Determining the helicity structure of the nucleon at the Electron Ion Collider in China

TL;DR

This paper explores how future data from the Electron-Ion Collider in China can improve understanding of quark polarization inside nucleons, using NLO QCD analysis and the Error PDF Updating Method.

Contribution

It demonstrates the potential of semi-inclusive and electron-$^3$He collision data to better constrain flavor-separated helicity distributions at EicC.

Findings

Semi-inclusive data effectively separate flavor distributions.

Electron-$^3$He collisions improve constraints on neutron-like data.

Uncertainty reduction in helicity PDFs for x > 0.005.

Abstract

Understanding how sea quarks behave inside a nucleon is one of the most important physics goals of the proposed Electron-Ion Collider in China (EicC), which is designed to have 3.5 GeV polarized electron beam (80% polarization) colliding with 20 GeV polarized proton beam (70% polarization) at instantaneous luminosity of $2 \times 10^{33} {\rm cm}^{-2} {\rm s}^{-1}$. A specific topic at EicC is to understand the polarization of individual quarks inside a longitudinally polarized nucleon. The potential of various future EicC data, including the inclusive and semi-inclusive deep inelastic scattering data from both doubly polarized electron-proton and electron-$^3{\rm He}$ collisions, to reduce the uncertainties of parton helicity distributions is explored at the next-to-leading order in QCD, using the Error PDF Updating Method Package ({\sc ePump}) which is based on the Hessian profiling method. We show that the semi-inclusive data are well able to provide good separation between flavour distributions, and to constrain their uncertainties in the $x>0.005$ region, especially when electron-$^3{\rm He}$ collisions, acting as effective electron-neutron collisions, are taken into account. To enable this study, we have generated a Hessian representation of the DSSV14 set of PDF replicas, named DSSV14H PDFs.