Download 3 He - Jlab Hall-A

The Spin Structure of
3He
and the Neutron at Low
2
Q:
A Measurement of the Extended GDH Integral
Vincent Sulkosky (for the JLab Hall A Collaboration)
Jefferson Lab, Newport News, VA 23606
Experimental Overview
The goal of Jefferson Lab experiment E97-110 is to study neutron and 3He
spin structure by performing a precise measurement of the generalized
Gerasimov-Drell-Hearn (GDH) integral at Q2 between 0.02 and 0.3 GeV2.
The Experiment was run in summer 2003 in Hall A.
Polarized
3He
3He
Analysis and Preliminary Results
Target
Analysis Procedure:
as an effective n target:
3He
• Measure asymmetries and unpolarized cross sections.
3He
=
Experimental Setup
• Form polarized cross-section differences.
n
• Extract structure functions and moments.
Effective polarized
neutron target
• Polarized electron beam, average Pbeam ~ 75%
• Current ~ 1-10 mA
Polarized RB
and 3He
• 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 A
GDH Sum Rule (Q2 = 0)
220 oC
Polarized 3He only
3He

3He
spin structure functions.
50 oC
standard target cell.
Spin exchange optical pumping between Rb and 3He.
Electron Beam
• Target cells: 40 cm, ~ 10 atm
Scattered Electrons
• Highest polarized luminosity in the
world: up to 1036 cm-2 s-1
Special cell designed for
forward angle detection.
3He
GDH integrand.
Target Apparatus and Performance
Sum
measured
Rule Static Properties
theory
well known
• s1/2 and s3/2: cross sections for photoproduction
with two different photon polarizations.
Kinematic coverage.
• Anomalous magnetic moment k:
measure of a particle’s deviation from
point-like behavior.

• Can be generalized for nonzero Q2.
Generalized GDH
(Q2
> 0)
Expected Results
Polarized target setup.
• Longitudinally and transversely polarized target.
Target performance during experiment E97-110.
• Ptarg = 39% (preliminary analysis).
• Replace photoproduction cross sections with electroproduction
(virtual photons).
• Two independent polarimetries: NMR and EPR.
• 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.
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 mb).
• Present work, JLab experiment E97-110:
Benchmark check of chiral perturbation theory (cPT) in a
region where it should be valid.
Extrapolate to the real point (Q2 = 0).
• How do cPT slopes compare to the new data?
PHe = kw* SHe
Dn a PHe* [3He]
• Is there a minimum and “turnover”?