Polarized Structure of Nucleon in the Valon Representation

TL;DR

This paper uses the valon model to calculate the spin structure functions of nucleons, showing good agreement with experimental data and revealing the significant role of gluons and orbital angular momentum in nucleon spin.

Contribution

It introduces a valon-based approach to compute nucleon spin structure functions, incorporating perturbative QCD effects and analyzing gluon and orbital contributions.

Findings

Sea quark contribution to proton spin is negligible.

Gluon contribution increases with Q^2, reaching about 60%.

Orbital angular momentum component is sizable and sensitive to initial scale.

Abstract

We have utilized the concept of valon model to calculate the spin structure functions of proton, neutron and deuteron. The valon structure itself is universal and arises from the perturbative dressing of the valence quark in QCD. Our results agree rather well with all the relevant experimental data on $g_{1}^{p, n, d}$ and $g_{A}/g_{v}$, and suggests that the sea quark contribution to the spin of proton is consistent with zero. It also reveals that while the total quark contribution to the spin of valon is almost constant at $Q^{2}>=1$ the gluon contribution grows with the increase of $Q^2$ and hence requiring a sizable negative orbital angular momentum component $L_z$. This component along with the singlet and non-singlet parts are calculated in the Next-to-Leading order in QCD. We speculate that gluon contribution to the spin content of the proton is about 60% for all $Q^2$ values. Finally, we show that the size of gluon polarization and hence, $L_{z}$, is sensitive to the initial scale$Q_{0}^{2}$.