Nucleon Electromagnetic Form Factors and Densities

摘要

We review data for nucleon electromagnetic form factors, emphasizing recent measurements of G_E/G_M that use recoil or target polarization to minimize systematic errors and model dependence. The data are parametrized in terms of densities that are consistent with the Lorentz contraction of the Breit frame and with pQCD. The dramatic linear decrease in G_(Ep)/G_(Mp)for 1 ≤ Q~2 ≤ 6 (GeV/c)~2 demonstrates that the charge is broader than the magnetization of the proton. High-precision recoil polarization measurements of G_(En) show clearly the positive core and negative surface charge of the neutron. Combining these measurements, we display spatial densities for u and d quarks in nucleons.