The direct measurement of a proton's generalized polarizabilities in the strong quantum chromodynamics regime

Ingrid Fadelli is a writer for the website Phys.org.

The strong interactions between quarks are explored in quantum chromodynamic. Particles with an electric charge are called quarks.

Some aspects of the strong interactions in the quantum chromodynamics regime are still poorly understood. One theory that makes predictions about generalized polarizabilities is called chiral perturbation theory.

Chiral perturbation is an effective field theory. This theory is used to study low energy interactions in the quantum chromodynamics regime.

Researchers at the University of New Hampshire, University of Virginia, The College of William and Mary, and other institutions in the US and China have recently tested the predictions of a theory. The spin structure and generalized polarizabilities of a protons are measured in a paper published in Nature Physics.

According to Karl Slifer, one of the researchers who carried out the study, there are only a few characteristics of the protons. It's important that we understand the few properties of the protons since it's a fundamental particle in all visible matter. The theoretical understanding of one of these quantities, known as a generalized spin polarizability, was not very good a decade ago.

The main goal of the recent work by Slifer and his colleagues was to measure generalized a protons spin polarizability in a reliable way. They used a solid ammonia target with a strong magnetic field to do this.

As the beam goes through the field on its way to the target, it causes a large deflection. It took a lot of engineering to get the reaction cross section from the scattered electrons that came from the target.

The internal spin structure of individual protons was measured by Slifer and his colleagues. They were able to extract important parameters from their data, such as the spin polarizability, twist 3 matrix element, and polarizability d 2.

Two main groups of theorists are doing calculations for this amount. Both predictions in principle follow the same assumptions and symmetries as quantum chromodynamics. Direct tests of the theory of the strong force, known as QCD, are hard to come by.

The validity of theoretical predictions needs to be tested in an experiment. The findings gathered by Slifer and his colleagues can be used to improve our understanding of the strong quantum chromodynamics regime.

"These experiments are so difficult to run and to analyze that they are not available to the general public," Slifer said. Our results show that this kind of data can be used to clarify the spin- dependent properties of the protons. Our theory colleagues asked us to expand the measurement to higher energy. It will take a long time to run and analyze, but it should be finished.

There is more information about the spin structure and polarizabilities in the strong quantum chromodynamics regime.

Journal information: Nature Physics

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