SeaQuest with a Transversely Polarized Target (E1039)

We have constructed a state-of-the-art, high luminosity polarized proton and deuteron target and propose to measure the Sivers asymmetry for the ū and d̄ sea quarks in the nucleon for four different Bjorken xB bins in the range 0.1 < xB < 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 ū and d̄ sea quarks iii) explore a unique range of virtualities and transverse momenta not accessible through Z0/W± 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 ū and d̄ 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. This proposal seeks funding from DOE Office of Nuclear Physics for the installation of the E-1039 experiment, which could be the beginning of an exciting new spin physics program at Fermilab that is complementary to the spin physics programs at RHIC and JLab.