Exclusive ηc photo- and electroproduction at HERA as a possible probe of the odderon singularity in QCD

Theory and phenomenology of the ηc photo- and electroproduction is developed from the point of view of probing the odderon singularity in QCD which corresponds to the three gluon exchange mechanism. This mechanism leads to cross-sections which are independent of W2 for the exchange of three non-interacting gluons or exhibit an increase with increasing W2 (or 1x) for the odderon intercept above unity. The ηc electroproduction in the three gluon exchange mechanism is shown to be entirely controlled by the transversely polarised virtual photons. The magnitude of the ηc photoproduction cross-section is estimated to be around 100–400 pb. The t-dependence of the differential cross-section is also discussed.