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

E97-110 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)

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

3He Cross SectionsApplied very tight acceptance cuts on angles

with P. Bosted’s 2009 model

Acceptance Cut StudyAcceptance shows sensitivity to loose θtg cuts

Acceptance Cut StudyAcceptance shows sensitivity to loose φtg cuts, especially on

the negative side

Acceptance Cut StudyCut na4: chosen as the reference cut to compare others against

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

Back-up slides

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

Cross Section Smoothing

3.319 GeV, 9o

4.404 GeV, 9o

Work by T. Holmstrom

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

Radiative Tail & Finite Acceptance

Carbon Cross Section 2.007 GeV/c

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

Kinematic Coverage