Exclusive production of pion pairs in gamma^* gamma collisions at large   Q^2
  We perform a QCD analysis of the exclusive production of two mesons in gamma^* gamma collisions in the kinematical domain of large photon virtuality Q and small hadronic invariant mass W. This reaction is dominated by a scale invariant mechanism which factorizes into a perturbative subprocess, gamma^* gamma --> q qbar or gamma^* gamma --> g g, and a generalized two-meson distribution amplitude. We develop in detail the phenomenology of this process at e^+ e^- colliders. Using a simple model for the two-pion distribution amplitude, based on its general properties, we estimate the cross section for the kinematics accessible at BABAR, BELLE, CLEO and LEP. 
Markus Diehl, Thierry Gousset and Bernard Pire