-2% over a very wide range of electron and photon energies when compared to a numerical computation by a digital computer.