The interpretation of rapidity gaps at HERA

In leading twist deep inelastic ep scattering, the virtual photon interaction is fast compared to the time scale of soft color rearrangement. We compare the Pomeron exchange model, in which a neutral cluster is preformed, with a gluon exchange model, in which color is exchanged after the hard interaction. We find several features of the DIS data and of data on exclusive hard processes that favor a gluon exchange scenario. If correct, the postulate of soft color interactions between the produced (qq¥) system and the target has important implications for other processes. In particular, this may explain the puzzles of charmonium hadroproduction.