E97-110: Small Angle GDHExperimental Status Report

Vincent SulkoskyMassachusetts Institute of Technology

Hall A Collaboration MeetingDecember 9th, 2010

Introduction E97-110Precision 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

Neutron Spin Polarizabilities

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

Xee )',(He3

M. Amarian et al., PRL 89, 242301 (2002)

Analysis StatusPreliminary 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

asymmetryIssues 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

Elastic Asymmetry Analysis

Work by V. Laine`

Updated SAMC CodeWork done by V. Laine`SAMC rewritten in C++ from FortranImproved implementation of target

collimator cutsRaster correction by calculating electron’s

travel length through the cellRadiative 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

3He Elastic AcceptanceDelta

ytg W-M

tg tg

Acceptance Issues

Septum Mistuned

Delta Acceptance

E94-010

E97-110

• Flat region of -acceptance is much smaller with Septum• Simulation is not perfect on the falling edges

Solution

|| 3.6%Removed edge bins

with a secondary process

Corrected remaining edge imperfections with a secondary acceptance correction

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

Current WorkTarget 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 helpEstimation of QE contribution to

neutron results (V. Sulkosky)

SummaryWork is progressing though slowlyAcceptance analysis should be wrapping

up soonMajor work needs to go into radiative

corrections1. Finite acceptance for elastic tail subtraction2. Need a better technique to smooth the data3. Model for the two lowest energies

Draft of first paper in progress and expect to be internally available in January 2011

Systematic Uncertainties

Kinematic Coverage