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

Assuming the angular momentum of a polarized proton JZ=1/2 to be the resultant of the total spin SZ and total orbital momentum LZ of its parton constituents (quarks and antiquarks), we find SZ=1/2(3F-D), LZ=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 LZ, interpreted geometrically, implies that a polarized proton possesses a significant amount of rotation. On the assumption that SZ and LZ are dominated by P and N quarks, an estimate is made of the separate contribution of these constituents.