The Sivers parton distribution function has been predicted to obey a particular "universality relation", namely to have opposite sign in semi-inclusive deeply inelastic scattering (SIDIS) and the Drell-Yan process. We discuss how, on the basis of present HERMES data, this remarkable prediction of the QCD factorization approach to the description of single spin asymmetries related to the Sivers effect could be checked experimentally in future experiments at PAX and COMPASS.

The Sivers function is extracted from HERMES data on single spin asymmetries in semi-inclusive deeply inelastic scattering. Our analysis use a simple Gaussian model for the distribution of transverse parton momenta, together with the flavor dependence given by the leading 1/Nc approximation and a neglect of the Sivers antiquark distribution. We find that within the errors of the data these approximations are sufficient.

On the basis of a fit to the Sivers effect in deep-inelastic scattering, we make predictions for singlespin asymmetries in the Drell-Yan process at BNL RHIC.

A comparison is given of the various recently published extractions of the Sivers functions from the HERMES and COMPASS data on single-transverse spin asymmetries in semi-inclusive deeply inelastic scattering.

The Sivers function is extracted from HERMES data on single spin asymmetries in semi-inclusive deeply inelastic scattering. Our analysis use a simple Gaussian model for the distribution of transverse parton momenta, together with the flavor dependence given by the leading 1/Nc approximation and a neglect of the Sivers antiquark distribution. We find that within the errors of the data these approximations are sufficient.