SPIN OBSERVABLES FOR NN-]NN AT LARGE MOMENTUM-TRANSFER

We discuss amplitudes for NN --> NN in the hard-scattering regime. Although our starting point is based on perturbative QCD, we do not attempt a full QCD calculation. Instead, the helicity-conserving amplitudes are modeled using a combination of the quark-interchange and the Landshoff mechanisms. The relative normalization of these two sets of amplitudes involves a "form factor" which (in the absence of a complete higher-order calculation) we determine empirically. Helicity-nonconserving amplitudes are then constructed from the helicity-conserving ones based on the application of covariance arguments to the nucleon wave function. At present, this also involves an undetermined constant. Our theoretically motivated amplitudes provide an economical description of a large body of existing data and make some nontrivial predictions.