Experiment E1039, polarized SeasQuest

We have constructed a state-of-the-art, high luminosity polarized proton and deuteron target and propose to measure the Sivers asymmetry for the $\bar{u}$ and $\bar{d}$ sea quarks in the nucleon for four different Bjorken $x_B$ bins in the range $0.1 < x_B < 0.5$, using the Drell-Yan process at SeaQuest. We will: i) perform the first measurement of the Sivers asymmetry in Drell-Yan scattering for sea quarks; ii) determine the flavor dependence of the Sivers function for the $\bar{u}$ and $\bar{d}$ sea quarks iii) explore a unique range of virtualities and transverse momenta not accessible through $Z^0/W^\pm$ measurements; and iv) determine the sign and possibly the magnitude of the sea quark Sivers function in Drell-Yan for comparison to future sea quark Sivers function determinations in Semi Inclusive Deep Inelastic Scattering (SIDIS). Measuring a nonzero Sivers asymmetry would provide ``smoking gun'' evidence for nonzero orbital angular momentum of sea quarks; determination of the $\bar{u}$ and $\bar{d}$ Sivers function would allow comparison of the sea quark Sivers function flavor dependence to that for valence quarks; and measuring a sign change in the Sivers asymmetry between this measurement and future measurements at the EIC would test a fundamental prediction of QCD.