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

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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

Absolute cross sections as functions of kinematic variables are presented for the production of muon pairs from 800 GeV proton bombardment of 'H. Drell-Yan (continuum) dimuons were recorded in the mass regions 4.5 5 M,+,-5 9 GeV and M , -, 2 11 GeV, with an x-Feynman range -0.1 5 X F < 0.75. This range corresponds to smaller masses and larger values of X F than previous 800 GeV Drell-Yan data. Cross sections for the T (IS) resonance are also given versus the transverse momentum and X F . PACS number(s): 13.85.Qk, 12.38.Qk, 25.40.Ve

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The (m+, m ) and (m. , m ) reactions were studied on a variety of nuclei at a bombarding energy of 160 MeV. The full m energy spectra were measured with a m spectrometer at several detection angles. The energy spectra and angular distributions are characteristic of quasifree reactions. Effects due to multiple scattering, neutron screening, and Pauli blocking are clearly observed.