Exclusive production of pion pairs in γ*γ collisions at large Q2

Abstract

We perform a QCD analysis of the exclusive production of two mesons in ${\mathrm{\ensuremath{\gamma}}}^{\mathrm{*}}$\ensuremath{\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 ${\ensuremath{\gamma}}^{*}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}q\overline{q}$ or ${\ensuremath{\gamma}}^{*}\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\gamma}}\mathrm{gg}$ and a generalized two-meson distribution amplitude. We develop in detail the phenomenology of this process at ${e}^{+}{e}^{\ensuremath{-}}$ 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 CERN LEP.