Eur. Phys. J. C 25, 169-187 (2002)
DOI: 10.1007/s10052-002-01003-1

Measurement of the Q² and energy dependence of diffractive interactions at HERA

The ZEUS Collaboration

(Received: 27 March 2002 / Published online: 9 August 2002 )

Abstract
Diffractive dissociation of virtual photons, , has been studied in ep interactions with the ZEUS detector at HERA. The data cover photon virtualities 0.17 < Q²< 0.70 GeV ² and 3 < Q²< 80  GeV ² with 3<M_X<38 GeV, where M_X is the mass of the hadronic final state. Diffractive events were selected by two methods: the first required the detection of the scattered proton in the ZEUS leading proton spectrometer (LPS); the second was based on the distribution of M_X. The integrated luminosities of the low- and high- Q² samples used in the LPS-based analysis are  pb ^-1 and  pb ^-1, respectively. The sample used for the M_X-based analysis corresponds to an integrated luminosity of  pb ^-1. The dependence of the diffractive cross section on W, the virtual photon-proton centre-of-mass energy, and on Q² is studied. In the low- Q² range, the energy dependence is compatible with Regge theory and is used to determine the intercept of the Pomeron trajectory. The W dependence of the diffractive cross section exhibits no significant change from the low- Q² to the high- Q² region. In the low- Q² range, little Q² dependence is found, a significantly different behaviour from the rapidly falling cross section measured for Q² > 3 GeV ². The ratio of the diffractive to the virtual photon-proton total cross section is studied as a function of W and Q². Comparisons are made with a model based on perturbative QCD.

© Società Italiana di Fisica, Springer-Verlag 2002