Polarised parton densities from the fits to the deep inelastic spin asymmetries on nucleons

Abstract

We have made next to leading order QCD fit to the deep inelastic spin asymmetries on nucleons and we have determined polarised quark and gluon densities. The functional form for such distributions was inspired by the unpolarised ones given by MRST (Martin, Roberts, Stirling and Thorne) fit. In addition to usually used data points (averaged over $Q^2$) we have also considered the sample containing points with the same $x$ and different $Q^2$. Our fits to both groups of data give very similar results. For the integrated quantities we get rather small gluon polarisation. For the non averaged data the best fit is obtained with vanishing gluon contribution at $Q^2=1\mathrm{Ge}{\mathrm{V}}^2$. For comparison models with alternative assumptions about quark sea and in particular strange sea behaviour are discussed.

Comments: 20 pages, latex, 7 eps-figures, due to an error in one of input parameters small changes in numerical results, main conclusions unchanged