SOME TESTS FOR THE HELICITY STRUCTURE OF THE POMERON IN ep COLLISIONS

We discuss the reaction ep → ep̃X in the one-photon exchange approximation, where it is in essence the reaction γ∗p → p̃X. A large rapidity gap is required between the particle or particles of the proton remnant p̃ and those of X. We define a suitable azimuthal angle φ between a leptonic and a hadronic plane. The dependence of the cross section on φ is given explicitly and can be used to extract cross sections and interference terms for the reaction γ∗p → p̃X corresponding to the various helicities of the virtual photon γ∗. The interference terms can be used to test models for the large rapidity gap events in a sensitive way. We discuss in detail models with factorizing Pomeron exchange and in particular the Donnachie-Landshoff Pomeron model. We make some remarks on soft colour exchange models and on possible effects of QCD background vacuum fields. We conclude with a suggestion to look for Odderon exchange in exclusive deep inelastic high energy reactions like γ∗p → p̃π0 and γ∗p → p̃η.