Double diffraction dissociation at large momentum transfer

• Main Author: Cox, Brian
• Published: University of Manchester 1998
• Subjects: 531
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.675409

Photoproduction events which have two or more jets with transverse energy ET > 4.5 GeV have been studied in the γp centre of mass energy range 158 GeV < W < 247 GeV with the H1 detector at HERA. The fraction f(Δη) of events with a rapidity gap between the two highest ET jets is measured as a function of the rapidity separation Δη between the jet axes. A gap is defined as the absence between the jets of any particle with energy E > 400 MeV. The gap fraction is observed to fall exponentially up to Δη < 3.5. An excess of events with a large rapidity gap, over what would be expected from standard photoproduction processes, is observed for Δη > 3.5. 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 diffraction at high momentum transfer is presented in which the double dissociation process γp → 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 dσ/dx_p, where x_p = (M²ₓ - t)/W², allows a direct determination of the energy dependence of the diffractive process, and hence provides a stringent test of theories of high |t| diffraction. The double dissociation photoproduction cross section for the process γp → XY is measured for the first time at large 4-momentum transfer squared |t|. > 20GeV² using the H1 detector at HERA. Cross sections are measured differentially in x_p, for yp = (M²_y-t)/W² < 0.018 . In the range 0.0007 < x_p < 0.0040, the shape of the measured x_p 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 |t|.