Unveiling the Proton Spin Decomposition at a Future Electron-Ion Collider

TL;DR

This paper assesses how a future Electron-Ion Collider could improve understanding of the proton's spin structure by constraining helicity parton distributions, using global QCD analyses and projections based on pseudo-data and recent experiments.

Contribution

It provides a detailed evaluation of the potential of a future Electron-Ion Collider to refine the decomposition of proton spin, especially the gluon contribution, through advanced analysis techniques.

Findings

Projected constraints on gluon helicity distribution

Evidence for significant gluon polarization from current data

Potential for improved spin decomposition at future collider

Abstract

We present a detailed assessment of how well a future Electron-Ion Collider could constrain helicity parton distributions in the nucleon and, therefore, unveil the role of the intrinsic spin of quarks and gluons in the proton's spin budget. Any remaining deficit in this decomposition will provide the best indirect constraint on the contribution due to the total orbital angular momenta of quarks and gluons. Specifically, all our studies are performed in the context of global QCD analyses based on realistic pseudo-data and in the light of the most recent data obtained from polarized proton-proton collisions at BNL-RHIC that have provided evidence for a significant gluon polarization in the accessible, albeit limited range of momentum fractions. We also present projections on what can be achieved on the gluon's helicity distribution by the end of BNL-RHIC operations. All estimates of current and projected uncertainties are performed with the robust Lagrange multiplier technique.