Tensor-polarized parton distribution functions for spin-1 hadrons

TL;DR

This paper reviews tensor-polarized parton distribution functions in spin-1 hadrons, highlighting their unique structure functions, recent theoretical developments, and experimental prospects at Jefferson Lab, advancing understanding of spin physics beyond spin-1/2 nucleons.

Contribution

It provides a comprehensive overview of tensor-polarized parton distributions, including transverse-momentum-dependent functions and higher-twist effects, with emphasis on recent theoretical and experimental developments.

Findings

Tensor-polarized structure functions $b_1$ and $b_2$ offer new insights into spin-1 hadron structure.

Gluon transversity in spin-1 hadrons is a novel aspect not present in spin-1/2 nucleons.

Upcoming experiments at Jefferson Lab aim to measure tensor-polarized distributions.

Abstract

Spin-1 hadrons contain different aspects of spin physics from the ones of the spin-1/2 nucleon because of the existence of tensor-polarized structure functions. In the charged-lepton deep inelastic scattering from a spin-1 hadron or nucleus, such as the deuteron, there are leading-twist structure functions $b_1$ and $b_2$. In addition, there exists a gluon transversity which does not exist in the spin-1/2 nucleon. In the deuteron, these observables could probe interesting dynamical aspects beyond a simple bound system of a proton and a neutron. In addition, there are recent theoretical studies on higher-twist distributions. Tensor-polarized deuteron experiments are now under preparation at the Thomas Jefferson National Accelerator Facility, so that the topic of polarized deuteron is expected to become one of exciting fields in hadron physics. This paper is a brief overview on the tensor-polarized parton distribution functions, including transverse-momentum-dependent parton distributions and fragmentation functions up to twist 4.