E97-110: Small Angle GDHExperimental Status Report

Vincent SulkoskyMassachusetts Institute of Technology

Hall A Collaboration MeetingJune 9th, 2011

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:

Avg. Pbeam = 75%◦ Pol. 3He target (para & perp):

Avg. Ptarg = 40%

Measured polarized cross-section differences

Xee )',(He3

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

Kinematic Coverage

Current WorkWaiting on final target polarization (J. Singh)Elastic 3He analysis (V. Laine)

◦2.1 GeV asymmetry and cross section complete◦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)

Elastic Asymmetry Analysis

Work by V. Laine`

3He Elastic AcceptanceDelta

ytg W-M

tg tg

Elastic Cross Section Analysis

Work by V. Laine`

10 A; VDC 19% multi-tracks

Average

6o Acceptance Solutions

• || 3.6%• Removed edge bins with a secondary process• Corrected remaining edge imperfections with a secondary acceptance correction

9o Acceptance

Septum Mistuned15% uncertainty

More painful:◦ Saturation effect is present◦ A few settings were

mistuned with the septum magnet

◦ tg-acceptance appears squeezed at the highest field settings

Variation of Acceptance Cuts

Varying acceptance cuts does not help

Interpolation

• The interpolation method works, but there is a concern about the adjacent momentum settings.• Currently working on Carbon cross section analysis to verify the absolute normalization of the data.

• || 3.6%• Removed edge bins with a secondary process• Corrected remaining edge imperfections with a secondary acceptance correction

Cross Section Smoothing3.319 GeV, 9o

4.404 GeV, 9o

Work by T. Holmstrom

SummaryWork is progressing though slowlyHope to wrap up acceptance analysis

soonMajor work needs to go into radiative

corrections:1. Smoothing of the data completed (T.

Holmstrom)2. Finite acceptance for elastic tail subtraction3. Model for the two lowest energies

Draft of first paper in progress (75% complete) and expect to be internally available this month

Axial Anomaly and the LT Puzzle

N. Kochelev and Y. Oh; arXiv:1103.4891v1

Systematic Uncertainties

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:

◦ 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.)

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

Delta Acceptance

E94-010

E97-110

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

9-Degree AcceptanceMore painful:

◦Saturation effect is present

◦A few settings were mistuned with the septum magnet

◦tg-acceptance appears squeezed at the highest field settings