Q2 evolution of the neutron spin structure moments using a 3He target

Area of Science:

• Nuclear Physics
• Particle Physics
• Quantum Chromodynamics

Background:

• Spin structure functions g(1) and g(2) probe the internal spin dynamics of nucleons.
• Helium-3 (3He) is a key nucleus for studying neutron spin properties due to its simple structure.
• Understanding these functions is crucial for testing theoretical models in quantum chromodynamics.

Purpose of the Study:

• To measure spin structure functions g(1) and g(2) of 3He.
• To determine the Q2 evolution of integral g(1)dx, integral g(2)dx, and d(2) for the neutron.
• To test the Burkhardt-Cottingham sum rule and the behavior of d(2).

Main Methods:

• A double-spin experiment involving inclusive scattering of polarized electrons off a polarized 3He target.
• Electron beam energies ranged from 0.862 to 5.058 GeV at a 15.5-degree scattering angle.
• Measurements covered excitation energies from the resonance to the onset of the deep inelastic regions.

Main Results:

• The Q2 evolution of Gamma(1)(Q2), Gamma(2)(Q2), and d(2)(Q2) for the neutron was determined for the first time in the range 0.1 <= Q2 <= 0.9 GeV2.
• Gamma(1)(Q2) showed a smooth variation across the measured Q2 range.
• The Burkhardt-Cottingham sum rule was found to hold within experimental uncertainties, and d(2) was observed to be nonzero.

Conclusions:

• The precise measurement provides valuable data for understanding neutron spin structure.
• The results support theoretical predictions regarding the behavior of spin structure functions at lower Q2.
• The nonzero value of d(2) offers further insights into nucleon spin physics.