Exclusive $\eta_c$ photo- and electroproduction at HERA as a possible   probe of the odderon singularity in QCD
  Theory and phenomenology of the eta_c 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 the cross-sections which are independent of W^2 for the exchange of three non-interacting gluons or exhibit increase with increasing W^2 (or 1/x) for the odderon intercept above unity. The \eta_c electroproduction in the three gluon exchange mechanism is shown to be entirely controlled by the transversely polarised virtual photons. The magnitude of the eta_c photoproduction cross-section is estimated to be around 11-45pb. The t-dependence of the differential cross-section is also discussed. 
J. Czyzewski (1), J. Kwiecinski (2), L. Motyka (1), M. Sadzikowski (2)   (1 - Institute of Physics, Jagellonian University, ...