Light-front transverse charge densities

TL;DR

This paper explores the interpretation of quark-distribution functions in the transverse plane, providing a model-independent way to visualize hadron structure and linking form factors to quark dynamics and orbital angular momentum.

Contribution

It introduces a model-independent approach to transverse charge densities, generalizes to particles with arbitrary spin, and presents Wigner distributions for unpolarized quarks in protons.

Findings

Transverse charge densities offer a semi-classical picture of quark dynamics.

Generalization to arbitrary spin reveals preferred electromagnetic coupling values.

Wigner distributions show orbital angular momentum effects in quark distributions.

Abstract

We discuss the recent interpretation of quark-distribution functions in the plane transverse to the light-cone direction. Such a mapping is model independent and allows one to build up multidimensional pictures of the hadron and to develop a semi-classical interpretation of the quark dynamics. We comment briefly the results obtained from the form factors of the nucleon. We show that a generalization to a target with arbitrary spin leads to a set of preferred values for the electromagnetic coupling characterizing structureless particles. Finally, we present the Wigner distribution for an unpolarized quark in an unpolarized proton and we propose an interpretation of the observed distortion as due to the orbital angular momentum of the quark.