Presentation on theme: "The Spin Structure of 3 He and the Neutron at Low Q 2 : A Measurement of the Extended GDH Integral Vincent Sulkosky (for the JLab Hall A Collaboration)"— Presentation transcript:
The Spin Structure of 3 He and the Neutron at Low Q 2 : A Measurement of the Extended GDH Integral Vincent Sulkosky (for the JLab Hall A Collaboration) Jefferson Lab, Newport News, VA Kinematic coverage. Target performance during experiment E Polarized 3 He Target Effective polarized neutron target 3 He as an effective n target: 3 He n 3 He = Target cells: 40 cm, ~ 10 atm Highest polarized luminosity in the world: up to cm -2 s -1 Spin exchange optical pumping between Rb and 3 He. 3 He standard target cell. Polarized RB and 3 He Polarized 3 He only 220 o C 50 o C Special cell designed for forward angle detection. Electron Beam Scattered Electrons Target Apparatus and Performance Polarized target setup. Longitudinally and transversely polarized target. P targ = 39% (preliminary analysis). Two independent polarimetries: NMR and EPR. P He = k w * S He P He * [ 3 He] Expected Results How do PT slopes compare to the new data? Is there a minimum and turnover? E expected accuracy for the neutron generalized GDH integral. The red circles show the E results. The blue circles show the Q 2 range, and the blue band shows the expected systematic uncertainty. The vertical axis has been normalized to the neutron value at the real photon point (233.2 b). 3 He GDH integrand. Analysis and Preliminary Results Analysis Procedure: Measure asymmetries and unpolarized cross sections. Form polarized cross-section differences. Extract structure functions and moments. 3 He spin structure functions. Experimental Overview The goal of Jefferson Lab experiment E is to study neutron and 3 He spin structure by performing a precise measurement of the generalized Gerasimov-Drell-Hearn (GDH) integral at Q 2 between 0.02 and 0.3 GeV 2. The Experiment was run in summer 2003 in Hall A. Experimental Setup Polarized electron beam, average P beam ~ 75% Current ~ 1-10 A Hall A polarized 3 He target (as effective neutron target) Scattered electrons detected by Hall A High Resolution Spectrometer coupled with a septum magnet (inclusive reaction). Septum magnet: horizontal bending dipole magnet that enabled detection of electrons at 6 and 9 degrees. The GDH Experiments at JLab in Hall A GDH Sum Rule (Q 2 = 0) and : cross sections for photoproduction with two different photon polarizations. Anomalous magnetic moment : measure of a particles deviation from point-like behavior. Can be generalized for nonzero Q 2. Sum Rule Static Properties measured theory well known Generalized GDH (Q 2 > 0) Replace photoproduction cross sections with electroproduction (virtual photons). Previous JLab experiment E94-010: Measured generalized GDH on neutron with Q 2 between 0.1 to 0.9 GeV 2. Studied transition between strong interactions partonic to hadronic descriptions. Results did not agree well with Chiral perturbation theory above 0.1 GeV 2. Present work, JLab experiment E97-110: Benchmark check of chiral perturbation theory ( PT) in a region where it should be valid. Extrapolate to the real point (Q 2 = 0).