Scaling tests of the cross section for deeply virtual Compton scattering

Area of Science:

• Nuclear Physics
• Particle Physics
• Quantum Chromodynamics

Background:

• Deeply Virtual Compton Scattering (DVCS) probes the internal structure of hadrons.
• Generalized Parton Distributions (GPDs) offer a 3D picture of quarks and gluons within protons.
• Experimental access to GPDs at moderate momentum transfer is crucial for understanding nucleon structure.

Purpose of the Study:

• To present the first measurements of the ep→epγ cross section in the DVCS regime.
• To investigate the Q² dependence of the helicity-dependent cross section.
• To provide model-independent measurements of GPDs and their integrals.

Main Methods:

• Measurement of the ep→epγ cross section using electron-proton scattering.
• Analysis of the Q² dependence of the helicity-dependent cross section.
• Extraction of helicity-independent cross sections.

Main Results:

• The Q² dependence of the helicity-dependent cross section confirms twist-2 dominance in DVCS.
• Generalized Parton Distributions (GPDs) are shown to be experimentally accessible at moderate Q² (1.5 to 2.3 GeV²).
• First model-independent measurements of GPD linear combinations and integrals up to twist-3 are presented.

Conclusions:

• The experimental results validate theoretical predictions regarding the dominance of twist-2 GPDs in DVCS.
• This work demonstrates the feasibility of probing GPDs experimentally.
• The presented measurements provide valuable data for constraining theoretical models of nucleon structure.