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The inclusive production cross sections of the strange vector mesons K * 0 , K * 0 , and φ have been measured in interactions of 920 GeV protons with C, Ti, and W targets with the HERA-B detector at the HERA storage ring. Differential cross sections as a function of rapidity and transverse momentum have been measured in the central rapidity region and for transverse momenta up to pT = 3.5 GeV/c. The atomic number dependence is parametrised as σpA = σpN * A α , where σpN is the proton-nucleon cross section. Within the phase space accessible, α(K * 0) = 0.86 ± 0.03, α(K * 0) = 0.87 ± 0.03, and α(φ) = 0.96 ± 0.02. The total proton-nucleon cross sections, determined by extrapolating the differential measurements to full phase space, are σ pN→K * 0 = (5.06 ± 0.54) mb, σ pN→K * 0 = (4.02 ± 0.45) mb, and σ pN→φ = (1.17 ± 0.11) mb. For all resonances the Cronin effect is observed; compared to the measurements of Cronin et al. for K ± mesons, the measured values of α for φ mesons coincide with those of K + mesons for all transverse momenta, while the enhancement for K * 0 /K * 0 mesons is smaller.

The HERA-B RICH uses a radiation path length of 2.8 m in C 4 F 10 gas and a large 24 m 2 spherical mirror for imagingČerenkov rings. The photon detector consists of 2240 Hamamatsu multi-anode photomultipliers with about 27,000 channels. A 2:1 reducing two-lens telescope in front of each PMT increases the sensitive area at the expense of increased pixel size, resulting in a contribution to the resolution which roughly matches that of dispersion. The counter was completed in January of 1999, and its performance has been steady and reliable over the years it has been in operation. The design performance of the RICH was fully reached: the average number of detected photons in the RICH for a β = 1 particle was found to be 33 with a single hit resolution of 0.7 mrad and 1 mrad in the fine and coarse granularity regions, respectively.

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