Revealing Color Forces with Transverse Polarized Electron Scattering

Area of Science:

• Nuclear Physics
• Particle Physics
• Quantum Chromodynamics

Background:

• Understanding the nucleon's internal structure is crucial in particle physics.
• Spin-dependent nucleon structure functions probe fundamental interactions.
• Twist-3 matrix elements offer insights into quark-gluon dynamics.

Purpose of the Study:

• To measure double spin asymmetries using a polarized proton target and electron beam.
• To extract the twist-3 matrix element d[over ˜]_{2}^{p}.
• To investigate the flavor dependence of the average color Lorentz force.

Main Methods:

• Utilized the Spin Asymmetries of the Nucleon Experiment with beam energies of 4.7 and 5.9 GeV.
• Employed a large-acceptance detector to identify scattered electrons.
• Analyzed asymmetries to extract d[over ˜]_{2}^{p} across a Q² range of 2.0 to 6.0 GeV².

Main Results:

• Measured two double spin asymmetries over a wide Bjorken x range (0.3
• Extracted d[over ˜]_{2}^{p}, finding it has the opposite sign compared to most quark models and lattice QCD.
• Observed an unexpected scale dependence in the extracted matrix element.

Conclusions:

• The experimental results for d[over ˜]_{2}^{p} deviate from theoretical predictions.
• Combining proton and neutron data suggests the average color Lorentz force is flavor independent.
• The findings highlight the need for refined theoretical models of nucleon structure.