[Paper Review] A Collection of Polarized Parton Densities

Glenn A. Ladinsky|ArXiv.org|Jan 17, 1996

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper compiles and compares multiple parameterizations of polarized parton distribution functions (PDFs) using the CTEQ evolution package, enabling consistent evolution of various global fits. It presents a unified framework for spin-dependent PDFs, facilitating comparison and application in high-energy physics, particularly for HERA spin physics studies.

ABSTRACT

A significant number of parameterizations for the polarized parton densities have appeared in the literature. Using the CTEQ evolution package, these distributions have been evolved consistently preparatory to compilation into an integrated package in the spirit of PDFLIB by Plothow-Besch. Here, a comparison of a few of the more recent distributions are made. (Presented during the Workshop on the ``Prospects of Spin Physics at HERA'' held at DESY-Zeuthen, Germany, 28-31 August 1995.)

Motivation & Objective

• To compile and standardize multiple published parameterizations of polarized parton distribution functions (PDFs) for consistent use in phenomenological studies.
• To address the growing number of competing global fits for polarized PDFs by providing a unified, evolution-consistent framework.
• To support experimental and theoretical analysis in spin physics, particularly in the context of HERA's spin physics program.
• To enable direct comparison between recent polarized PDF fits through consistent evolution using the CTEQ package.
• To extend the PDFLIB-style framework to include polarized parton distributions, analogous to the global PDF library for unpolarized PDFs.

Proposed method

• Utilizes the CTEQ evolution package to evolve all selected polarized PDF parameterizations to a common factorization scale.
• Applies DGLAP evolution equations to ensure consistency across different global fits.
• Selects and includes multiple recent global fits of polarized quark and gluon distributions from global analyses.
• Employs standard phenomenological fitting procedures to ensure compatibility with experimental data from deep-inelastic scattering and other spin-dependent processes.
• Organizes the results into a structured, accessible format suitable for use in Monte Carlo simulations and phenomenological studies.
• Provides a reference framework for future updates and inclusion of new global fits as they emerge.

Experimental results

Research questions

• RQ1 How do different global fits of polarized parton distribution functions compare when consistently evolved using the same DGLAP framework?
• RQ2 What is the impact of varying input assumptions and experimental data sets on the resulting polarized PDF parameterizations?
• RQ3 Can a unified, evolution-consistent compilation of polarized PDFs improve the reliability and comparability of spin physics predictions?
• RQ4 How well do the current global fits describe the available spin-dependent deep-inlet scattering data at high momentum transfer?
• RQ5 What is the role of gluon polarization in the proton spin structure, and how do different fits vary in their predictions?

Key findings

• The paper successfully compiles a collection of polarized PDFs using consistent DGLAP evolution, enabling direct comparison between different global fits.
• Several recent polarized PDF parameterizations are shown to be consistent in their evolution behavior when processed through the CTEQ package.
• The study highlights differences in the gluon polarization distribution among various fits, particularly at low and high momentum fractions.
• The unified framework enables reliable predictions for spin asymmetries in deep-inelastic scattering and other high-energy processes.
• The compilation serves as a reference tool for future phenomenological studies and experimental analyses at HERA and beyond.
• The work paves the way for a standardized, community-adopted library of polarized PDFs, analogous to the existing PDFLIB for unpolarized PDFs.