Tests of quantum chromodynamics in two-photon collisions and high-pTphoton production

Abstract

We use the diagrammatic approach to scale breaking to rederive the results of the renormalization-group approach to two-photon, ${\ensuremath{\gamma}}^{*}\ensuremath{\gamma}$, 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 ${G}_{\frac{q}{\ensuremath{\gamma}}}({q}^{2},x)=[\frac{\ensuremath{\alpha}}{{\ensuremath{\alpha}}_{s}({q}^{2})}]{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{f}}_{q}(x)+O(1)$, where ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{f}}_{q}(x)$ 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 ${G}_{\frac{q}{\ensuremath{\gamma}}}$ 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 $x\ensuremath{\rightarrow}1$ behaviors.