Towards the determination of the gluon helicity distribution in the nucleon from lattice quantum chromodynamics

TL;DR

This paper presents the first lattice QCD calculation of the gluon helicity distribution in the nucleon using the Ioffe-time pseudo-distribution approach, providing insights into the proton spin structure from first principles.

Contribution

It introduces a novel lattice QCD method to determine the gluon helicity distribution via the Ioffe-time pseudo-distribution, demonstrating feasibility and initial results.

Findings

Good agreement with global analyses.

Evidence of nonzero gluon spin contribution.

Pseudo-distribution approach is viable for proton spin studies.

Abstract

We present the first exploratory lattice quantum chromodynamics (QCD) calculation of the polarized gluon Ioffe-time pseudo-distribution in the nucleon. The Ioffe-time pseudo-distribution provides a frame-independent and gauge-invariant framework to determine the gluon helicity in the nucleon from first principles. We employ a high-statistics computation using a $32^3\times 64$ lattice ensemble characterized by a $358$ MeV pion mass and a $0.094$ fm lattice spacing. We establish the pseudo-distribution approach as a feasible method to address the proton spin puzzle with successive improvements in statistical and systematic uncertainties anticipated in the future. Within the statistical precision of our data, we find a good comparison between the lattice determined polarized gluon Ioffe-time distribution and the corresponding expectations from the state-of-the-art global analyses. We find a hint for a nonzero gluon spin contribution to the proton spin from the model-independent extraction of the gluon helicity pseudo-distribution over a range of Ioffe-time, $\nu\lesssim 9$.