Search for Odderon induced contributions to exclusive Meson Photoproduction at HERA ∗

Odderon induced contributions to exclusive photoproduction of π • , f 2 (1270) and a 2 (1320) have been searched for at HERA, using the multiphoton decays of these mesons. No indication for such contributions was found, in a kinematic region defined by the average photon-proton centre-of-mass energy W = 200 − 215 GeV, photon virtual-ities Q 2 < 0.01 GeV 2 and 0.02 GeV 2 < |t| < 0.3 GeV 2 , where t is the squared momentum transfer at the proton vertex. The measured upper limits for the cross sections, σ(γp → O π • N *) < 39 nb, σ(γp → O f 2 (1270)X) < 16 nb and σ(γp → O a 2 (1320)X) < 96 nb, all at 95 % CL, are lower than the predictions by a theoretical model. Exclusive photoproduction of ω and ωπ • , in the 3γ and 5γ decay modes, is observed with the expected cross sections.