A precision measurement of the A-dependence of dimuon production in proton-nucleus collisions at 800 GeV/c

Precision measurements of the A-dependence of the reaction p + A → μ⁺μ⁻ + X at 800 GeV/c are reported in this thesis. Data were taken at Fermilab (E772) using a modified version of the large dimuon spectrometer in the Meson-East beamline. A total of 6 × 10⁵ muon pairs were recorded for targets of D, C, Ca, Fe, and W. The kinematic region spanned by the data corresponds to a dimuon invariant mass of 3 ≤ M_μ⁺μ⁻ ≤ 14 GeV, a Feynman-x of -0.1 ≤ x_F ≤ 0.7, and a target parton momentum fraction of 0.03 ≤ x₂ ≤ 0.30. Accurate relative target normalizations were achieved by careful monitoring of beam intensity and position, cyclic interchanges of targets, maintaining nearly 100% electronic livetime, and by use of precisely fabricated targets. The systematic errors in the relative yields are less than 2% for all targets.

Results are presented on the ratios of cross sections for nuclear targets relative to deuterium for the Drell-Yan process and for the production of the J/Ψ,Ψ′, and Υ quarkonia. These ratios are presented as functions of variables P_T and x_F, and versus x₁ and x₂ for the Drell-Yan process. Nuclear depletion at low-x₂ is observed for the first time in the Drell-Ya n process. No nuclear enhancement of the antiquark distribution is observed in the region x₂ ≥ 0.1. The data give tight constraints on models developed to explain nuclear medium effects in deep inelastic lepton scattering (EMC effect). Specifically, published models that have postulated a pion excess and 6-quark clusters are ruled out. The A-dependent behaviors on x_F and P_T for J/Ψ,Ψ′, and Υ production are also reported and compared with previous experiments. Substantial nuclear depletions are observed in both the x_F and P_T dependence. These depletions increase with increasing x_F, and decrease with increasing P_T.