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Spin-Orbit Correlations and Single-Spin Asymmetries

Matthias Burkardt

TL;DR

The paper tackles how spin-orbit correlations and orbital angular momentum (OAM) shape hadron structure by linking generalized parton distributions (GPDs), impact-parameter dependent PDFs (IPDs), and transverse-momentum dependent distributions (TMDs) within a light-cone framework. It shows that IPD distortions generated by transverse polarization relate to the GPD $E_q$ and the Pauli form factor $F_2$, giving a mechanism for the Sivers effect and predicting flavor-dependent signs $f_{1T}^{\perp u}<0$, $f_{1T}^{\perp d}>0$ with a testable SIDIS/DY sign change. The neutron's central charge density, inferred from the 2D Fourier transform of $F_1^q$, reveals negative central density tied to flavor OAM, supported by Ji relation analyses that yield $L_u \approx -L_d$. The tensor correlation $h_{1T}^{\perp}$ in TMDs provides a direct probe of quark OAM through $p$-wave components with $h_{1T}^{\perp}\sim (1-x)^5$, offering a coherent framework connecting spatial densities, spin-orbit dynamics, and spin asymmetries across SIDIS, Drell-Yan, and lattice studies.

Abstract

Several examples for the role of orbital angular momentum and spin-orbit correlations in hadron structure are discussed.

Spin-Orbit Correlations and Single-Spin Asymmetries

TL;DR

The paper tackles how spin-orbit correlations and orbital angular momentum (OAM) shape hadron structure by linking generalized parton distributions (GPDs), impact-parameter dependent PDFs (IPDs), and transverse-momentum dependent distributions (TMDs) within a light-cone framework. It shows that IPD distortions generated by transverse polarization relate to the GPD and the Pauli form factor , giving a mechanism for the Sivers effect and predicting flavor-dependent signs , with a testable SIDIS/DY sign change. The neutron's central charge density, inferred from the 2D Fourier transform of , reveals negative central density tied to flavor OAM, supported by Ji relation analyses that yield . The tensor correlation in TMDs provides a direct probe of quark OAM through -wave components with , offering a coherent framework connecting spatial densities, spin-orbit dynamics, and spin asymmetries across SIDIS, Drell-Yan, and lattice studies.

Abstract

Several examples for the role of orbital angular momentum and spin-orbit correlations in hadron structure are discussed.

Paper Structure

This paper contains 4 sections, 8 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Impact Parameter Dependent PDFs and the Sivers Effect
  3. Charge Density in the Center of the Neutron
  4. Tensor Correlations

Figures (2)

  • Figure 1: In SIDIS (a) the ejected (red) quark is attracted by the (anti-red) spectators. In contradistinction, in DY (b), before annihilating with the (red) active quark, the approaching (anti-red) antiquark is repelled by the (anti-red) spectators.
  • Figure 2: The transverse distortion of the parton cloud for a proton that is polarized into the plane, in combination with attractive FSI, gives rise to a Sivers effect for $u$ ($d$) quarks with a $\perp$ momentum that is on the average up (down).