RELATING HARD QCD PROCESSES THROUGH UNIVERSALITY OF MASS SINGULARITIES

Hard QCD processes involving final jets are studied and compared by means of a simple approach to mass singularities. This is based on the Lee-Nauenberg-Kinoshita theorem and on a rather subtle use of gauge invariance in hard collinear gluon bremsstrahlung. One-loop results are easily derived for processes involving any number of initial quarks and/or currents. The method greatly simplifies the computation of higher-order loops at the leading log level and our preliminary results allow us to conclude that the crucial features encountered at the one-loop level will persist. We are thus able to relate different hard processes and to show that suitable ratios of cross sections, being free from mass singularities, can be computed perturbatively, as usually assumed in QCD-inspired parton models. We are also able to relate our universal leading mass singularities to leading scaling violations and to extend therefore the results of the operator product expansion method to processes outside the range of the light-cone analysis. Some delicate points caused by confinement-related singularities (e.g., narrow resonance poles) are also discussed. © 1978.