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The Forward Angle (Low Q 2 ) Neutron GDH Experiment

Experimental Overview. Preliminary Results. Polarized 3 He Target. Analysis Procedure:. 3 He as an effective n target:. The goal of Jefferson Lab experiment E97-110 is to study neutron and 3 He spin structure by performing a precise measurement of the generalized

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The Forward Angle (Low Q 2 ) Neutron GDH Experiment

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  1. ExperimentalOverview Preliminary Results Polarized 3He Target Analysis Procedure: 3He as an effective n target: 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. • Measure asymmetries andunpolarized cross sections. • Form polarized cross-section differences. • Extract structure functions and moments. 3He = Experimental Setup Effective polarized neutron target • Polarized electron beam, average Pbeam ~ 75% • Current ~ 1-10 mA • Hall A polarized 3He target (as effective neutron target) • Scattered electrons detected by a 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. 3He spin structure functions at constant Q2. Spin exchange optical pumping between Rb and 3He. • Target cells: 40 cm, ~ 10 atm • Highest polarized luminosity in the • world: up to 1036 cm-2 s-1 The GDH Experiments at JLab in Hall A GDH Sum Rule (Q2 = 0) Target Apparatus and Performance Sum Rule Static Properties measured theory well known • s1/2 and s3/2: cross sections for photoproduction • with two different photon polarizations. • Anomalous magnetic moment k: • measure of a particle’s deviation from • point-like behavior. • Can begeneralized for nonzero Q2. Neutron Integrals Generalized GDH (Q2 > 0) Polarized target setup. • Longitudinally and transversely polarized target. • Ptarg = 39% (preliminary analysis). • Target can now achieve in excess of 50% polarization! • Two independent polarimetries: NMR and EPR. • 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 do not agree well with Chiral • perturbation theory above 0.1 GeV2. • Present work, JLab experiment E97-110: • Benchmark check of chiral perturbation theory (cPT) calculations • in an unmeasured kinematic region where it should be valid. Polarized RB and 3He 220 oC 50 oC Polarized 3He only 3He standard target cell. Electron Beam First moment of the neutron g1 (left) and g2 (right) spin structure functions. The preliminary results (red triangles) show good agreement with both cPT calculations. The new data also show that the first moment of g2 is zero for our Q2 points indicating that the BC sum rule holds. Scattered Electrons DnaPHe* [3He] Special cell designed for forward angle detection. PHe = kw* SHe The Forward Angle (Low Q2) Neutron GDH Experiment Vincent Sulkosky (for the JLab Hall A Collaboration) Jefferson Lab, Newport News, VA 23606 → → 3He ≈ n Kinematic coverage. Target performance during experiment E97-110.

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