By U.S. Department of Energy
October 19, 2022
In a new research study, researchers performed brand-new measurements of Compton spreading from the proton.
The proton is a nuclear particle with a favorable electrical charge found in the nucleus of an atom. It is a composite particle made up of essential building blocks of quarks and gluons. These parts and their interactions determine the protons structure, including its electrical charges and currents. When exposed to external electric and magnetic (EM) fields, this structure warps, a phenomenon called polarizability. The EM polarizabilities are a step of the stiffness against the contortion caused by EM fields.
By measuring the EM polarizabilities, scientists can find out about the internal structure of the proton. This knowledge assists to validate the scientific understanding of how nucleons (neutrons and protons) form by comparing the results to theoretical descriptions of gamma-ray scattering from nucleons. Physicists call this scattering procedure nucleon Compton scattering.
Compton scattering setup at the High Intensity Gamma Ray Source. The central cylinder is the liquid hydrogen target. High energy gamma rays are scattered from the liquid hydrogen into 8 big detectors that measure the gamma rays energy. Credit: Image thanks to Mohammad Ahmed, North Carolina Central University and Triangle Universities Nuclear Laboratory
The Impact
When researchers examine the proton at a distance and scale where EM responses dominate, they can identify values of EM polarizabilities with high precision. In this research, scientists confirmed EFTs using proton Compton scattering.
The proton is a nuclear particle with a positive electric charge located in the nucleus of an atom. These elements and their interactions identify the protons structure, including its electrical charges and currents. By measuring the EM polarizabilities, scientists can discover about the internal structure of the proton. When scientists take a look at the proton at a range and scale where EM actions dominate, they can determine values of EM polarizabilities with high precision. In this research, scientists confirmed EFTs using proton Compton scattering.
Summary
Proton Compton scattering is the procedure by which researchers scatter circularly or linearly polarized gamma rays from a hydrogen target (in this case, a liquid target), then measure the angular circulation of the scattered gamma rays. High-energy gamma rays carry strong enough EM fields that the reaction of the charges and currents in the nucleon becomes considerable.
In this research study, researchers performed brand-new measurements of Compton scattering from the proton at the High Intensity Gamma Ray Source (HIGS) at the Triangle Universities Nuclear Laboratory. This work offered a novel experimental method for Compton scattering from the proton at low energies using polarized gamma rays.
The study advances the requirement for new high-precision measurements at HIGS to improve the precision of proton and neutron polarizabilities decisions. These measurements verify the theories which link the low-energy description of nucleons to QCD.
Recommendation: “Proton Compton Scattering from Linearly Polarized Gamma Rays” by X. Li et al., 1 April 2022, Physical Review Letters.DOI: 10.1103/ PhysRevLett.128.132502.
This work was funded by the Department of Energy Office of Science, the National Science Foundation, the U.K. Science and Technology Facilities Council Grants, and funds from the Dean of the Columbian College of Arts and Sciences at George Washington University and its Vice-President for Research. The scientists likewise acknowledge the financial support of the Natural Sciences and Engineering Research Council of Canada and the support of Eugen-Merzbacher Fellowship.