UIUC researchers held major role in Fermilab experiment; results could defy laws of physics

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Findings tell us about a "part of the universe that we have not yet observed.”

The Muon g-2 ring sits in its detector hall amidst electronics racks, the muon beamline, and other equipment. This impressive experiment operates at negative 450 degrees Fahrenheit and studies the precession (or wobble) of muons as they travel through the magnetic field. Photo by Reidar Hahn/Fermilab

URBANA-CHAMPAIGN, Ill. (WCIA) — The science world is abuzz Wednesday following new groundbreaking results of an experiment conducted at Batavia’s federally-run particle accelerator lab.

The Associated Press reported that initial results from two experiments are suggesting physicists could be incorrect in how they have thought the universe operates on a subatomic level.

Miniscule particles didn’t perform as expected when they were spun around two different long-running experiments in the U.S. and Europe. One of those tests was held at the U.S. Dept. of Energy’s Fermi National Accelerator Laboratory in Batavia.  

A press release from the U. of I. Grainger College of Engineering says these results confirm a discrepancy that has been “gnawing at researchers for decades.”

The release adds that U. of I. physicists in Champaign-Urbana played a major role in developing these new findings, as they confirm a result from an experiment performed 20 years ago. That happened at the Brookhaven National Lab, and it included those same physicists who have links to central Illinois.

“It was extremely exciting to produce such a tantalizing result,” says Paul Debevec, U. of I. emeritus physics professor. He was also involved in the Brookhaven experiment.

“We knew that we were going to have to do the experiment again — and do it better,” Debevec says. “What we didn’t know at the time was that it would take us 20 years to get to a new result”.

The startling particles in question are called ‘muons’. They are the close-relative of an electron — which orbits an atom — but they are about 200 times as massive.

Muons are also unstable and they normally exist for just 2 microseconds.

The press release says that muons occur naturally when cosmic rays hit Earth’s atmosphere — and the Fermi particle accelerator can produce them in large quantities.

“Like electrons, muons act as if they have a tiny internal magnet,” says the release. “In a strong magnetic field, the direction of this magnet precesses, or wobbles, much like a spinning top or gyroscope.”

That internal magnetic force determines the rate at which muons wobble while inside an external magnetic field. That rate is named by scientists as a ‘g-factor’.

Physicists say they can calculate that figure with extreme precision.

When muons are passed through the experiment, they also interact with a quantum foam of subatomic particles that pop in and out of existence, says the release. Those interactions have an effect on the value of the g-factor, by either speeding up or slowing down the rate it wobbles at.

Quantum foam is a term used to describe the fluctuation of space-time on small scalesee the below video for a short explanation.

Researchers say the Standard Model of Physics can accurately predict this anomalous magnetic moment. However, if the quantum foam holds extra forces or particles not accounted for in the Standard model, it would further affect the muon g-factor.

“Our measurement tells us how the muon interacts with everything else in the universe,” says Sudeshna Ganguly, a UIUC postdoctoral researcher on this project. Ganguly also recently took up a scientific position at the Fermi lab.

“When the theorists calculate the same quantity, using all of the known forces and particles in the Standard model, we don’t get the same answer,” says Ganguly. “That might mean that this result is telling us about a part of the universe that we have not yet observed.”

“The calculation of the muon’s behavior is just as important as the measurement. This is another place where UIUC scientists have played a key role,” continues the release.

U. of I. Physics Prof. Aida El Khadra says when the experiment was proposed, one big question was whether they could calculate the theoretical expectation with enough accuracy.

El Khadra is also a co-chair of the Muon g-2 Theory initiative. That’s an international effort to  coordinate scientists on producing the most precise calculations possible when researching muon.

“We’ve made tremendous progress in recent years, and believe we will continue to improve the precision of the theoretical calculation as the experimental precision improves,” says El Khadra. “This result is the first step of several years of exciting science.”

The Brookhaven experiment offered hints that the behavior of muons was not in line with the Standard Model. The release says this new measurement from the Muon g-2 experiment at Fermi strongly aligns with the values found at Brookhaven  — and it diverges from theory with the most precise measurements to date.

U. of I. physicists say the combined results from Fermi and Brookhaven have a significance of 4.2 sigma. They say that’s a little shy of the 5-sigma threshold that scientists need to claim a discovery; however, it’s still compelling evidence of new physics.

The release says that Fermi Lab is reusing the main component from the Brookhaven experiment: a 50-foot-diameter superconducting magnetic storage ring. In 2013, it was shipped 3,200 miles by land and sea from Long Island to Batavia.

After it arrived, the release says, scientists could use the Fermi Lab particle accelerator and generate a very intense beam of muons. Over the next 4 years, scientists built the experiment; tuned a very uniform magnetic field; developed new techniques, instrumentations, and simulations; and tested the whole system.

“The Muon g-2 experiment sends a beam of muons into the storage ring, where they circulate thousands of times at nearly the speed of light,” the release says. “Detectors lining the ring allow scientists to determine how fast the muons are precessing.”

Now, researchers say they’ve finished analyzing the movements of over 8 billion muons from the experiment’s first run in 2018.

“After the 20 years that have passed since the Brookhaven experiment ended, it is so gratifying to finally be resolving this mystery,” says Fermi Lab scientist Chris Polly, who also helped with the Brookhaven experiment as a U. of I. graduate student.

U. of I. Postdoctorate Adam Schreckenberger says they’ve analyzed under 6% of the data that the experiment will eventually collect.

“Although these first results are telling us that there is an intriguing difference with the Standard model, we will learn much more in the next couple of years,” Schreckenberger says.

“Pinning down the subtle behavior of muons is a remarkable achievement that will guide the search for physics beyond the Standard model for years to come,” says U. of I. Physics Professor and Fermilab Chief Research Officer Kevin Pitts.

“This is an exciting time for particle physics research, and Fermilab is at the forefront.”

Kevin Pitts

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