JLab E07-011: Precision measurements of g1d using ND3 and LiD

We plan to make definitive measurements of the deuteron spin structure function g1d/F1d in the deep-inelastic kinematics accessible with a 6 GeV beam at JLab. The principal goal is to provide the low Q2 anchor points for NLO pQCD plus higher twist fits to g1d/F1d, which is particularly sensitive to ΔG(x)(the polarized gluon density of the nucleon) and the sum of up and down quark polarizations. By spanning a factor of typically two in the Q2-range at nine values of x, the new data will strongly constrain the higher twist contribution to the fits, with a corresponding reduction in the polarized PDF uncertainties. The proposed measurements, when combined with existing and planned world data at higher Q2, will provide the theoretically cleanest determination of ΔG(x) in the moderate to high x region, and will provide a necessary complement to the low x program of RHIC-spin.The experiment will use both 6LiD and ND3 as a source of polarized deuterons, with approximately equal running times for both to constrain the nuclear effects in 6LiD, the target used by the higher Q2 experiments at SLAC and CERN. Both the target and low current (nA scale) 6 GeV electron beam will be longitudinally polarized. Electrons scattered at angles from about 18 deg. to 45 deg. will be detected. Additional measurements at lower Q2 will be made using a 4.8 GeV beam energy.