Rapidity gaps between jets in photoproduction at HERA
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 369:1 (1996) 55-68
Abstract:
Photoproduction events which have two or more jets have been studied in the Wγp range 135 GeV < Wγp < 280 GeV with the ZEUS detector at HERA. A class of events is observed with little hadronic activity between the jets. The jets are separated by pseudorapidity intervals (Δη) of up to four units and have transverse energies greater than 6 GeV. A gap is defined as the absence between the jets of particles with transverse energy greater than 300 MeV. The fraction of events containing a gap is measured as a function of Δη. It decreases exponentially as expected for processes in which colour is exchanged between the jets, up to a value of Δη ∼ 3, then reaches a constant value of about 0.1. The excess above the exponential fall-off can be interpreted as evidence for hard diffractive scattering via a strongly interacting colour singlet object.Inclusive charged particle distributions in deep inelastic scattering events at HERA
Zeitschrift fur Physik C-Particles and Fields 70:1 (1996) 1-15
Abstract:
A measurement of inclusive charged particle distributions in deep inelastic ep scattering for γ*p centre-of-mass energies 75 < W < 175 GeV and momentum transfer squared 10 < Q2 < 160 GeV2 from the ZEUS detector at HERA is presented. The differential charged particle rates in the γ*p centre-of-mass system as a function of the scaled longitudinal momentum, xF, and of the transverse momentum, pt* andMeasurement of the diffractive cross section in deep inelastic scattering
Zeitschrift fur Physik C-Particles and Fields 70:3 (1996) 391-412
Abstract:
Diffractive scattering of γ∗p → X + N, where N is either a proton or a nucleonic system with MN < 4 GeV has been measured in deep inelastic scattering (DIS) at HERA. The cross section was determined by a novel method as a function of the γ∗p c.m. energy W between 60 and 245 GeV and of the mass MX of the system X up to 15 GeV at average Q2 values of 14 and 31 GeV2. The diffractive cross section dσdi f f /dMX is, within errors, found to rise linearly with W. Parameterizing the W dependence by the form dσdi f f /dMX ∞ (W2)(2αIP - 2) the DIS data yield for the pomeron trajectory αIP = 1.23±0.02(stat)±0.04(syst) averaged over t in the measured kinematic range assuming the longitudinal photon contribution to be zero. This value for the pomeron trajectory is substantially larger than αIP extracted from soft interactions. The value of αIP measured in this analysis suggests that a substantial part of the diffractive DIS cross section originates from processes which can be described by perturbative QCD. From the measured diffractive cross sections the diffractive structure function of the proton F2D(3) (β,Q2, xIP) has been determined, where β is the momentum fraction of the struck quark in the pomeron. The form F2D(3) = constant·(1/xIP)a gives a good fit to the data in all β and Q2 intervals with a = 1.46 ± 0.04(stat) ± 0.08(syst).A search for excited fermions in electron-proton collisions at HERA
Zeitschrift für Physik C Particles and Fields 65:4 (1995) 627-647