E97-110: Small Angle GDH Experimental Status Report
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E97-110: Small Angle GDHExperimental Status Report
Vincent SulkoskyMassachusetts Institute of Technology
Hall A Collaboration MeetingDecember 15th, 2011
MotivationPrecision 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
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)
Current WorkWaiting 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)
9o Acceptance
Septum Mistuned15% uncertainty
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
Interpolation
• The interpolation method works, but there is a concern about the adjacent momentum settings.• 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
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
SummaryWork is progressingAcceptance analysis to be completed
soonMore 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 completed and internally circulated
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
6o Acceptance Solutions
• || 3.6%• Removed edge bins with a secondary process• Corrected remaining edge imperfections with a secondary acceptance correction
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
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