The Spin Dependent Parton Distribution Functions and their Moments

In the quark parton model (QPM), polarized structure function g1 is directly related to contributions of the individual quark flavors to the overall spin of the nucleon. Sum rules based on this simple model have provided fertile ground for understanding the origin of the nucleon spin in terms of quark degrees of freedom. Our next-to-leading-order (NLO) analyses of the world g1 data based on the Jacobi polynomial expansion method have provided indirect information about the components of the nucleon's spin. Moreover, we study the dependence of our results to the number of Jacobi polynomial expansion terms in this paper. (authors)