Distribution Functions of the Nucleon and Pion in the Valence Region

TL;DR

This paper reviews experimental and theoretical insights into the valence-quark distribution functions of nucleons and pions, emphasizing the importance of upcoming experiments and the need for theoretical advancements to deepen our understanding of hadron structure.

Contribution

It provides a comprehensive overview of current experimental data and theoretical approaches to valence-quark distributions, highlighting future experimental prospects and the necessity for theoretical adaptation.

Findings

Valence-quark distributions are crucial for understanding hadron structure.

Upcoming experiments at Jefferson Lab and electron-ion colliders will provide new data.

Theoretical explanations require embracing nonperturbative quantum field theory methods.

Abstract

We provide an experimental and theoretical perspective on the behavior of unpolarized distribution functions for the nucleon and pion on the valence-quark domain; namely, Bjorken-x \gtrsim 0.4. This domain is key to much of hadron physics; e.g., a hadron is defined by its flavor content and that is a valence-quark property. Furthermore, its accurate parametrization is crucial to the provision of reliable input for large collider experiments. We focus on experimental extractions of distribution functions via electron and muon inelastic scattering, and from Drell-Yan interactions; and on theoretical treatments that emphasize an explanation of the distribution functions, providing an overview of major contemporary approaches and issues. Valence-quark physics is a compelling subject, which probes at the heart of our understanding of the Standard Model. There are numerous outstanding and unresolved challenges, which experiment and theory must confront. In connection with experiment, we explain that an upgraded Jefferson Lab facility is well-suited to provide new data on the nucleon, while a future electron ion collider could provide essential new data for the mesons. There is also great potential in using Drell-Yan interactions, at FNAL, J-PARC and GSI, to push into the large-x domain for both mesons and nucleons. We argue furthermore that explanation, in contrast to modeling and parametrization, requires a widespread acceptance of the need to adapt theory: to the lessons learnt already from the methods of nonperturbative quantum field theory; and a fuller exploitation of those methods.