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

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 $Q^2=\mu^2_{NLO}=0.34\,{\rm{GeV}}^2$. 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.