Enhancement effects in exclusive $\pi \pi$ and $\rho \pi$ production in ${\gamma }^{\ast }\gamma$ scattering

Abstract

The exclusive $\pi \pi$ and $\rho \pi$ production in hard ${\gamma }^{\ast }\gamma$ scattering in the forward kinematical region where the virtual photon is highly off-shell is studied using the $\gamma \to {\pi }^{-}$ Transition Distribution Amplitudes obtained in realistic models for the pion. For $\rho \pi$ production we confirm the previous estimates before QCD evolution. Nevertheless, once evolution is taken into account this cross section grows one order of magnitude. In the case of $\pi \pi$ production we have evaluated the cross section including the pion pole contribution. We observe that this contribution is responsible for an enhancement of two orders of magnitude with respect to the cross section evaluated without the pion pole term.

Comments: Corrected typos, version accepted for publication in Phys. Lett. B