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Nuclear Physics Seminars

ics Nuclear
Tuesday, November 11, 2003
3:30 PM
Physics Building, Room 204
Pibero Djawotho
College of William & Mary
"Measurement of the Neutron (3He) Spin Structure Functions at Low Q2; a Connection between the Bjorken and Gerasimov-Drell-Hearn Sum Rule"
ABSTRACT:
This talk presents results of experiment E94-010 performed at JLAB (simply known as JLab) in Hall A. The experiment aimed to measure the low Q2 evolution of the Gerasimov-Drell-Hearn(GDH) integral from Q2 = 0.1 to 0.9 GeV2. The GDH sum rule at the real photon point provides an important test of Quantum Chromodynamics (QCD) radiative rections. The low Q2 evolutions of the GDH integral contests various resonance models. Chiral Perturbation Theory and lattice QCD calculations, but more importantly, it helps us understand the transition between partonic and hadronic degrees of freedom. At high Q2, beyond 1 GeV2, the difference of the GDH integrals for the proton and the neutron is related to the Bjorken sum rule, another fundamental test of QCD radiative corrections. In addition, results of the measurements for the spin structure functions g1 and g2 cross sections, and asymmetries are presented. E94-010 was the first experiment of its kind at JLAB. It used a high-pressure, polarized 3He target with a gas pressure of 10 atm and average target polarization of 38%. For the first time, the polarized electron source delivered an average beam plarization of 70% with a beam current of 15 µa; The limit on the beam current was only imposed by the target. The experiment required six different beam energies from 0.86 to 5.1 GeV. This was the first time the accelerator ever reached 5.1 GeV. Both High-Resolution Spectrometers of Hall A, used in singles mode, were positioned at 15.5 degree; each.

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