Search for Odderon Induced Contributions to Exclusive π0 Photoproduction at Hera

A search for contributions from odderon - photon fusion to exclusive single π⁰ production via ep → eπ⁰N* in the photoproduction regime at HERA, at an average photon - proton centre-of-mass energy <W> = 210 GeV, and for photon virtualities of Q² < 0.01 GeV² is reported. The measurement proceeded via detection of the π⁰ decay photons, the leading neutron from the N* decay, and the scattered electron. No indication for an odderon contribution was found. An upper limit is presented for the cross section integrated in the "visible" range 0.02 GeV² < -t < 0.3 GeV². It was derived as σ(γp → π⁰N*) < 39 nb at 95 % CL. This excludes an odderon - photon fusion cross section of 400 nb as predicted by theory.