Revisiting Helicity Parton Distributions at a Future Electron-Ion Collider

TL;DR

This study evaluates how future Electron-Ion Collider data will significantly improve the understanding of helicity parton distributions, especially at low x, and enable flavor separation of sea quarks, surpassing current limitations.

Contribution

It demonstrates the potential of future EIC inclusive and semi-inclusive data to greatly enhance helicity distribution determinations and flavor separation capabilities.

Findings

Significant improvement in helicity distributions at low x.

Enhanced gluon polarization constraints at higher energies.

First-time flavor separation of sea quarks from semi-inclusive data.

Abstract

We studied the impact of future Electron Ion Collider inclusive and semi-inclusive polarized deep inelastic scattering data will have on the determination of the helicity parton distributions. Supplementing the Monte Carlo sampling variant of the DSSV14 analysis with pseudo-data on polarized inclusive and semi-inclusive electron-proton deep inelastic scattering with updated uncertainty estimates and for two different center-of-mass-system energies, $\sqrt{s}=44.7$ GeV and $\sqrt{s}=141.4$ GeV respectively, and on inclusive electron-helium collisions at $\sqrt{s}=115.2$ GeV, we find a remarkable improvement in the determination of the helicity distributions, specially at low parton momentum fraction $x$. While inclusive electron-proton data at the lowest energy configuration constrain significantly the gluon polarization down to $x \sim 10^{-4}$, the higher energy configuration strengthens the constraint and extends it one decade further. On the other hand, semi-inclusive data achieves the hitherto elusive flavor separation for sea quarks that can not be obtained from any other inclusive electromagnetic measurement. Collisions with helium complement inclusive proton measurements, pushing the constraints on the combined quark plus anti-quark $u, d$ and $s$ polarizations to an unprecedented level.