Overview of nucleon form factor experiments with 12 GeV at Jefferson Lab

摘要

Since the R. Hofstadter pioneering experiments in the '50s, the measurements of the electromagnetic space-like nucleon form factors (FF's) have been a precious source of information for the understanding of the internal structure of the nucleons. In the last 15 years, the polarization transfer experiments at the Thomas Jefferson National Accelerator Facility (JLab) have undermined our view of the mechanism of the electron scattering and renewed critical interest in the FF measurements. In the coming years, JLab, with its upgraded 12 GeV polarized, high intensity, electron beam combined to new targets and readout equipments, will offer unprecedented opportunities to extend the current proton and neutron FF's measurements to higher momentum transfer Q~2 and to improve statistical and uncertainties at lower Q~2, where the nucleon size can be accurately investigated. The measurements at high Q~2 will provide also new insights on the elusive quark orbital angular momenta, will contribute to constraint two of the nucleon Generalized Parton Distributions that are expected to describe more consistently the nucleon structure, and in general will test the validity of quite a few fundamental nucleon models in a region of transition between perturbative and non perturbative regimes. A selection of the relevant properties of the FF's, and the main results of JLab are shortly reviewed; the new proposed and approved experiments on FF's at JLab are presented addressing some key details, the expected experimental achievements and the new equipment designed for them.