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E97-110: Small Angle GDH Experimental Status Report

E97-110: Small Angle GDH Experimental Status Report. Vincent Sulkosky Massachusetts Institute of Technology Hall A Collaboration Meeting December 15 th , 2011. Motivation.

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E97-110: Small Angle GDH Experimental Status Report

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  1. E97-110: Small Angle GDHExperimental Status Report Vincent Sulkosky Massachusetts Institute of Technology Hall A Collaboration Meeting December 15th, 2011

  2. Motivation • 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. E97-110 Spin Polarizabilities

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

  6. Current Work • Waiting on final target polarization (J. Singh) • Elastic 3He analysis (V. Laine) • 2.1 GeV asymmetry and cross section completed • Now working on 2.8 GeV data set • Finalize acceptance (V. Sulkosky) • Radiative Corrections • Preliminary done by J. Singh; code now available • Tim Holmstrom working on it • Estimation of QE contribution to neutron results (V. Sulkosky)

  7. 9o Acceptance • Difficulty: • Saturation effect is present • A few settings were mistuned with the septum magnet • tg-acceptance appears squeezed at the highest field settings • Varying acceptance cuts does not help Septum Mistuned 15% uncertainty

  8. Interpolation • ||  3.6% • Removed edge bins with a secondary process • Corrected remaining edge imperfections with • a secondary acceptance correction • The interpolation method works, but there is a concern • about the adjacent momentum settings. • Carbon cross section analysisto verify the absolute • normalization of the data.

  9. Tools for Carbon Cross Sections • Single carbon foil data were taken for each of the momentum settings for E = 3.775 GeV • Single Arm Monte-Carlo (SAMC) from A. Deur • Uses John LeRose transport functions at 9º and apertures • Program complied with QFS subroutines to perform radiative corrections: internal and external • Program utilizes the parameterized cross section for A> 2 from P. Bosted: https://userweb.jlab.org/~bosted/F1F209.f • Elastic radiative tail was removed using Rosetail averaged over the solid angle acceptance of E97-110

  10. Septum Entrance Apertures • Shift large angle side • by 7mm • Shift small angle side • by 5 mm

  11. Carbon Cross Section 2.007 GeV/c

  12. Carbon inelastic cross sections

  13. Summary • Work is progressing • Acceptance analysis to be completed soon • More work needs to go into radiative corrections: • Smoothing of the data completed (T. Holmstrom) • Finite acceptance for elastic tail subtraction • Model for the two lowest energies • Draft of first paper completed and internally circulated

  14. Radiative Tail & Finite Acceptance

  15. Axial Anomaly and the LTPuzzle N. Kochelev and Y. Oh; arXiv:1103.4891v1

  16. Systematic Uncertainties

  17. 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: • Almost final target polarizations (J. Singh) Waiting to receive final numbers very soon. • Elastic analysis as a cross check of systematics (V. Laine) • 2.1 GeV completed; working on other energies now • Acceptance: very messy but making steady progress • Finalize radiative corrections (J. Singh, T. Holmstrom& V. S.)

  18. 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

  19. Cross Section Smoothing 3.319 GeV, 9o Work by T. Holmstrom 4.404 GeV, 9o

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

  21. 6o Acceptance Solutions • ||  3.6% • Removed edge bins with a secondary process • Corrected remaining edge imperfections with • a secondary acceptance correction

  22. 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

  23. Variation of Acceptance Cuts Varying acceptance cuts does not help

  24. Elastic Asymmetry Analysis Work by V. Laine`

  25. 3He Elastic Acceptance Delta ytg W-M

  26. Elastic Cross Section Analysis Average 10 A; VDC 19% multi-tracks Work by V. Laine`

  27. Kinematic Coverage

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