The Spin Structure of 3He and the Neutron at Low Q2:A Measurement of the Extended GDH Integral

Vincent Sulkosky (for the JLab Hall A Collaboration)Jefferson Lab, Newport News, VA 23606

Kinematic coverage.

Target performance during experiment E97-110.

Polarized 3He Target

Effective polarizedneutron target

3He as an effective n target:

3He n3He =

• Target cells: 40 cm, ~ 10 atm

• Highest polarized luminosity in the world: up to 1036 cm-2 s-1

Spin exchange optical pumping between Rb and 3He.

3He standard target cell.

Polarized RBand 3He

Polarized 3He only

220 oC

50 oC

Special cell designed forforward angle detection.

Electron Beam

Scattered Electrons

Target Apparatus and Performance

Polarized target setup.

• Longitudinally and transversely polarized target.

• Ptarg = 39% (preliminary analysis).

• Two independent polarimetries: NMR and EPR.

PHe = kw* SHe PHe* [3He]

Expected Results

• How do PT slopes compare to the new data?

• Is there a minimum and “turnover”?

E97-110 expected accuracy for the neutron generalized GDH integral. The red circles show the E94-010 results. The blue circles show the Q2 range, and the blue band shows the expected systematic uncertainty. The vertical axis has been normalized to the neutron value at the real photon point (233.2 b).

3He GDH integrand.

Analysis and Preliminary ResultsAnalysis Procedure:• Measure asymmetries and unpolarized cross sections.

• Form polarized cross-section differences.

• Extract structure functions and moments.

3He spin structure functions.

Experimental Overview

The goal of Jefferson Lab experiment E97-110 is to study neutron and 3Hespin structure by performing a precise measurement of the generalizedGerasimov-Drell-Hearn (GDH) integral at Q2 between 0.02 and 0.3 GeV2. The Experiment was run in summer 2003 in Hall A.

Experimental Setup

• Polarized electron beam, average Pbeam ~ 75%

• Current ~ 1-10 A

• Hall A polarized 3He target (as effective neutron target)

• Scattered electrons detected by Hall A High Resolution Spectrometer coupled with a septum magnet (inclusive reaction).

• Septum magnet: horizontal bending dipole magnet that enabled detection of electrons at 6 and 9 degrees.

The GDH Experiments at JLab in Hall AGDH Sum Rule (Q2 = 0)

• and: cross sections for photoproduction with two different photon polarizations.

• Anomalous magnetic moment : measure of a particle’s deviation from point-like behavior.

• Can be generalized for nonzero Q2.

Sum Rule Static Properties measured theory well known

Generalized GDH (Q2 > 0)

• Replace photoproduction cross sections with electroproduction (virtual photons).

• Previous JLab experiment E94-010:

Measured generalized GDH on neutron with Q2 between 0.1 to 0.9 GeV2.

Studied transition between strong interaction’s partonic to hadronic descriptions. Results did not agree well with Chiral perturbation theory above 0.1 GeV2.

• Present work, JLab experiment E97-110:

Benchmark check of chiral perturbation theory (PT) in a region where it should be valid.

Extrapolate to the real point (Q2 = 0).