SPIN-DEPENDENT PARTON DISTRIBUTIONS FROM POLARIZED STRUCTURE-FUNCTIONDATA

In the past year, polarized deep inelastic scattering experiments at C ERN and SLAC have obtained structure function measurements off proton, neutron and deuteron targets at a level of precision never before ach ieved. The measurements can be used to test the Bjorken and Ellis-Jaff e sum rules, and also to obtain information on the parton distribution s in polarized nucleons. We perform a global leading-order QCD fit to the proton deep inelastic data in order to extract the spin-dependent parton distributions. By using parametric forms which are consistent w ith theoretical expectations at large and small x, we find that the qu ark distributions are now rather well constrained. We assume that ther e is no significant intrinsic polarization of the strange quark sea. T he data are then consistent with a modest amount of the proton's spin carried by the gluon, although the shape of the gluon distribution is not well constrained, and several qualitatively different shapes are s uggested. The spin-dependent distributions we obtain can be used as in put to phenomenological studies for future polarized hadron-hadron and lepton-hadron colliders.