This Particle Isn't Following the Rules of Physics. Maybe the Rules Are Wrong.
For nearly a century, the magnetic anomaly of the fundamental particle known as a muon has served as a means to test theories against experimental reality.
Recently, an international collaboration powered by the U.S.-based Fermilab has released its most accurate data on this anomalous magnetic dipole moment, known as g-2 ('gee minus two').
These new results align closely with recent theoretical predictions, and will serve as a benchmark moving forward.
The Standard Model of Particle Physics is a remarkable scientific achievement spanning nearly a century, and its predictive power has proven incredibly consistent. However, any scientific model worth its salt also needs to withstand experimental scrutiny, and one of the places those tests are employed is Fermilab.
Starting in 2017, an international collaboration of scientists have used data from Fermilab's 50-foot-diameter magnetic ring to measure the wobble of a fundamental particle known as a muon in what is referred to as the lab's 'muon g-2 experiment.' More than 200 times heavier than electrons, muons only survive for a few microseconds, but they have spins that makes them act like tiny magnets. This wobble, or precession, is due to an external magnetic field is called a g-factor, and a century ago, this factor was found to be 2 (hence the name 'muon g-2 experiment'). However, the introduction of quantum field theory complicates this number by bringing strong, weak, and Higgs fields interactions into the equation. This slight deviation from the '2' prediction is known as the muon's anomalous magnetic dipole moment.
To better understand this anomaly, Fermilab has consistently released results from its run of experiments that stretches from 2017 to 2023. On June 3, 2025, the muon g-2 experiment finally released its full results, with a precision of roughly 127 parts-per-billion—the most sensitive and accurate measurement of the muon's magnetic anomaly to date. The results of the study were submitted to the journal Physical Review D.
'The anomalous magnetic moment, or g–2, of the muon is important because it provides a sensitive test of the Standard Model of particle physics,' Regina Rameika, the U.S. Department of Energy's Associate Director for the Office of High Energy Physics, said in a press statement. 'This is an exciting result and it is great to see an experiment come to a definitive end with a precision measurement.'
Understanding this precise measurement of muon g-2 can help scientists discover new physics, as any deviation between experimental results and theoretical predictions using the Standard Model could point toward unknowns in our understanding of the subatomic world. While experimental physicists work to perfect ways of measuring the magnetic anomaly, theoretical physicists—especially those participating in the Muon Theory Initiative, which released its own update in late May—have largely sorted themselves into two 'camps' when calculating this theoretical prediction, according to Ethan Siegel at Big Think. One camp takes a data-driven approach to Hadronic vacuum polarization and the other uses a computational-based Lattice quantum chromodynamics (QCD) technique.
In 2021, it appeared that Fermilab's initial results were much closer to the Lattice QCD computational calculations, dampening (but not eliminating) the possibility of new physics orbiting the muon. Now, with this new calculation in hand, scientists can move forward with renewed confidence in an experimental result that's been a popular test of the Standard Model of Physics for a century.
'As it has been for decades, the magnetic moment of the muon continues to be a stringent benchmark of the Standard Model,' Simon Corrodi, assistant physicist at Argonne National Laboratory and analysis co-coordinator, said in a press statement. 'The new experimental result sheds new light on this fundamental theory and will set the benchmark for any new theoretical calculation to come.'
This isn't the end for measuring the muon magnetic anomaly—the Japan Proton Accelerator Research Complex aims to make its own g-2 measurements in the 2030s (though Fermilab says that its initial precision will be worse than their own latest results).
Today, this muon g-2 result is a testament of the incredible engineering and multidisciplinary scientific effort required to uncover just a little bit more about our ever-mysterious universe.
You Might Also Like
The Do's and Don'ts of Using Painter's Tape
The Best Portable BBQ Grills for Cooking Anywhere
Can a Smart Watch Prolong Your Life?
Hashtags
Try Our AI Features
Explore what Daily8 AI can do for you:
Comments
No comments yet...
Related Articles
New York Times
3 days ago
- New York Times
Mary K. Gaillard, Physicist Who Probed the Subatomic Universe, Dies at 86
Mary K. Gaillard was 16 and still known as Mary Ralph when a boy in her neighborhood asked her what she wanted to do with her life. She told him that she wanted to be a physicist. 'A singularly unfeminine profession,' he replied. Decades later, that remark would inspire the title of Dr. Gaillard's memoir, 'A Singularly Unfeminine Profession: One Woman's Journey in Physics' (2015), in which she recounted a career spanning a golden age of particle physics, when the outlines of how nature behaves at subatomic scales were just beginning to emerge. Dr. Gaillard contributed key insights to what is now known as the Standard Model — scientists' best theory about the properties and interactions of elementary particles — while overcoming discrimination as one of the few women in her field and inspiring other female physicists to do the same. Physics was 'her life,' her son Bruno said. 'She was consumed by it.' Known to many as Mary K, sans period, Dr. Gaillard, who died on May 23 at 86, was the first woman hired by the physics department at the University of California, Berkeley, and later became a senior scientist at Lawrence Berkeley National Laboratory. But much of her groundbreaking work occurred earlier, during a long stint as an unpaid visiting scientist at the European Organization for Nuclear Research, or CERN, a laboratory on the Franco-Swiss border. She was 'brilliant at doing calculations,' said John Ellis, a physicist at King's College London, who collaborated with Dr. Gaillard at CERN. 'If she calculated something, you could be sure that it was correct.' Want all of The Times? Subscribe.
