Study of the proton structure by measurements of polarization transfers in Real Compton scattering at the Th. Jeerson Natl. Lab

rst direct evidence that the proton has an internal structure came from a measurement of its magnetic moment in 1933 by O. Stern. In the 1950s, a series of experiments led by R. Hofstadter at SLAC (Stanford) using elastic electron scattering to explore nuclear structure, measured for the rst time the electric and magnetic form factors of the proton, rmly establishing that the proton has an extended charge and magnetic distributions. In the late 1960s the rst inclusive Deep Inelastic Scattering (DIS) experiments were performed at SLAC with an electron beam. They showed the scaling behavior of the structure functions for high momentum transfer Q 2 , interpreted by Bjorken and Feynman as evidence of charged constituents inside the proton. The DIS experiments allowed also the extraction of the unpolarized parton distribution functions (PDF) 1 . Existence of the gluon (the gauge bosons in Quantum Chromodynamics) in the nucleon has been observed at DESY (Hamburg). Another remarkable discovery made at CERN by the EMC Collaboration [1] showed that the total spin of the quarks contributes at most by 25% to the spin of the nucleon (\spin crisis"); the nucleon spin SN can be decomposed into three dierent components: SN = 1