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

We discuss the reaction ep --> <e(p)over tilde X> in the one-photon ex change approximation, where it is in essence the reaction gammap --> (p) over tildeX$. A large rapidity gap is required between the particl e or particles of the proton remnant (p) over tilde and those of X. We define st suitable azimuthal angle phi between a leptonic and a hadro nic plane. The dependence of the cross section on phi is given explici tly and can be used to extract cross sections and interference terms f or the reaction gammap --> (p) over tildeX$ corresponding to the vari ous helicities of the virtual photon gamma. The interference terms ca n be used to test models for the large rapidity gap events in a sensit ive 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 O dderon exchange in exclusive deep inelastic high energy reactions like gammap --> <(p)over tilde pi(0)> and gamma*p --> <(p)over tilde eta> .