QCD Anomaly and Spin Density of Quark and Gluon in Proton

From the Altarelli-Parisi equation for the helicity difference distributions of quarks and gluon in a polarized proton, we have known that the first moment of gluon distributions is proportional to In(Q~2/A~2) at the leading approximation and the polarized structure function of proton can be written as