TESTS OF QUANTUM CHROMODYNAMICS IN 2-PHOTON COLLISIONS AND HIGH-PT PHOTON PRODUCTION

We use the diagrammatic approach to scale breaking to rederive the results of the renormalization-group approach to two-photon, γ*γ, collisions, where one of the photons is highly virtual and the other nearly real. In an axial gauge only ladder diagrams contribute to leading-logarithmic accuracy. When interpreted in terms of the quark distribution of the real photon we obtain the result Gqγ(q2,x)=[ααs(q2)]fq(x)+O(1), where fq(x) is an exactly calculable scaling function. By virtue of the fact that only ladder diagrams contribute in leading-logarithmic accuracy for this and other short-distance photon-target probes, we find that this form for Gqγ can be employed (to leading-logarithmic accuracy) in any short-distance application involving a photon target. We give a summary of these additional applications with emphasis on high-transverse-momentum phenomena. We present also estimates of the vector-dominance background to the pointlike component of the photon distribution function. In addition we present a convenient summary of leading-logarithmic quantum-chromodynamic corrections including dominant x→1 behaviors. © 1979 The American Physical Society.