Exploring the proton spin structure

TL;DR

This paper reviews the current understanding and recent progress in unraveling the complex spin structure of the proton within quantum field theory, highlighting measurable decompositions and future research directions.

Contribution

It provides a comprehensive summary of the state-of-the-art in proton spin decomposition methods and discusses recent theoretical and experimental advancements.

Findings

Recent developments in measurable proton spin decompositions

Challenges in extending non-relativistic concepts to quantum field theory

Future prospects for understanding proton spin structure

Abstract

Understanding the spin structure of the proton is one of the main challenges in hadronic physics. While the concepts of spin and orbital angular momentum are pretty clear in the context of non-relativistic quantum mechanics, the generalization of these concepts to quantum field theory encounters serious difficulties. It is however possible to define meaningful decompositions of the proton spin that are (in principle) measurable. We propose a summary of the present situation including recent developments and prospects of future developments.