Odderon and photon exchange in pseudoscalar meson production

Abstract

We consider exclusive $\pi^0$ production in ep-scattering. At high energies odderon and photon exchange contribute. The photon exchange contribution is evaluated exactly using data for the total virtual photon-proton absorption cross section. The odderon exchange contribution is calculated in nonperturbative QCD, using functional integral techniques and the model of the stochastic vacuum. For the proton we assume a quark-diquark structure as suggested by the small odderon amplitude in pp and $p \bar{p}$ forward scattering. We show that odderon exchange leads to a much larger inelastic than elastic $\pi^0$ production cross section. Observing our process at HERA would establish the soft odderon.