A precise measurement of the atomic-mass dependence of dimuon production induced by 800-GeV protons is reported. Over 450000 muon pairs with dimuon mass A/> 4 GeV were recorded from targets of 2 H, C, Ca, Fe, and W. The ratio of dimuon yield per nucleon for nuclei versus 2 H, R ~YA/YI H , 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

No abstract

We report an analysis of the nuclear dependence of the yield of Drell-Yan dimuons from the 800 GeV/c proton bombardment of 2 H, C, Ca, Fe, and W targets. Employing a new formulation of the Drell-Yan process in the rest frame of the nucleus, this analysis examines the effect of initial-state energy loss and shadowing on the nuclear-dependence ratios versus the incident proton's momentum fraction and dimuon effective mass. The resulting energy loss per unit path length is −dE/dz = 2.32 ± 0.52 ± 0.5 GeV/fm. This is the first observation of a nonzero energy loss of partons traveling in nuclear environment.24.85.+p; 13.85.Qk; 25.40.Ve For many years it has been suggested that quark energy loss might give rise to a nuclear dependence [1][2][3][4] of the cross section of Drell-Yan [5] (DY) production. When a proton enters a nucleus the first (soft) inelastic collision liberates a quark, which then loses energy via hadronization (due to confinement) and interaction in the nuclear medium. A lepton pair created from a subsequent interaction then has reduced energy compared with the DY process on a free nucleon. The goal of the present analysis is to search for this effect in the nuclear dependence of the DY process.Fermilab E772 made a precise measurement of the nuclear dependence of the DY process using 800 GeV/c protons. The experimental details of E772 have been described previously [6][7][8]. Briefly we indicate those germane to the present discussion. Muon pairs were recorded from targets of 2 H, C, Ca, Fe, and W, in the mass range M ≥ 4 GeV/c 2 . Excluding the Υ resonance region, 9 ≤ M ≤ 11 GeV/c 2 , we reconstruct 2.5 × 10 5

The yield of J/y/ and y/' 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/y/ and y/ production. This depletion exhibits a strong dependence on XF and p t . Within experimental errors the depletion is the same for the J/y/ and y/\ PACS numbers: 13.85.Ni, 25.40.Ve

We present an analysis of 800-GeV proton-induced Drell-Yan production data from isoscalar (IS) targets ^H and C, and from W, which has a large neutron excess. The ratio of cross sections per nucleon, /?=crw/cJis, is sensitive to the difference between the J(^) and w(x) structure functions of the proton. We find that R is close to unity in the range 0.04 < x < 0.27, allowing upper limits to be set on the 2-u asymmetry. Additionally, the shape of the differential cross section m^d^Gldxpdm for ^H at Xf ^==0 shows no evidence of an asymmetric sea in the proton. We examine the implications of these data for various models of the violation of the Gottfried sum rule in deep-inelastic lepton scattering.PACS numbers: I3.85.Qk, 12.38.Qk, 24.85.+p, 25.40.Ve Recent precise measurements by the New Muon Collaboration (NMC) [1] of the Fi structure function in deep-inelastic muon scattering (DIS) from hydrogen and deuterium targets show that