Experimental evidence for simple relations between unpolarized and polarized parton distributions.

The Pauli exclusion principle is advocated for constructing the proton and neutron deep inelastic structure functions in terms of Fermi-Dirac distributions that we parametrize with very few parameters. It allows a fair description of the recent NMC data on F p 2 (x, Q ) and F n 2 (x, Q ) at Q = 4GeV , as well as the CCFR neutrino data at Q = 3 and 5GeV . We also make some reasonable and simple assumptions to relate unpolarized and polarized quark parton distributions and we obtain, with no additional free parameters, the spin dependent structure functions xg 1(x, Q ) and xg 1 (x, Q ). Using the correct Q evolution, we have checked that they are in excellent agreement with the very recent SMC proton data at Q = 10GeV 2 and the SLAC neutron data at Q = 2GeV . Number of figures : 6 May 1994 CPT-94/P.3032 anonymous ftp or gopher: cpt.univ-mrs.fr Many years ago Feynman and Field made the conjecture that the quark sea in the proton may not be flavor symmetric, more precisely d̄ > ū, as a consequence of Pauli principle which favors dd̄ pairs with respect to uū pairs because of the presence of two valence u quarks and only one valence d quark in the proton. This idea was confirmed by the results of the NMC experiment on the measurement of proton and neutron unpolarized structure functions, F2(x). It yields a fair evidence for a defect in the Gottfried sum rule and one finds