Spin and angular momentum in the nucleon

TL;DR

This paper employs covariant spectator theory to model nucleon structure functions, fitting experimental data and revealing a significant D-wave component in the nucleon wave function.

Contribution

It introduces a valence quark-diquark model within CST that accurately fits unpolarized and polarized DIS data, highlighting the importance of D-wave components.

Findings

A large D-wave component (~35%) in the nucleon wave function.

Successful fit to f(x) and g1(x) data.

One solution also fits g2(x) well.

Abstract

Using the covariant spectator theory (CST), we present the results of a valence quark-diquark model calculation of the nucleon structure function f(x) measured in unpolarized deep inelastic scattering (DIS), and the structure functions g1(x) and g2(x) measured in DIS using polarized beams and targets. Parameters of the wave functions are adjusted to fit all the data. The fit fixes both the shape of the wave functions and the relative strength of each component. Two solutions are found that fit f(x) and g1(x), but only one of these gives a good description of g2(x). This fit requires the nucleon CST wave functions contain a large D-wave component (about 35%) and a small P-wave component (about 0.6%). The significance of these results is discussed.