WASHINGTON, Aug 10 – The peculiar wobble of a subatomic particle called a muon in a U.S. laboratory experiment is making scientists increasingly suspect they are missing something in their understanding of physics – perhaps some unknown particle or force.
Researchers on Thursday announced new findings about the muon (pronounced MEW-on), a magnetic and negatively charged particle similar to its cousin the electron but 200 times more massive, in their experiment at the U.S. Energy Department’s Fermi National Accelerator Laboratory in Batavia, Illinois.
The experiment examined the wobble caused by muons traveling through a magnet field. The muon, like the electron, has a tiny internal magnet that causes it to wobble – or, technically speaking, “precess” – like the axis of a spinning top while in a magnetic field.
But, when measured, the speed of the wobble was much different from the Standard Model, which explains the interaction of the building blocks of the universe, and is governed by the four fundamental forces.
The new findings, building on data released in 2021, continue to hint at some mysterious factor at play as the researchers try to sort out the discrepancy between the theoretical prediction and the actual experimental results.
“We are looking for an indication that the muon is interacting with something that we do not know about. Brendan Casey is a Fermilab senior scientist and co-author of a paper published in Physical Review Letters on these findings.
“I am a crazy person so this would be something I love, like a Lorentz violation. Or some new feature of space time itself. Casey continued, “That would be crazy and revolutionary.”
Casey was referring to the principle of Lorentz invariance, which states that laws of physics apply everywhere.
“It is reasonable to assume that the results could point to unidentified particles or forces, said University College London co-author Rebecca Chislett. “Currently due to new results in the theory community, it is difficult to say exactly what the discrepancy between the two (predicted muon behavior and observed behavior) is, but theorists are working hard to resolve this.”
The experiment was conducted at minus-450 degrees Fahrenheit (minus-268 degrees Celsius). The researchers shot beams of muons into a donut-shaped superconducting magnetic storage ring measuring 50 feet (15 meters) in diameter. As the muons zipped around the ring traveling nearly the speed of light, they interacted with other subatomic particles that, like tiny dance partners, altered their wobble.
The 2021results also showed a wobble anomaly. The new results were based on quadruple the amount of data, bolstering confidence in the findings.
“With all this new knowledge, the result still agrees with the previous results and this is hugely exciting,” Chislett said.
The researchers hope to announce their final findings using all of their collected data in about two years.
“The experiment measures how fast muons spin in a magnetic field. It is a simple concept. But to get to the required precision takes years of building the experiment and taking data. Data was taken from 2018 and 2023.. The new result is based on our 2019 and 2020 data,” Casey said.
“We need to wait for the Standard Model to catch up with us before we can make the best use of our data,” Casey said. We are baffled by the fact that there are several different methods of predicting what should happen in our experiment, and none are very accurate. So there is something very fundamental here we must be missing, which is very intriguing.”
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