Physics of Gluon Helicity Contribution to Proton Spin

TL;DR

The totalgluon helicity in a polarized proton, measurable in high-energy scattering, is shown to be the large momentum limit of a gauge-invariant but nonlocal, frame-dependent gluon spin E × A⊥ in QCD, opening a door for a nonperturbative calculation of this quantity in lattice QCD.

Abstract

The total gluon helicity in a polarized proton, measurable in high-energy scattering, is shown to be the large momentum limit of a gauge-invariant but non-local, frame-dependent gluon spin $\vec{E}\times \vec{A}_\perp$ in QCD. This opens a door for a non-perturbative calculation of this quantity in lattice QCD, and also justifies using free-field expressions in the light-cone gauge as physical observables.

Figures (1)

• Figure 1: Matrix element of $\vec{E}\times\vec{A}_\perp$ in an asymptotic electron state.