The conventional picture of the proton is based on three "valence" quarks -- two "up" and one "down". This picture has done a remarkable job of describing many properties of the proton. However, thanks to the richness of QCD, the proton is a much more complicated object. In addition to the valence quarks, the proton contains a "sea" of quark-antiquark pairs and gluons that bind the system together. Experiments have been able to explore and map the sea quark distributions, but reconciling this data with a model for the origin of the sea is difficult. The Drell-Yan mechanism provides a tool that can select only the antiquark distributions in the target, making it an ideal process with which to study the sea. Using Drell-Yan, a remarkable asymmetry has been observed in the difference of anti-down to anti-up quarks in the proton. This asymmetry cannot simply be generated through perturbative QCD, but rather indicates an underlying and fundamental antiquark component in the proton. The Fermilab E-906 Drell-Yan experiment will extend earlier measurements of this difference to larger values of xBj and increase statistical precision at lower xBj. To accomplish this goal, a reconfiguration of earlier Drell-Yan experiments is underway. The collaboration expects to begin data collection summer, 2010.
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