Transverse (Spin) Structure of Hadrons

TL;DR

This paper explores how the transverse polarization of hadrons affects their internal parton distributions, revealing deformations linked to spin asymmetries and magnetic moments, and connecting these to observable phenomena like the Sivers function.

Contribution

It establishes a relationship between transverse deformation of parton distributions and the signs of the Sivers function and quark-gluon correlations based on magnetic moments.

Findings

Transverse polarization causes measurable deformation in parton distributions.

The sign of deformation correlates with the nucleon’s anomalous magnetic moments.

This connection explains the signs of the Sivers function for u and d quarks.

Abstract

Parton distributions in impact parameter space, which are obtained by Fourier transforming GPDs, exhibit a significant deviation from axial symmetry when the target and/or quark are transversely polarized. Connections between this deformation and transverse single-spin asymmetries as well as with quark-gluon correlations are discussed. The sign of transverse deformation of impact parameter dependent parton distributions in a transversely polarized target can be related to the sign of the contribution from that quark flavor to the nucleon anomalous magnetic moment. Therefore, the signs of the Sivers function for $u$ and $d$ quarks, as well as the signs of quark-gluon correlations embodied in the polarized structure function $g_2$ can be understood in terms of the proton and neutron anomalous magnetic moments.