We have studied muon pairs with an invariant mass between 4 and 9 Gev/c2 produced in PN and a -N interactions at an incident momentum of 125 GeV/c. The experiment was performed at Fermilab using a tungsten target and a special beam enriched to contain 18% antiprotons. We compare differential distributions as functions of the dimuon invariant mass, Feynman x, transverse momentum, and decay angles of the dimuon to the predictions of the Drell-Yan model including QCD corrections. Quark structure functions for the j7 and n are extracted. Comparisons of the antiproton data to the Drell-Yan model are significant because the cross sections depend principally on the valence-quark structure functions which are accurately determined by deep-inelastic scattering measurements. The measured absolute cross section (integrated over positive Feynman x and all transverse momenta) is 0.106+0.005+0.008 nb/nucleon for the p,V interaction and 0.107+0.003+0.009 nb/nucleon for the n -N interaction, where the quoted errors are statistical and systematic, respectively. Normalization ( K ) factors that are required to bring the naive Drell-Yan and first-order QCD predictions into agreement with the measurements are extracted, and the uncertainties involved in such comparisons are examined.

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The production of the J'IV resonance in 125-GeV/c p and 0 ~ interactions with Be, Cu, and W targets has been measured. The cross section per nucleon for J/y/ production is suppressed in W interactions relative to the lighter targets, especially at large values of Feynman x, which is opposite to the expectation from the various explanations of the European Muon Collaboration effect. Models incorporating modifications of the gluon structure functions in heavy targets show qualitative agreement with the data.

The cross section for the reaction pN^ /x"^/>t"Zwith muon pairs in the mass range 4 < Af < 9 GeV/c^ and Xf>Q was measured to be a-= 0.104 ±0.005 ±0.008 nb/nucleon. The distributions do-/ dxf and M^ da/ dMv^QXQ compared to the QCD-improved Drell-Yan model and to calculations including first-order QCD corrections, with use of deep-inelastic structure functions. Excellent agreement with the data was obtained if the calculations were multiplied by factors of 2.45 and 1.41, respectively.PACS numbers: 13.85.Qk Many predictions of the Drell-Yan model^ for highmass dimuon production by hadrons have been confirmed by measurements with proton and pion beams.^ The integrated polar-angle decay distribution of the muon pairs is consistent with 1-1-cos^^. Scaling in T^M'^IS has been verified in proton-produced data over the energy range (V5^ = 19.4-62 GeV) spanned by Fermilab and the CERN intersecting storage rings. The measured dependence of the cross section on the atomic number of the target is very close to A^-^. These features along with the observation that the ratio of TT"^ to 7r~ dimuon production tends toward x give confidence that high-mass muon-pair production is an electromagnetic process of the type hypothesized by Drell and Yan. However, comparisons of the measured absolute cross sections to the model are more difficult since the predictions for the proton-induced reaction are affected by uncertainties in the nucleonsea structure functions and the pion structure function cannot be measured independently at large Q^. In contrast, data with incident antiprotons can be directly compared to the absolute predictions of the Drell-Yan model since the valence-quark structure function of the nucleon (and hence the valence-antiquark structure functions of the antiproton) have been indepen-dently determined in deep-inelastic lepton scattering (DIS) experiments.^ The present experiment was performed at Fermi National Accelerator Laboratory with a tertiary beam"^ of 1.5X 10'^ particles/sec_and consisting of 18% ^and 82% 77" resulting from A^, A^, and K^ decays. Particle type was determined by two Cherenkov counters resulting in less than 0.5% pion contamination of the antiproton data. Counter hodoscopes and proportional chambers were used to determine the trajectory and momentum of each incident beam particle. Only one experiment^ has previously reported significant p data, but because the antiproton content of the beam was only a few percent of the total flux of 5x10^^ particles/sec, a 25% subtraction for TT" contamination in the ^data sample was required.The experimental spectrometer^ is shown in Fig. 1. It included a tungsten target, a copper hadron absorber (10.3 absorption lengths), twenty proportional-and drift-chamber planes, a large-aperture analysis magnet, an X'Y charged-particle scintillation-counter hodoscope, and a 13.2-absorption-length steel and concrete muon detector with three imbedded muon trigger planes of sixty counters each. Two-thirds of our data were accumulated with a 1.5-absorption-length 2572

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