Polarized Antimatter in the Proton from Global QCD Analysis

TL;DR

This paper conducts a comprehensive global QCD analysis to determine the polarized parton distribution functions and fragmentation functions, providing new insights into the proton's spin structure and antiquark polarization ratios.

Contribution

It presents the first simultaneous global analysis of spin-dependent and spin-averaged PDFs with fragmentation functions, incorporating recent experimental data for improved accuracy.

Findings

Robust extraction of polarized light quark sea asymmetry $oldsymbol{ riangle ar{u} - riangle ar{d}}$

Determination of antiquark polarization ratios $oldsymbol{ riangle ar{u}/ar{u}}$ and $oldsymbol{ riangle ar{d}/ar{d}}$

Insights into the signs of truncated contributions to proton spin from light antiquarks

Abstract

We present the first simultaneous global QCD analysis of spin-dependent parton distribution functions alongside their spin-averaged counterparts and pion, kaon, and unidentified hadron fragmentation functions. This analysis includes all data relevant for constraining the polarized light quark sea asymmetry $\Delta \bar{u} - \Delta \bar{d}$, in particular the latest polarized $W$-lepton production data from the STAR collaboration at RHIC and semi-inclusive deep inelastic scattering data from COMPASS, allowing the most robust extraction available with minimal theoretical assumptions. We also extract a self-consistent set of antiquark polarization ratios $\Delta \bar{u}/\bar{u}$ and $\Delta \bar{d}/\bar{d}$ and determine the signs of the truncated contributions to the proton spin from the light antiquarks.