Some tests for the helicity structure of the pomeron in $ep$ collisions

Abstract

We discuss the reaction $ep\to e\tilde{p}X$ in the one-photon exchange approximation, where it is in essence the reaction ${\gamma }^{\ast }p\to \tilde{p}X$. A large rapidity gap is required between the particle or particles of the proton remnant $\tilde{p}$ and those of $X$. We define a suitable azimuthal angle $\phi$ between a leptonic and a hadronic plane. The dependence of the cross section on $\phi$ is given explicitly and can be used to extract cross sections and interference terms for the reaction ${\gamma }^{\ast }p\to \tilde{p}X$ corresponding to the various helicities of the virtual photon ${\gamma }^{\ast }$. 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 ${\gamma }^{\ast }p\to \tilde{p}{\pi }^0$ and ${\gamma }^{\ast }p\to \tilde{p}\eta$.

Comments: 45 pages (LaTeX), 7 figures as separate postscript files