Electromagnetic form factors of the proton at low four-momentum transfer

Abstract

Electron-proton elastic scattering cross sections were measured at low four-momentum transfers squared ( q 2 from 0.13 to 2.15 fm −2) at six different energies between 150 and 275 MeV. The electric ( G E) and magnetic ( G M) form factors of the proton have been determined by Rosenbluth plots and independently by using analytical functions for the form factors to fit the cross sections. The electric form factor is found to deviate significantly from the dipole fit. From the slope of the form factor functions at q 2 = 0 the rms radii of the charge and the magnetic moment distribution were determined. The charge rms radius is found to be more than 10% larger than the value given by the dipole fit.