Hard Scattering in Qcd

Recent developments in the theory and experiment of QCD hard scattering are described. 1 Preamble: How Perturbative QCD Works This has been an active year for experimental results and theoretical developments in quantum chromodynamics. In this talk I will cover a selection of topics presented at this conference, tied together by the interplay of soft and hard physics. QCD is certainly the most complex component of the standard model at current energy scales, evolving as it does from an asymptotically-free perturbative theory of quarks and gluons at short distances to a confining theory of hadrons at long distances. As experiment and theory become more precise, it becomes both possible and necessary to explore the relations between these two limits. I begin with a short review of how we employ the simplicity of the theory at short distances even in the presence of nonperturbative low-energy dynamics. Thus, let us recall a few recurring themes in QCD theory. [1] Infrared Safety. Our first observation is that there is a class of high-energy cross sections and decay rates that may be calculated directly in perturbation theory. These “infrared safe” Presented at the 28th International Conference on High Energy Physics, July 1996, Warsaw, Poland.