2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/46425An excess of events with a rapidity gap between jets, over what would be expected from non-diffractive processes, has been observed at HERA. A process based on a perturbative QCD calculation of colour singlet exchange has been added to HERWIG. With this addition, HERWIG is able to describe the number of events with a gap between jets over the number without a gap. This gap fraction is predicted to rise at large rapidity intervals between jets which would only be visible if the detector coverage were increased.5 pages including 3 figures. To appear in the conference proceedings of the Workshop "Future Physics at HERA"High Energy Physics - Phenomenologytext