Laser-plasma accelerator group

Abstract:

Photon proton cross sections for elastic light vector meson production, σel^νp, inelastic diffractive production, σnd^νp, non-diffractive production, σd^νp, as well as the total cross section, σtot^νp, have been measured at an average υp center of mass energy of 180 GeV with the ZEUS detector at HERA. The resulting values are σel^νp = 18 ± 7 μb, σd^νp = 33 ± 8 μb, σnd^νp = 91 ± 11 μb, and σtot^νp 143 ± 17 μb, where the errors include statistical and systematic errors added in quadrature. © 1994 Springer-Verlag.

Abstract:

Events with a large rapidity gap in deep inelastic scattering with Q2 ≥ 10 GeV2 have been studied in the ZEUS detector. The properties of these events with W > 140 GeV are consistent with a leading twist diffractive production mechanism. In the laboratory frame, with ETjet ≥ 4 GeV, 15% of the events are of the 1-jet type with negligible 2-jet production. The single jet is back-to-back in azimuth with the scattered electron. No energy flow is observed between the jet and the proton direction. With a lower jet transverse energy cut 2-jet production is observed both in the laboratory and the γ* p centre-of-mass systems, demonstrating the presence of hard scattering in the virtual photon proton interactions that give rise to large rapidity gap events. © 1994.

Abstract:

Jets in photoproduction events have been studied with the ZEUS detector for γp centre-of-mass energies ranging from 130 to 250 GeV. The inclusive jet distributions give evidence for the dominance of resolved photon interactions. In the di-jet sample the direct processes are for the first time clearly isolated. Di-jet cross sections for the resolved and direct processes are given in a restricted kinematic range. © 1994.