Revisiting quark and gluon polarization in the proton at the EIC

TL;DR

This paper assesses how future EIC data could refine our understanding of quark and gluon spin contributions in the proton, highlighting the impact of assumptions and experimental limitations.

Contribution

It provides a comprehensive impact analysis of EIC measurements on proton spin structure, emphasizing the effects of extrapolation uncertainties and symmetry assumptions.

Findings

Different assumptions about asymmetry extrapolations significantly affect polarization estimates.

SU(3) symmetry constraints influence the extracted quark and gluon polarizations.

Luminosity limitations restrict the constraining power of parity-violating asymmetry measurements.

Abstract

We present a comprehensive impact study of future Electron-Ion Collider (EIC) data for parity-conserving and parity-violating polarization asymmetries on quark and gluon helicity distributions in the proton. The study, which is based on the JAM Monte Carlo global QCD analysis framework, explores the role of the extrapolation uncertainty and SU(3) flavor symmetry constraints in the simulated double-spin asymmetry, $A_{LL}$, at small parton momentum fractions $x$ and its effect on the extracted parton polarizations. We find that different assumptions about $A_{LL}$ extrapolations and SU(3) symmetry can have significant consequences for the integrated quark and gluon polarizations, for polarized proton, deuteron and $^3$He beams. For the parity-violating asymmetry, $A_{UL}$, we study the potential impact on the polarized strange quark distribution with different extrapolations of $A_{UL}$, finding the constraining power to be ultimately limited by the EIC machine luminosity.