Valence Quark Polarization In the Nucleon And the Deuteron Data

TL;DR

This paper uses the valon model to analyze the nucleon and deuteron spin structure, finding that valence quarks carry about 40% of the spin, with gluons and orbital angular momentum accounting for the rest, and suggesting a smaller value for a_8 than previously thought.

Contribution

It introduces a valon model-based analysis of nucleon spin, challenging the full SU(3) symmetry assumption and aligning with recent experimental data.

Findings

Valence quarks carry about 40% of nucleon spin.

Sea quark contribution is negligible and consistent with zero.

Proposed smaller a_8 value than hyperon decay inference.

Abstract

Within the framework of the so-called "valon" model, we argue that a substantial part of the nucleon spin, about 40%, is carried by the polarized valence quarks. The remaining is the result of cancellations between gluon polarization and the orbital angular momentum, where the gluon polarization is the dominant one. It is shown that the sea quark contribution to the spin of any hadron is simply marginal and consistent with zero. Our findings point to a substantially smaller value for a_8 thaninferred from hyperon- $\beta$ decay, suggesting that fullSU(3) symmetric assumption needs to be reconsidered. New and emerging experimental data tend to support this finding. Finally, we show that within the model described here the experimental data on the polarized structure functions $g_{1}^{p,n,d}$ are reproduced.