Nucleon form factors, generalized parton distributions and quark angular momentum
We extract the individual contributions from u and d quarks to the Dirac and Pauli form factors of the proton, after a critical examination of the available measurements of electromagnetic nucleon form factors. From this data we determine generalized parton distributions for valence quarks, assuming a particular form for their functional dependence. The result allows us to study various aspects of nucleon structure in the valence region. In particular, we evaluate Ji's sum rule and estimate the total angular momentum carried by valence quarks at the scale mu = 2 GeV to be J_v^u = 0.230 +0.009 -0.024 and J_v^d = -0.004 +0.010 -0.016.