Phenomenological approach to unpolarized and polarized parton distributions and experimental tests

We recall our recent description of quark parton densities of the proton at Q2=4GeV2 in terms of Fermi-Dirac distributions parametrized with very few free parameters. We have also proposed some simple assumptions to relate unpolarized and polarized quark parton densities which lead to a fair description of the spin-dependent structure functions xgp1(x,Q2) and xgn1(x,Q2) at low Q2. We will show the predictions we obtain after a straightforward DGLAP Q2 evolution and comparison in a much broader x and Q2 range, with several recent and accurate deep-inelastic scattering data. In particular, we will see that we get an excellent agreement with the sharp rise of Fep2(x,Q2) for small x, recently observed at HERA. Finally, we give several predictions for lepton pair and gauge boson production in pp and pn collisions at high energies which will be tested in the future at RHIC. (orig.)