1. Measuring the Spin Structure of 3 He and the Neutron at Low Q 2 Timothy Holmstrom College of William and Mary For the Jefferson Lab Hall A Collaboration DNP 2005 Maui, Hawaii, September 22, 2005

2. Polarized Inclusive Electron Scattering Probe the response of the entire nucleus structure. Provides a way to test QCD. Measures the scattering of all interactions. Dominated by one-photon exchange.

3. Gerasimov-Drell-Hearn Sum Rule Relates the difference between polarized photo- production cross sections of real photons (Q 2 = 0) aligned and anti-aligned with the target’s spin to the anomalous magnetic moment. Has been used in analysis and theoretical predictions. For spin ½ targets it is:

4. The Generalized GDH Integral Extends the GDH Sum Rule to the finite Q 2 region. Allows the comparison of experimentally measured quantities at finite Q 2 s with theoretical predictions. Replaces the photoproduction cross-sections with the electroproduction ones. Related to the forward Compton scattering amplitude (S 1(2) ), which can calculated by theory on full nucleon spectrum.

5. JLab Experiment E94010 Extended GDH integral on the Neutron at intermediate Q 2 (0.1-0.9 GeV 2 ). (PRL 89, 242301-1 (2002)) Used the Hall A HRSs. Polarized 3 He target. An extension from the known region of QCD to the unknown. The lowest Q 2 point compares with chiral perturbation theory calculations.

6. Small Angle GDH (E97110) Precise measurement of the Q 2 dependence of the generalized GDH integral and the moments of the 3 He and neutron spin structure functions between 0.02 to 0.3 GeV 2. Measurement of asymmetries and cross sections will allow us to: –Determine the slope of the extended GDH integral as Q 2 approaches 0. –Test the applicability of Chiral Perturbation at low Q 2. –Extrapolate to the real photon point for 3 He and the Neutron –Constrains the resonance structure of the nucleon. The results will also compliment the e94010 Q 2 results from 0.1 to 0.3 GeV 2 with higher precision. The experiment was run successfully in the spring and summer of 2003 using the right Hall A High Resolution Spectrometer. A new septum magnet was used to measure inclusive electron scattering at 6° and 9°.

7. Jefferson Lab Hall A

8. Polarized 3 He Target The 3 He is polarized through spin exchange with optically pumped Rb atoms. Two methods of polarimetry: NMR and EPR. Target polarization in beam  38.5 . Longitudinal and transverse polarization configurations were used.

9. Kinematics Coverage The integral will be calculated between Q 2 of 0.02GeV 2 and 0.3GeV 2. The high level overlap will allow us the minimal amount of interpellation.

10. Expected Results

11. Elastic Asymmetry Elastic Scattering at 9° with a beam energy of 1.142 GeV. Four different target and beam configurations agree with each other. Preliminary analysis agrees with Monte Carlo predictions.

12. Septum Optics and Acceptance Calculation of the magnetic database including the septum is now complete. Results look good at both 6 ○ and 9 ○. Extensive studies are currently being preformed to understand our acceptance with the septum magnet.

13. Conclusions The low Q 2 GDH experiment was successfully run at Jefferson Lab in the summer of 2003. The experiment will provide new low Q 2 measurements of the extended GDH integral, which will: –check the limits of applicability of Chiral Perturbation Theory –determine where or if the slope turns over, which is important for nucleon structure resonances –allow an extrapolation to the real photon point. The data complements the E94010 data above Q 2 of 0.1 with better precision. Elastic asymmetry analysis looks good The septum optics is complete, and analysis of the acceptance is going well. We hope to have preliminary cross sections by the end of the year.

14. Using 3 He as a Neutron Target 3 He nucleons come in three possible states: S, D, S′. The S State dominates leading to an effective neutron polarization of 86%. (J. Friar et al.).