strong force force

strong force force

credit: Thomas Jefferson National Accelerator Facility

When this elusive particle was discovered in 2012, there was much talk about the Higgs boson. Although this was stated as giving normal matter mass, interactions with the Higgs field only produce about 1 percent of the normal mass. The other 99 percent comes from phenomena involving the Strong Force, the fundamental force that binds small particles called quarks into larger particles called protons and neutrons that comprise the nuclei of atoms of ordinary matter.

Now, researchers at the US Department of Energy’s Thomas Jefferson National Accelerator Facility have experimentally derived the strength of the strong mightA quantity that strongly supports theories explaining that most of the mass or normal matter in the universe originated.

This quantity, known as the coupling of the strong force, describes how strongly two bodies interact or “couple” under this force. The strong force varies with the distance between the particles affected by the coupling force. Prior to this research, theories disagreed about how strong force coupling should behave over large distances: some predicted it should increase with distance, some predicted it should decrease, and some predicted it should be constant.

With the Jefferson Lab data, the physicists were able to determine the strong force coupling at the greatest distance yet. Their results, which provide experimental support for theoretical predictions, were recently featured on the cover of the journal particles,

“We are delighted and excited to have our effort recognized,” said Jian-Ping Chen, senior staff scientist at Jefferson Lab and co-author of the paper.

Although this paper is the culmination of years of data collection and analysis, it was not entirely intentional at first.

spinoff spin experiment

At small distances between quarks, the strong force coupling is small, and physicists can solve for this with a standard iterative method. However, over large distances, the strong force coupling becomes so large that the iterative method no longer works.

“It’s both a curse and a blessing,” said Alexandre Deur, a staff scientist at the Jefferson Lab and a co-author of the paper. “While we have to use more complex techniques to calculate this quantity, its true value highlights very important emerging phenomena.”

This includes a system that accounts for 99 percent of the normal mass in the universe. (But we’ll get to that in a bit.)

Despite the challenge of not being able to use the iterative method, Deur, Chen and their co-authors extracted the strongest force coupling between impacted bodies at the greatest distance ever observed.

He extracted this value from a handful of Jefferson Lab experiments that were actually designed to study something completely different: proton and neutron spin.

These experiments were conducted at the laboratory’s Continuous Electron Beam Accelerator Facility, a DOE user facility. CEBAF is capable of providing polarized electron beams, which can be directed at special targets containing polarized protons and neutrons in the experimental hall. when one electron beam is polarized, meaning that most of the electrons are all moving in the same direction.

These experiments shot Jefferson Lab’s polarized electron beam at a polarized proton or neutron target. During several years of data analysis that followed, the researchers realized that they could combine the collected information about protons and neutrons to derive strong force coupling over large distances.

“Only Jefferson Lab’s high-performance polarized electron beam, in combination with developments in polarized targets and detection systems, allow us to obtain such data,” Chen said.

They found that as the distance between the affected bodies increases, the strong force coupling increases rapidly before flattening out and becoming stable.

“There are some theories that predicted this should be the case, but this is the first time experimentally that we’ve actually observed it,” Chen said. “It tells us in detail how the strong force really works at the scale of the quarks that make up protons and neutrons.”

Leveling up largely supports theories

These experiments were conducted about 10 years ago, when the Jefferson Lab’s electron beam was able to deliver electrons up to 6 GeV in energy (it is now capable of up to 12 GeV). Detection of the strong force at these large distances required a low-energy electron beam: a low-energy probe allows access to longer time scales and, therefore, larger distances between affected particles.

Similarly, a high-energy probe is necessary to zoom in for scenes of small time scales and small distances between particles. Labs with high-energy beams such as CERN, Fermi National Accelerator Laboratory, and SLAC National Accelerator Laboratory have already investigated strong force coupling at these small spacetime scales, when this value is relatively small.

The zoom-in view presented by the high-energy beam showed that the quarks have a small mass, only a few MeV. At least, that’s the mass of his textbook. But when quarks with lower energies are probed, their mass effectively increases to 300 MeV.

This is because quarks assemble a cloud of gluons, the particle that carries the strong force as they move over great distances. The mass-producing effect of this cloud accounts for most of the mass in the universe—without this extra mass, the textbook mass of quarks could only be about 1% of the mass of protons and neutrons. The other 99% comes from this acquired mass.

Similarly, one theory holds that gluons are massless at short distances but effectively gain mass during onward travel. The leveling of the strong force coupling over large distances supports this theory.

“If gluons remained massive over long distances, the strong force coupling would continue to grow uncontrollably,” Deur said. “Our measurements show that the strong force coupling stabilizes” distance The probe becomes larger, which is an indication that gluons have gained mass through the same mechanism that gives protons and neutrons 99% of their mass.”

This means that strong force coupling over large distances is important to understand this Mass generation system. These results also help to verify new ways of solving the equations of quantum chromodynamics (QCD), the accepted theory describing the strong force.

For example, the flattening of the strong force coupling over large distances provides evidence that physicists can apply a new, state-of-the-art technique called anti-de Sitter/conformal field theory (AdS/CFT) duality. Is. The AdS/CFT technique allows physicists to solve equations non-iteratively, which can help with strong force calculations over large distances where iterative methods fail.

Conformity in “conformal field theory” means that the technique is based on a principle that behaves the same at all spacetime scales. Because the strong force coupling level off over large distances, it no longer depends on the spacetime scale, which means strong force is compliant and AD/CFT may be applied. While theorists are already applying AdS/CFT to QCD, it supports the use of data technology.

“AdS/CFT has allowed us to solve problems of QCD or quantum gravity that were hitherto intractable or very broadly addressed using very rigorous models,” Deur said. “It has yielded many exciting insights fundamental physics,

So, while these results were generated by experimentalists, they seem to impress theorists the most.

“I believe that this is a true breakthrough for the advancement of results Quantum Chromodynamics and hadron physics,” said Stanley Brodsky, emeritus professor and QCD theorist at SLAC National Accelerator Laboratory. “I congratulate the Jefferson Lab physics community, in particular, Dr. Alexandre Deur for this major advance in physics.”

Years have passed since the experiments that accidentally led to these results. A new suite of experiments now uses Jefferson Lab’s high-energy 12 GeV beams to explore nuclear physics.

“With all these past experiments, I am very happy that we have trained many young students and they are now leaders of future experiments,” Chen said.

Only time will tell what theories support these new experiments.


Nuclear physicist in search of squeezed proton


more information:
Alexandre Deur et al, Experimental determination of the QCD effective charge αg1(Q), particles (2022). DOI: 10.3390/particle5020015

Citation: Strength of the Strongest Force (2022, August 3) Retrieved on August 3, 2022 from https://phys.org/news/2022-08-strength-strong.html

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