Compton-scattering cross section on the proton at high momentum transfer.

Area of Science:

• Nuclear Physics
• Particle Physics
• Quantum Chromodynamics

Background:

• Compton scattering provides insights into the proton's internal structure.
• Understanding photon-proton interactions is crucial for testing fundamental theories.

Purpose of the Study:

• To measure Compton scattering cross-sections on the proton.
• To investigate the scaling behavior of these cross-sections with energy.
• To compare experimental results with theoretical predictions, including perturbative QCD and the handbag mechanism.

Main Methods:

• Measurements were conducted at 25 kinematic settings.
• The kinematic range covered s=5-11 and -t=2-7 GeV^2.
• Statistical accuracy achieved was a few percent.

Main Results:

• The scaling power for the s dependence of the cross section at fixed center-of-mass angle was determined to be 8.0+/-0.2.
• This observed scaling power is strongly inconsistent with predictions from perturbative QCD.
• Experimental cross-section values showed fair agreement with calculations based on the handbag mechanism.

Conclusions:

• The study challenges the applicability of perturbative QCD in the measured kinematic regime.
• Results support the handbag mechanism as a viable model for Compton scattering on protons.
• The findings indicate that photons may interact with individual quarks within the proton.