High-energy Hadron-induced Dilepton Production from Nucleons and Nuclei

We review the production of high-mass lepton pairs in fixed-target experiments, including both Drell-Yan (DY) and heavy quarkonium production (J/ψ, ψ, Υ(1S), Υ(2S), and Υ(3S)). In recent years DY data has become standard input to the determination of parton density distributions. DY data has recently yielded the first measurement of the x-dependence of the d̄/ū asymmetry of the proton. Similar to the observations in deeply inelastic scattering, precision measurements of the nuclear dependence of the proton-induced DY process exhibit shadowing at small target momentum fraction, x2. There is, however, no evidence of enhanced DY production from nuclear targets. Mean transverse momenta of DY pairs is observed to increase with target mass. These data, analyzed within a new theoretical framework, provides an estimation of the energy loss of fast quarks in nuclear matter. In contrast to the DY process, there are large nuclear effects in the production of all quarkonia. These effects show strong dependence on pt and xF , but do not scale with x2. Statistically less precise measurements of D meson (open-charm) production at small xF are consistent with no nuclear dependence.