Effect of Orbital Angular Momentum on Valence-Quark Helicity Distributions

Understand

We study the quark helicity distributions at large x in perturbative QCD, taking into account contributions from the valence Fock states of the nucleon which have nonzero orbital angular momentum.

• These states are necessary to have a nonzero anomalous magnetic moment.
• We find that the quark orbital angular momentum contributes a large logarithm to the negative helicity quark distributions in addition to its power behavior, scaling as (1-x)^5\log^2(1-x) in the limit of x\to 1.
• Our analysis shows that the ratio of the polarized over unpolarized down quark distributions, \Delta d/d, will still approach 1 in this limit.