Proton Compton Scattering from Linearly Polarized Gamma Rays.

Area of Science:

• Nuclear Physics
• Particle Physics
• Quantum Electrodynamics

Background:

• Understanding the proton's structure and electromagnetic properties is crucial in nuclear and particle physics.
• Proton polarizabilities offer insights into the distribution of charged matter within the proton.
• Previous measurements and theoretical frameworks provide a basis for new experimental investigations.

Purpose of the Study:

• To precisely measure differential cross sections for Compton scattering off the proton.
• To extract the electromagnetic dipole (α_{E1}^{p}) and magnetic dipole (β_{M1}^{p}) polarizabilities of the proton.
• To interpret the results within the chiral effective field theory framework for a deeper understanding of proton structure.

Main Methods:

• Differential cross sections were measured using quasimonoenergetic, linearly and circularly polarized photon beams.
• Experiments were conducted at the High Intensity Gamma-Ray Source facility at Triangle Universities Nuclear Laboratory.
• Scattering angles of 55°, 90°, and 125° were utilized with photon energies around 83 MeV.

Main Results:

• The electromagnetic dipole polarizability of the proton was determined to be α_{E1}^{p} = 13.8 ± 1.2_{stat} ± 0.1_{BSR} ± 0.3_{theo} × 10^{-4} fm³.
• The magnetic dipole polarizability of the proton was found to be β_{M1}^{p} = 0.2 ∓ 1.2_{stat} ± 0.1_{BSR} ∓ 0.3_{theo} × 10^{-4} fm³.
• Results were compared with previous measurements and theoretical predictions.

Conclusions:

• The study provides new, precise values for proton polarizabilities, contributing to the understanding of its internal structure.
• The extracted polarizabilities are consistent with predictions from chiral effective field theory.
• These findings refine our knowledge of low-energy quantum chromodynamics and electromagnetic interactions with the proton.