Determining the Light Antiquark Asymmetry in the Nucleon Sea with FNAL E-906/SeaQuest*

SeaQuest will use the Drell-Yan process to improve our knowledge of the structure of the nucleon. This experiment will determine the ratio of anti-down to anti-up quarks to larger Bjorken-x than was attained by earlier experiments. SeaQuest's predecessor, Fermilab E-866/NuSea extracted the ratio to x $\approx$ .2 with reasonable precision. SeaQuest will extend the measurements of light antiquark asymmetry to x $\approx$ 0.45. SeaQuest will use the Fermilab 120 GeV/c Main Injector to collide protons with targets of liquid hydrogen, liquid deuterium and, for other measurements, solid nuclear targets. The detector under construction is a two-magnet, focusing spectrometer with four detector stations, similar to the E866/NuSea spectrometer. By comparing the Drell-Yan di-muon cross sections for both proton- proton and proton-deuterium collisions, we can extract $\bar {d}$/$\bar{u}$ for the proton and better understand the properties of the sea of the nucleon.