Nucleon Spin Structure And Quark Helicity Decomposition

Using the results for the first moments of the proton and deuteron spin structure functions g(1)(p,d) measured at the SLAC experiment E143, we compare the conventional method of obtaining from those moments the quark helicity contributions to the proton spin assumming SU(3)(flavor) symmetry (which implies a strange quark sea helicity Delta s not equal 0) to the results obtained assuming Delta s=0. We conclude that current experimental uncertainties cannot rule out the latter. Using Delta s=0 we extract the SU(3)(flavor) F and D terms directly from the first moments, which give an estimate of possible symmetry breaking.