Next-to-Leading Order Radiative Parton Model Analysis of Polarized Deep Inelastic Scattering

TL;DR

The paper addresses how to extract spin-dependent parton distributions from polarized deep inelastic scattering using a consistent next-to-leading order QCD framework within the radiative parton model. It derives analytic Mellin-space solutions for the NLO evolution of polarized densities in the $\overline{MS}$ scheme and performs quantitative fits to $A_1^N(x,Q^2)$ data, yielding two plausible polarized PDFs under standard and valence SU(3) symmetry scenarios. The results show perturbative stability between LO and NLO and reveal a non-negligible $Q^2$-dependence of spin observables, with a sizable total gluon helicity $\Delta g$ around 1.7 at higher $Q^2$ and a Bjorken sum rule-consistent description of $\Gamma_1^{p,n}$. These findings improve interpretation of current polarized DIS data and inform expectations for future measurements, including at HERA, by providing robust NLO spin-dependent parton distributions and associated uncertainties. A Fortran package implementing the fitted densities is available for practical phenomenology.

Abstract

A next-to-leading order QCD analysis of spin asymmetries and structure functions in polarized deep inelastic lepton nucleon scattering is presented within the framework of the radiative parton model. A consistent NLO formulation of the $Q^2$-evolution of polarized parton distributions yields two sets of plausible NLO spin dependent parton distributions in the conventional $\overline{\rm{MS}}$ factorization scheme. They respect the fundamental positivity constraints down to the low resolution scale $Q^2=μ^2_{NLO}=0.34\,{\rm{GeV}}^2$. The $Q^2$-dependence of the spin asymmetries $A_1^{p,n,d}(x,Q^2)$ is similar to the leading-order (LO) one in the range $1\le Q^2\le 20\,{\rm{GeV}}^2$ and is shown to be non-negligible for $x$-values relevant for the analysis of the present data and possibly forthcoming data at HERA.