Determination of polarised parton distributions in the nucleon - next to leading order QCD analysis

Abstract

We have made next to leading order QCD fit to the deep inelastic spin asymmetries on nucleons and we determined polarised quark and gluon densities. The functional form for such distributions was inspired by the Martin, Roberts and Stirling fit for unpolarised case. In addition to usually used data points (averaged over $x$ and $Q^2$) we have also considered the sample containing points with similar $x$ and different $Q^2$. It seems that splitting of quark densities into valence and sea contribution is strongly model dependent and only their sum (i.e., $Δu$ and $Δd$) can be precisely determined from the data. Integrated polarised gluon contribution, contrary to some expectations, is relatively small and the sign of it depends on the fact which sample of data points is used.