Spin and Orbital Angular Momentum Distribution Functions of the Nucleon

TL;DR

This paper predicts the distribution of spin and orbital angular momentum within the nucleon using the chiral quark soliton model, highlighting a small quark spin fraction and a large orbital contribution.

Contribution

It provides a theoretical prediction of nucleon spin and orbital angular momentum distributions within an effective quark model, emphasizing the significant orbital angular momentum component.

Findings

Quark spin fraction is approximately 0.35.

Orbital angular momentum accounts for about 65% of the nucleon spin.

Large orbital angular momentum influences the scale dependence of nucleon spin content.

Abstract

A theoretical prediction is given for the spin and orbital angular momentum distribution functions of the nucleon within the framework of an effective quark model of QCD, i.e. the chiral quark soliton model. An outstanding feature of the model is that it predicts fairly small quark spin fraction of the nucleon $\Delta \Sigma \simeq 0.35$, which in turn dictates that the remaining 65% of the nucleon spin is carried by the orbital angular momentum of quarks and antiquarks at the model energy scale of $Q^2 \simeq 0.3 {GeV}^2$. This large orbital angular momentum necessarily affects the scenario of scale dependence of the nucleon spin contents in a drastic way.