E97-110: Small Angle GDH Experimental Status Report Vincent Sulkosky

E97-110: Small Angle GDH
Experimental Status Report
Vincent Sulkosky
Massachusetts Institute of Technology
Hall A Collaboration Meeting
June 9th, 2011
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

Neutron Spin Polarizabilities
Experiment E97-110

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3
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Inclusive experiment: He ( e , e' ) X
◦ Scattering angles of 6◦ and 9◦
◦ Polarized electron beam:
Avg. Pbeam = 75%
◦ Pol. 3He target (para & perp):
Avg. Ptarg = 40%

Measured polarized crosssection differences
M. Amarian et al., PRL 89, 242301 (2002)
Kinematic Coverage
Current Work
Waiting 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 Acceptance
Delta
tg
ytg
W-M
 tg
Elastic Cross Section Analysis
Average
10 A; VDC 19% multi-tracks
Work by V. Laine`
o
6 Acceptance
Solutions
• ||  3.6%
• Removed edge bins with a secondary process
• Corrected remaining edge imperfections with
a secondary acceptance correction
9o Acceptance

Septum Mistuned
15% 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
• ||  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.
• Currently working on Carbon cross section analysis to
verify the absolute normalization of the data.
Cross Section Smoothing
3.319 GeV, 9o
Work by T. Holmstrom
4.404 GeV, 9o
Summary
Work is progressing though slowly
 Hope to wrap up acceptance analysis soon
 Major work needs to go into radiative corrections:

1. Smoothing of the data completed (T. Holmstrom)
2. Finite acceptance for elastic tail subtraction
3. 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 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.)
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
Delta Acceptance
E94-010
• Flat region of
-acceptance
is much smaller
with Septum
• Simulation is not
perfect on the
falling edges
E97-110
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
`