QCD analysis of polarized parton densities

Abstract
We present the results of QCD fits to global data on deep-inelastic polarized lepton-hadron scattering. We find that it is possible to fit the data with strongly broken SU(2) flavor for the polarized sea densities. This can be tested in W production at the polarized BNL RHIC. The data fail to pin down polarized singlet sea quark and gluon densities. We explore the uncertainties in detail and show that improvement in statistics, achievable at the polarized DESY HERA for measurement of A1 at moderately low values of x, have large payoffs in terms of the improvement in measurement of gluon densities.