Nucleon Spin Content from Elastic Form Factor Data

Abstract

I use the formalism of skewed parton distributions (SPD) to describe elastic form factors of the nucleon. The results are consistent with approximate dipole behavior of $G_{Mp}(Q^2)$ and recent JLab data for the ratio of the proton form factors $G_{Ep}/G_{Mp}$ at $Q^2\leq 3.5$ GeV$^2$. Using the Angular Momentum Sum Rule, I obtain a numerical estimate for the valence quark contributions to the nucleon spin at the level of 50%, with their orbital angular momentum {\it included}. When combined with polarized DIS measurements, this result indicated that the orbital angular momentum of quarks contributes about 25% to the nucleon spin.