QCD and Two-Photon Physics

A relatively clean environment and well-understood initial state parton content render e+e− colliding beams experiments ideal for both the qualitative confirmation and quantitative testing of Quantum Chromodynamics. Through the years, a number of seminal discoveries and measurements performed at e+e− colliding beam facilities have served to establish the color-charge-based SU(3) gauge theory hypothesis of QCD as the accepted dynamical model of the strong nuclear interaction. Highlights unique to the e+e− QCD program include the discovery of the gluon gauge quantum at PETRA in 1979, the confirmation of the SU(3) gauge structure of quark-gluon and gluon-gluon vertices at LEP in the early 1990’s, and the precise measurement of the strong coupling constant αS via hadronic observables and τ lepton decay. The study of QCD, and the dynamics of the strong force in general, is expected to provide a significant contribution to the physics program at a high energy e+e− colliding beam facility. The highlights of this program include • the precise determination of the strong coupling αS; • the search for anomalous strong couplings of the top quark; • the study of photon structure; and • The study of strong-interaction dynamics at high √s and fixed t.