Date post: | 02-Jan-2016 |
Category: |
Documents |
Upload: | glenna-jacobs |
View: | 32 times |
Download: | 4 times |
Vincent SulkoskyMassachusetts Institute of Technology
Spokespeople: J.-P. Chen, A. Deur, F. Garibaldi
Hall A Collaboration MeetingDecember 10th, 2012
E97-110: Small Angle GDHExperimental Status Report
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
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)
Work in Progress
Finalize acceptance (V. Sulkosky)Radiative Corrections
◦ Preliminary work done by J. Singh◦ Work on going by Tim Holmstrom
Final NMR and EPR polarizations confirmed (J. Singh)Elastic 3He analysis (V. Laine)
◦ 2.1 GeV asymmetry and cross section completed◦ Now working on the other 3 data sets
Estimation of QE contribution to neutron results (V. Sulkosky)
9o Acceptance
Septum Mistuned5-10% uncertainty
Difficulty:◦ Saturation effect is present
◦ A few settings were mistuned with the septum magnet
◦ tg-acceptance appears squeezed at the highest field settings
◦ Only tight acceptance cuts improve the issues
Tools for Inelastic Cross Sections
Single Arm Monte-Carlo (SAMC) from A. Deur◦ Uses John LeRose transport functions at 9º and
apertures ◦ Updated septum magnet apertures with bore cooler◦ 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 removed using Rosetail averaged over the solid angle acceptance of E97-110
Acceptance Cut StudyCut na4: chosen as the reference cut to compare others against
Cross section angular differences corrected
using P. Bosted’s model
Summary of Cut StudyCut sc
[deg]tg
[mrad]
tg
[mrad]
Ytg
[cm]Pdiff [%]
[%]
Na1 9.002 8 3 4 -1.3 3.1
Na2 9.019 15 3 4 0.1 2.3
Na3 9.056 30 3 4 1.1 2.1
Na4 8.986 15 6 4 --- ---
Na5 8.920 15 12 4 -1.3 2.0
Na6 8.789 15 -18,8 4 2.0 4.1
Na7 8.67 15 -12,8 4 1.3 2.0
Na8 8.987 15 -6,12 4 -4.2 1.5
Na9 8.996 15 -6,15 4 -7.1 2.1
Na10 8.994 15 6 8 -2.1 1.5
Na11 9.249 20 6 8 -1.6 1.8Cross section cut sensitivity is typically less than 2%,
as long as tg is kept away from the small angle acceptance side
SummaryWork is progressingAcceptance analysis mostly completed;
currently checking other energies and yield stability
More work needs to go into radiative corrections:1. Smoothing of the data completed (T. Holmstrom)
2. Elastic tail subtraction with acceptance and collimator effects included
3. Model for the two lowest energiesDraft 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 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
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