Electromagnetic Form Factors of the Proton

Abstract

This paper reports experimental findings on the Dirac (${F}_{1}$) and Pauli (${F}_{2}$) form factors of the proton. The form factors have been obtained by using the Rosenbluth formula and the method of intersecting ellipses in analyzing the elastic electron-proton scattering cross sections. A range of energies covering the interval 200-1000 Mev for the incident electrons is explored. Scattering angles vary from 35\ifmmode^\circ\else\textdegree\fi{} to 145\ifmmode^\circ\else\textdegree\fi{}. Values as high as ${q}^{2}\ensuremath{\cong}31$ ${\mathrm{f}}^{\ensuremath{-}2}$ ($q=\mathrm{e}\mathrm{n}\mathrm{e}\mathrm{r}\mathrm{g}\mathrm{y}\ensuremath{-}\mathrm{m}\mathrm{o}\mathrm{m}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{u}\mathrm{m}\phantom{\rule{0ex}{0ex}}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{n}\mathrm{s}\mathrm{f}\mathrm{e}\mathrm{r}$) are investigated, but form factors can be reliably determined only up to about ${q}^{2}=25$ ${\mathrm{f}}^{\ensuremath{-}2}$. Splitting of the form factors is confirmed. The newly measured data are in good agreement with earlier Stanford data on the form factors and also with the predictions of a recent theoretical model of the proton. Consistency in determining the values of the form factors at different energies and angles gives support to the techniques of quantum electrodynamics up to ${q}^{2}\ensuremath{\cong}25$ ${\mathrm{f}}^{\ensuremath{-}2}$. At the extreme conditions of this experiment (975 Mev, 145\ifmmode^\circ\else\textdegree\fi{}) the behavior of the form factors may be exhibiting some anomaly.