ENERGY-DEPENDENCE OF THE FORM-FACTOR FOR ELASTIC ELECTRON-SCATTERING FROM C-12

A static analysis of measurements of C-12 elastic electron-scattering cross sections demonstrates unambiguously the existence of a form-factor energy dependence beyond that due to Coulomb distortion effects. This energy dependence increases smoothly as a function of momentum transfer and incident energy in the region covered by the experiments (1.0 < q(eff) < 2.3 fm-1, 240 < E0 < 690 MeV). Outside the first diffraction minimum the discrepancies between the form factors deduced from data obtained at different energies are as large as 5%; in the minimum discrepancies as large as 18% have been observed. Including dispersion corrections which are reasonably compatible with this observed energy dependence in the analysis of the data increases the rms charge radius deduced for C-12 by 0.007 to 2.478(9) fm, which is in excellent agreement with the value from muonic x-ray studies.