Data are presented on exclusive ρ0 and ϕ production in deep inelastic muon scattering from a target consisting mainly of nitrogen. The ratio of the total cross sections for ρ0 and ϕ production is found to be 9∶(1.6±0.4) at 〈Q2〉=7.5 GeV2, consistent with theSU(3) prediction of 9∶2. Thet dependence for exclusive ρ0 production is found to become shallover asQ2 increases and, for largeQ2, thet dependence is typical of that for a hard scattering process. Furthermore, the ratio of the cross sections for coherent: incoherent production from nitrogen is found to decrease rapidly withQ2. Such behaviour indicates that even for exclusive vector meson production the virtual photon behaves predominantly as an electromagnetic probe.
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Exclusive ϱ 0 production has been measured in 120, 200 and 280 GeV muon-proton interactions at high Q 2 (1 GeV 2 < Q 2 < 25 GeV 2 ) and W (6 GeV < W < 19 GeV). The photoproduction cross section decreases as 1/ Q 4 . A shallow t distribution, typical of a hard scattering process is observed and the ϱ 0 is found to be dominantly in the helicity zero spin state. The ϱ 0 s are mainly produced by transverse photons and s -channel helicity conservation seems to be invalid. The data cannot be described by the vector meson dominance model. These data show that at high Q 2 even exclusive ϱ 0 muoproduction is a hard scattering process and that the soft hadron-like properties of the photon have disappeared.
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SYSTEMATIC ERROR ON SLOPE IN 0.8.