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HK: Hadronen und Kerne
HK 32: Structure of Baryons, Mesons IV, HERMES, CHORUS, SELEX
HK 32.4: Talk
Tuesday, March 17, 1998, 14:45–15:00, H
Diffractive vector meson production at HERMES — •M. Kolstein and J.J. van Hunen — NIKHEF, P.O. Box 41882, 1009 DB Amsterdam, The Netherlands (for the HERMES Collaboration)
Diffractive ρ0-production data have been collected on 1,2H, 3He and 14N by the HERMES collaboration at DESY. The data are used to measure absolute cross sections, decay-angular distributions and the nuclear transparency. Smaller samples of diffractive ω, φ and J/Ψ events were reconstructed as well. The resulting diffractive ρ0-production cross-sections cover a Q2-range from 0.2 to 5 (GeV/c)2, and might thus resolve a possible descrepancy between existing NMC and E665 data.
The decay-angular distributions provide information on the longitudinal polarisation of the ρ0 meson. Such measurements can be used to investigate the validity of S-channel helicity conservation (SCHC) in ρ0 production, which is not required to be valid in pQCD while it is used as an assumption in VMD-models. Moreover, the nuclear transparency measurements may give evidence of the predicted Color-Transparency phenomenon.
A selection of (preliminary) HERMES data will be presented. As an example, we mention the measured Q2-dependence of the nuclear transparency on 3He. These data are discussed in relation to similar observations reported by the E665 collaboration, and calculations that include both Color-Transparency and coherence-length effects.