A precise measurement of the atomic-mass dependence of dimuon production induced by 800-GeV protons is reported. Over 450 000 muon pairs with dimuon mass M≥4 GeV were recorded from targets of H2, C, Ca, Fe, and W. The ratio of dimuon yield per nucleon for nuclei versus H2, R=YA/Y2H, is sensitive to modifications of the antiquark sea in nuclei. No nuclear dependence of this ratio is observed over the range of target-quark momentum fraction 0.1<xt<0.3. For xt<0.1 the ratio is slightly less than unity for the heavy nuclei. These results are compared with predictions of models of the European Muon Collaboration effect.
The yields of the 1S and the sum of the 2S and 3S Υ resonances have been measured for 800-GeV protons incident on targets of H2, C, Ca, Fe, and W. A significant nuclear dependence is seen in the yield per nucleon which, within errors, is the same for the Υ(1S) and Υ(2S+3D) states. A large decrease in the relative yield from heavy nuclei is found for the range xF<0. Significant nuclear dependence is also observed in the pt distribution. Differential cross sections for the Υ(1S) for H2 are presented over the ranges 0.24≤pt≤3.4 GeV/c and -0.15≤xF≤0.5.
The yield of J/ψ and ψ’ vector-meson states has been measured for 800-GeV protons incident on deuterium, carbon, calcium, iron, and tungsten targets. A depletion of the yield per nucleon from heavy nuclei is observed for both J/ψ and ψ’ production. This depletion exhibits a strong dependence on xF and pt. Within experimental errors the depletion is the same for the J/ψ and the ψ’.
The nuclear dependence for 800 GeV/c proton production of neutron D mesons has been measured near xF=0 in Experiment 789 at Fermilab. D mesons from beryllium and gold targets were detected with a pair spectrometer and a silicon vertex detector via their decay D→Kπ. No nuclear dependence is found, with a measured α=1.02±0.03±0.02. The measured differential cross section, dσ/dxF, for neutral-D-meson production at 〈xF〉=0.031 is 58±3±7 μb/nucleon. The integrated cross section obtained by extrapolation of the measured cross section to all xF is 17.7±0.9±3.4 μb/nucleon and is consistent with previous measurements.
In a beam-dump experiment at Fermilab the cross section for charm-particle production has been deduced from a measurement of the prompt neutrino flux. The reaction cross section, if we assume only DD¯ and the dependence on atomic weight A0.75, is 57.2 ± 2.9 ± 8.5 μb/nucleon and the dependence on Feynman x and transverse momentum is EDd3σdpD3∝(1−x)3.2e−1.5p⊥ (p⊥ in GeV/c). The data are consistent with as much as 40% diffractive production of ΛcD¯.
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