Contribution plenary talk
Jefferson Lab’s Contribution to the Characterization of the Proton Form Factors (2017 Bonner prize)
Elastic scattering of electrons (or positrons) on the proton (or neutron) provide information on the charge and magnetization distributions inside the nucleon. Traditionally, following the pioneering work of Hofstadter in the mid-fifties, the electric and magnetic form factors GEp and GMp of the proton have been obtained from elastic cross section data from many experiments. In the late 1990’s the new electron accelerator at Jefferson Lab (alias CEBAF) provided an alternate possibility to obtain GEp and GMp using polarized electrons and measuring the polarization of the recoiling proton. The very first of a series of experiments at JLab revealed that the GEp’s obtained by the two methods have a drastically different momentum transfer squared (Q2) behavior up to 8 GeV. After presentation of all data available today, I will discuss a few candidate possibilities to explain this difference in behavior of GEp results. I will also briefly discuss approved future experiments planned for the near future with the recently increased beam energies now available at JLab (12 GeV).