Single spin asymmetries in $\gamma^* \gamma \to \pi \pi \pi$ at large Q^2

Abstract

The $\gamma^* \gamma \to \pi \pi \pi$ reaction is analysed in QCD at large photon virtuality Q and small hadronic mass W. Its amplitude factorizes in a $3 \pi$ generalized distribution amplitude and a hard subprocess $\gamma^* \gamma \to q \bar q$ or $\gamma^* \gamma \to g g$. The interference of this process with a Brehmsstrahlung process in e e or $e \gamma$ collisions gives rise to interesting single spin asymmetries, particularly when W is near the $\omega$ mass.