Investigation of - and Odderon Induced Photoproduction of Mesons Decaying to Pure Multiphoton Final States at Hera

Cross section measurements made at HERA for the reactions γp → ωp and γp → ωπ⁰X, and on searches for the reactions γp → π⁰ N*, γp → f₂(1270)X, and γ p -> a⁰₂(1320)X, where N* denotes an excited nucleon state, are presented. The mean γp centre-of-mass energies were <W> = 200 GeV and 215 GeV, respectively. Cross sections for the Pomeron-mediated reactions were determined in agreement with previous measurements and phenomenological expectations. In contrast, Odderon induced processes have not been observed; upper limits on cross sections are below predictions from a non-perturbative QCD model.