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Using QCD motivated and phenomenological considerations, we construct x dependent polarized parton distributions, which evolve under GLAP evolution, satisfy DIS data and are within positivity constraints. Each flavor is done separately and the overall set can be used to predict polarization asymmetries for various processes. We perform our NLO analysis strictly in x space, avoiding difficulties in moment inversion.Small-x results and other physical considerations are discussed.

We present models for the spin-weighted quark and gluon distribution in a longitudinally polarized proton. The models embody different underlying concepts concerning the application of spindependent forces in the nonperturbative or "soft" regime of chromodynamics. The different spin densities are used to investigate a possible long-range experimental program for measuring various hard-scattering processes using polarized protons. I. INTRODUCI'IONThe measurement of spin-related observables in processes involving polarized protons provides an outstanding opportunity to enhance our knowledge of chromodynamics. Within the framework of the QCD-aided parton model, the well-known spin structure of various hard-scattering subprocesses can be used to probe correlation between the proton spin and the spin of its constituents. Several have provided phenomenological estimates for spin-weighted inclusive scattering processes based on simple models for the parton spin densities. Until recently, however, little attention had been devoted to the question of what a measurement of a spinweighted parton distribution tells us about proton structure.The situation has now changed dramatically. The measurement of the longitudinal spin-spin asymmetry in deep-inelastic leptoproduction5 has recently been extended to small values of the Bjorken-x variable by the European Muon collaboration6 (EMC). The EMC results suggest a strong negative polarization for the sea of qq pairs and have generated a spate of theoretical papers.7-13 The theoretical attention serves to emphasize the importance of understanding how the angular momentum of the proton is shared among the spin of its constituents and orbital angular momentum.The polarization of the gluons in a longitudinally polarized proton has received particular attention. Many of the possibilities discussed theoretically raise new experimental possibilities. I t now becomes important to assign a high priority to a comprehensive experimental program involving polarized protons aimed at answering the many questions raised by these new results.We would like to discuss the information gleamed from the E M C experiment in terms of a future experimental program aimed at separately determining the polarization of the valence quarks, the gluons, and the sea. In planning a new generation of spin-asymmetry experiments, it is useful to have available models for the spin transfer densities which encompass a reasonable range of variation. These models will allow experimenters to assess the precision required to extract the necessary information. For this purpose we have constructed simple model distributions which represent different theoretical scenarios. We have used existing leptoproduction data plus some simple assumptions to constrain the distribution functions. DefinitionsAt this point it is useful to establish our conventions and to introduce the specific definitions we will use for the spin-weighted quark and gluon distributions.We will initially adopt a process-independent set of definitions for the...

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