Psu/th/118 Spin in Perturbative Qcd; Coherent Hard Diffraction 1

I briefly review: (a) some recent developments in the theory of hard scattering in QCD with polarized beams, and (b) coherent hard diffraction (that is, hard scattering in diffractive events, with the Pomeron behaving in an apparently point-like fashion). 1. Polarized Hard Scattering Interest in polarized hard scattering has increased recently. An important reason is that it appears feasible to use polarized protons in the Relativistic Heavy Ion Collider at Brookhaven[1]. The aim is an energy of 200+200 GeV at a luminosity of 2 × 10 cm s and a polarization of 70% for each beam. So the theoretical study of polarization in perturbative QCD is no longer academic. Polarized hard scattering probes the spin-dependence, and hence the chiral properties, of both the proton wave function and quark fragmentation, as is particularly evident in recent work. Rather intriguing are the measurements of spin asymmetries in pion production at large xT in collisions of transversely polarized protons with unpolarized hadrons. Leading twist QCD predicts no asymmetry, so the large measured asymmetries[2] indicate large higher twist effects.