RESULTS AND INTERPRETATIONS OF THE SPIN STRUCTURE EXPERIMENTS AT SLAC

In the recent experiments E154 and E155 at SLAC the spin-dependent structure functions g{sub 1}{sup n}, g{sub 1}{sup p}, and g{sub 1}{sup d} of the neutron, proton, and deuteron were measured by scattering longitudinally polarized 48:3 GeV electrons off longitudinally polarized targets. We report on the measurement of g{sub 1}{sup n} by E154, and on the preliminary results on g{sub 1}{sup 0} from E155. The SLAC results provide the most precise determination to date of the polarized structure functions. We observe relatively large values of g{sub 1}{sup n} at low x that call into question the reliability of data extrapolation to x -> 0. Such divergent behavior disagrees with predictions of the conventional Regge theory, but is qualitatively explained by perturbative QCD. We perform a Next-to-Leading Order perturbative QCD analysis of the world data on the nucleon spin-dependent structure functions. Using the parameterizations of the helicity-dependent parton distributions obtained in the analysis, we evolve the data to Q{sup 2} = 5 GeV{sup 2}, determine the first moments of the polarized structure functions of the proton and neutron, and find agreement with the Bjorken sum rule.