Production of the Smallest QED Atom: True Muonium (mu^+ mu^-)

The "true muonium" (mu^+ mu-) and "true tauonium" (tau^+ tau^-) bound states are not only the heaviest, but also the most compact pure QED systems. The rapid weak decay of the tau makes the observation of true tauonium difficult. However, as we show, the production and study of true muonium is possible at modern electron-positron colliders.