Angular momentum composition of the proton in the quark-parton model

Assuming the angular momentum of a polarized proton $J_Z=\frac{1}{2}$ to be the resultant of the total spin $S_Z$ and total orbital momentum $L_Z$ of its parton constituents (quarks and antiquarks), we find $S_Z=\frac{1}{2}(3F-D)$, $L_Z=\frac{1}{2}(1-3F+D)$. The approzimation employed is the same as that leading to the Ellis-Jaffe sum rules for polarized electron-nucleon scattering. The result for $L_Z$, interpreted geometrically, implies that a polarized proton possesses a significant amount of rotation. On the assumption that $S_Z$ and $L_Z$ are dominated by P and N quarks, an estimate is made of the separate contribution of these constituents.