Sivers effect in semi-inclusive DIS and in the Drell-Yan process

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.