QCD PHYSICS OPPORTUNITIES IN LOW-ENERGY ELECTRON-POSITRON ANNIHILATION

I survey a number of interesting tests of quantum chromodynamics at theamplitude level which can be carried out in electron-positron annihilation andin photon-photon collisions at low energy, including measurements offundamental processes such as timelike form factors and transition amplitudes,timelike Compton scattering, timelike photon to meson transition amplitudes,and two-photon exclusive processes. Many of these reactions test basicprinciples of QCD such as hadronization at the amplitude level, factorization,and hadron helicity conservation, tools also used in the analysis of exclusive$B$ and $D$ decays. Measurements of the final-state polarization in hadron pairproduction determine the relative phase of the timelike form factors. The roleof two-photon exchange amplitudes can be tested using the charge asymmetry ofthe $e^+ e^- \to B \bar B$ processes. Precision measurements of theelectron-positron annihilation cross section can test the generalized Crewtherrelation and determine whether the effective couplings defined from physicalmeasurements show infrared fixed-point and near conformal behavior. I alsodiscuss a number of tests of novel QCD phenomena accessible in $e^+ e^-$annihilation, including near-threshold reactions, the production of baryonium,gluonium states, and pentaquarks.