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Measurement of the proton spin structure function g1(x,Q2) for Q2 from 0.15 to 1.6 GeV2 with CLAS
R Fatemi1, A V Skabelin, V D Burkert
1University of Virginia, Charlottesville, VA 22901, USA.
Physical Review Letters
|December 20, 2003
Summary
Measurements of electron-proton scattering reveal the polarized structure function g1(x,Q2) and its first moment Gamma1(Q2). A significant change in Gamma1(Q2) was observed, particularly in the nucleon resonance region.
Area of Science:
- Nuclear Physics
- Particle Physics
- Quantum Chromodynamics
Background:
- Understanding the nucleon's internal structure is crucial in particle and nuclear physics.
- Polarized deep inelastic scattering experiments probe the spin-dependent structure functions of the nucleon.
Purpose of the Study:
- To measure double-polarization asymmetries in inclusive electron-proton scattering.
- To extract the polarized structure function g1(x,Q2) and its first moment Gamma1(Q2).
- To investigate the behavior of Gamma1(Q2) in the nucleon resonance and deep inelastic regimes.
Main Methods:
- Utilized longitudinally polarized electrons (2.6 and 4.3 GeV) and a longitudinally polarized ammonia (NH3) target.
- Data collected using the CLAS detector at Jefferson Lab.
- Extracted g1(x,Q2) over a range of Q2 (0.15-1.64 GeV2) and determined contributions to Gamma1(Q2) up to 1.2 GeV2.
Main Results:
- The polarized structure function g1(x,Q2) was extracted across the nucleon resonance region and into the deep inelastic regime.
- Contributions to the first moment Gamma1(Q2) were determined up to Q2=1.2 GeV2.
- A rapid change in Gamma1(Q2) was observed for Q2<1 GeV2, including a sign change near Q2=0.3 GeV2, indicating dominant resonance contributions.
Conclusions:
- The results indicate dominant contributions from the resonance region to Gamma1(Q2) at low Q2.
- At Q2=1.2 GeV2, the experimental data lie below the predictions from perturbative QCD evolved scaling values.
- This study provides valuable data for understanding nucleon spin structure and testing theoretical models.
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