An analysis of polarized parton distribution functions with nonlinear QCD evolution equations

TL;DR

This paper derives polarized parton distribution functions using a QCD analysis with nonlinear evolution equations, emphasizing the role of gluons in proton spin and achieving good agreement with experimental data.

Contribution

It introduces a simple four-parameter model for polarized PDFs based on nonlinear QCD evolution with parton recombination, highlighting the importance of gluons in proton spin.

Findings

Polarized gluon distribution is positive and significant.

The model reproduces experimental spin-dependent structure functions.

Smaller uncertainties in sea quark and gluon distributions due to fewer parameters.

Abstract

We present the polarized parton distribution functions from a QCD analysis of the worldwide polarized deep inelastic scattering data, based on the dynamical parton distribution model. All the sea quarks and gluons are dynamically generated from QCD radiations, with the nonperturbative input contains only the polarized valence quark distributions. This approach leads to a simple parametrization, which has only four free parameters. In the analysis, we apply the DGLAP equations with parton-parton recombination corrections. The parameterized nonperturbative input at an extremely low $Q_0^2$ reproduces well the spin-dependent structure functions measured at high $Q^{2}$. Comparisons with experimental observations and some other polarized parton distribution functions are also shown. Our results are in good agreement with the experimental data and consistent with some other parameterized models. Furthermore, our analysis gives the positive polarized gluon distribution and it suggests that the gluon distribution plays an important role to the proton spin content. The polarized antiquark distributions are non-zero at high $Q^2$ but quite small compared to polarized valence quark distribution, based on this dynamical parton model analysis. This analysis shows smaller statistical uncertainties for the polarized sea quark and gluon distributions, thanks to the fewer free parameters used for the parametrization of the initial polarized PDFs.