Double Di raction Dissociation at Large Momentum Transfer

Photoproduction events which have two or more jets with transverse energy ET GeV have been studied in the p centre of mass energy range GeV W GeV with the H detector at HERA The fraction f of events with a rapidity gap between the two highest ET jets is measured as a function of the rapidity separation between the jet axes A gap is de ned as the absence between the jets of any particle with energy E MeV The gap fraction is observed to fall exponentially up to An excess of events with a large rapidity gap over what would be expected from standard photoproduction processes is observed for The excess can be interpreted as the result of the exchange of a strongly interacting colour singlet object A new approach to the investigation of di raction at high momentum transfer is presented in which the double dissociation process p XY is studied The systems X and Y are separated by the largest rapidity gap in the event with all particles on the photon side of the gap ascribed to the system X It is shown that a measurement of the cross section d dx IP where x IP M X t W allows a direct determination of the energy dependence of the di ractive process and hence provides a stringent test of theories of high jtj di raction The double dissociation photoproduction cross section for the process p XY is measured for the rst time at large momentum transfer squared jtj GeV using the H detector at HERA Cross sections are measured di erentially in x IP for yIP M Y t W In the range xIP the shape of the measured x IP distribution is compared to predictions for standard photoproduction processes and to a model based on the exchange of a strongly interacting colour singlet object at large jtj No portion of the work referred to in this thesis has been submitted in support of an application for another degree or quali cation of this or any other institute of learning Copyright in text of this thesis rests with the author Copies by any process either in full or of extracts may be made only in accordance with instructions given by the author and lodged in the John Rylands University Library of Manchester Details may be obtained from the librarian This page must form part of any such copies made Further copies by any process of copies made in accordance with such in structions may not be made without the permission in writing of the author The ownership of any intellectual property rights which may be described in this thesis is vested in the University of Manchester subject to any prior agreement to the contrary and may not be made available for use by third parties without the written permission of the University of Manchester which will prescribe the terms and conditions of any such agreement Further information on the conditions under which disclosures and exploitation may take place is available from the Head of Department of Physics and Astronomy This work was supported nancially by the Particle Physics and Astronomy Re search Council P P A R C between October and October