A covariant model for the nucleon spin structure

TL;DR

This paper develops a covariant spectator quark model to describe the nucleon’s spin structure functions, fitting data for unpolarized and polarized scattering and predicting the less-measured g2 function for protons and neutrons.

Contribution

The paper introduces a covariant valence quark-diquark model with S, P, D components, fitted to data, and predicts the g2 structure function for nucleons.

Findings

Model accurately fits f(x) and g1(x) data

Predicts g2(x) functions for proton and neutron

Provides a covariant framework for nucleon spin structure

Abstract

We present the results of the covariant spectator quark model applied to the nucleon structure function $f(x)$ measured in unpolarized deep inelastic scattering, and the structure functions $g_1(x)$ and $g_2(x)$ measured in deep inelastic scattering using polarized beams and targets ($x$ is the Bjorken scaling variable). The nucleon is modeled by a valence quark-diquark structure with $S,P$ and $D$ components. The shape of the wave functions and the relative strength of each component are fixed by making fits to the deep inelastic scattering data for the structure functions $f(x)$ and $g_1(x)$. The model is then used to make predictions on the function $g_2(x)$ for the proton and neutron.