E97-110: Small Angle GDH Experimental Status Report

1. E97-110: Small Angle GDHExperimental Status Report Vincent Sulkosky Massachusetts Institute of Technology Hall A Collaboration Meeting December 9th, 2010

2. Introduction E97-110 • Precision measurement of the moments of spin structure functions at low Q2, 0.02 to 0.24 GeV2 for the neutron (3He) • Covered an unmeasured region of kinematics to test theoretical calculations (Chiral Perturbation theory) • Complements data from experiment E94-010 covered region from 0.1 to 0.9 GeV2 • Finalizing systematic uncertainties and first publication

3. Neutron Spin Polarizabilities

4. Experiment E97-110 • Inclusive experiment: • Scattering angles of 6◦ and 9◦ • Polarized electron beam: Pbeam= 75% • Pol. 3He target (para & perp): Ptarg = 40% • Measured polarized cross-section differences M. Amarianet al., PRL 89, 242301 (2002)

5. Analysis Status • Preliminary results for the moments have been extracted at constant Q2. • Collimator background is mostly from polarized 3He • Need to estimate size of leakage into physics asymmetry • Issues and analysis still in progress: • Elastic analysis as a cross check of systematics (V. Laine) • Near final target polarizations (J. Singh) Expect to receive final numbers very soon. • Acceptance: very messy but making steady progress • Finalize radiative corrections (J. Singh, T. Holmstrom & V. S.) Have received updated code from J. Singh; documentation and notes expected soon

6. Elastic Asymmetry Analysis Work by V. Laine`

7. Updated SAMC Code • Work done by V. Laine` • SAMC rewritten in C++ from Fortran • Improved implementation of target collimator cuts • Raster correction by calculating electron’s travel length through the cell • Radiative corrections made for each material separately (previously done all at once) • Default units now in meter, gram, GeV and radian instead of cm and mrad

8. 3He Elastic Acceptance Delta ytg W-M

9. Acceptance Issues Septum Mistuned

10. Delta Acceptance E94-010 • Flat region of • -acceptance • is much smaller • with Septum • Simulation is not • perfect on the • falling edges E97-110

11. Solution • ||  3.6% • Removed edge bins with a secondary process • Corrected remaining edge imperfections with a secondary acceptance correction

12. 9-Degree Acceptance • More painful: • Saturation effect is present • A few settings were mistuned with the septum magnet • tg-acceptance appears squeezed at the highest field settings

13. Current Work • Target polarization should be final in about a week (J. Singh) • Elastic 3He analysis (V. Laine) • 2.1 GeV asymmetry mostly complete • Next cross section • Finalize acceptance (V. Sulkosky) • Radiative Corrections • Preliminary done by J. Singh; code now available • Tim Holmstrom has agreed to help • Estimation of QE contribution to neutron results (V. Sulkosky)

14. Summary • Work is progressing though slowly • Acceptance analysis should be wrapping up soon • Major work needs to go into radiative corrections • Finite acceptance for elastic tail subtraction • Need a better technique to smooth the data • Model for the two lowest energies • Draft of first paper in progress and expect to be internally available in January 2011

15. Systematic Uncertainties

16. Kinematic Coverage