Extraction of Spin-Dependent Parton Densities and Their Uncertainties

TL;DR

This paper presents a comprehensive global QCD analysis to extract spin-dependent parton distributions from polarized scattering data, employing advanced computational methods to improve accuracy and uncertainty estimation.

Contribution

It introduces efficient computational techniques for next-to-leading order analysis and compares methods for uncertainty estimation in spin-dependent parton densities.

Findings

Enhanced speed of calculations for global analysis

Quantitative constraints on quark, anti-quark, and gluon helicity distributions

Predictions for spin asymmetries in high-energy polarized collisions

Abstract

We discuss techniques and results for the extraction of the nucleon's spin-dependent parton distributions and their uncertainties from data for polarized deep-inelastic lepton-nucleon and proton-proton scattering by means of a global QCD analysis. Computational methods are described that significantly increase the speed of the required calculations to a level that allows to perform the full analysis consistently at next-to-leading order accuracy. We examine how the various data sets help to constrain different aspects of the quark, anti-quark, and gluon helicity distributions. Uncertainty estimates are performed using both the Lagrange multiplier and the Hessian approaches. We use the extracted parton distribution functions and their estimated uncertainties to predict spin asymmetries for high-transverse momentum pion and jet production in polarized proton-proton collisions at 500 GeV center-of-mass system energy at BNL-RHIC, as well as for W boson production.