New York Post
4 days ago
- New York Post
Radioactive wasp nest found at American Cold War-era nuclear bomb site
Workers at a site in South Carolina that once made key parts for nuclear bombs in the U.S. have found a radioactive wasp nest but officials said there is no danger to anyone. Employees who routinely check radiation levels at the Savannah River Site near Aiken found a wasp nest on July 3 on a post near tanks where liquid nuclear waste is stored, according to a report from the U.S. Department of Energy. 4 Employees who routinely check radiation levels at the Savannah River Site near Aiken found a wasp nest on July 3. AP Advertisement The nest had a radiation level 10 times what is allowed by federal regulations, officials said. The workers sprayed the nest with insect killer, removed it and disposed of it as radioactive waste. No wasps were found, officials said. The report said there is no leak from the waste tanks, and the nest was likely radioactive through what it called 'onsite legacy radioactive contamination' from the residual radioactivity left from when the site was fully operational. Advertisement 4 The workers sprayed the nest with insect killer, removed it and disposed of it as radioactive waste. andRiU – The watchdog group Savannah River Site Watch said the report was at best incomplete since it doesn't detail where the contamination came from, how the wasps might have encountered it and the possibility there could be another radioactive nest if there is a leak somewhere. Knowing the type of wasp nest could also be critical — some wasps make nest out of dirt and others use different material which could pinpoint where the contamination came from, Tom Clements, executive director of the group, wrote in a text message. 'I'm as mad as a hornet that SRS didn't explain where the radioactive waste came from or if there is some kind of leak from the waste tanks that the public should be aware of,' Clements said. Advertisement 4 The nest had a radiation level 10 times what is allowed by federal regulations, officials said. Getty Images/fStop The tank farm is well inside the boundaries of the site and wasps generally fly just a few hundred yards from their nests, so there is no danger they are outside the facility, according to a statement from Savannah River Mission Completion which now oversees the site. If there had been wasps found, they would have significantly lower levels of radiation than their nests, according to the statement which was given to the Aiken Standard. 4 If there had been wasps found, they would have significantly lower levels of radiation than their nests. ptoscano – Advertisement The site was opened in the early 1950s to manufacture the plutonium pits needed to make the core of nuclear bombs during the start of the Cold War with the Soviet Union. Now the site has shifted toward making fuel for nuclear plants and clean up. The site generated more than 165 million gallons (625 million liters) of liquid nuclear waste which has, through evaporation, been reduced to about 34 million gallons (129 million liters), according to Savannah River Mission Completion. There are still 43 of the underground tanks in use while eight have been closed.
San Francisco Chronicle
4 days ago
- San Francisco Chronicle
Radioactive wasp nest found at site where US once made nuclear bombs
COLUMBIA, S.C. (AP) — Workers at a site in South Carolina that once made key parts for nuclear bombs in the U.S. have found a radioactive wasp nest but officials said there is no danger to anyone. Employees who routinely check radiation levels at the Savannah River Site near Aiken found a wasp nest on July 3 on a post near tanks where liquid nuclear waste is stored, according to a report from the U.S. Department of Energy. The nest had a radiation level 10 times what is allowed by federal regulations, officials said. The workers sprayed the nest with insect killer, removed it and disposed of it as radioactive waste. No wasps were found, officials said. The report said there is no leak from the waste tanks, and the nest was likely radioactive through what it called 'onsite legacy radioactive contamination' from the residual radioactivity left from when the site was fully operational. The watchdog group Savannah River Site Watch said the report was at best incomplete since it doesn't detail where the contamination came from, how the wasps might have encountered it and the possibility there could be another radioactive nest if there is a leak somewhere. Knowing the type of wasp nest could also be critical — some wasps make nest out of dirt and others use different material which could pinpoint where the contamination came from, Tom Clements, executive director of the group, wrote in a text message. 'I'm as mad as a hornet that SRS didn't explain where the radioactive waste came from or if there is some kind of leak from the waste tanks that the public should be aware of,' Clements said. The tank farm is well inside the boundaries of the site and wasps generally fly just a few hundred yards from their nests, so there is no danger they are outside the facility, according to a statement from Savannah River Mission Completion which now oversees the site. If there had been wasps found, they would have significantly lower levels of radiation than their nests, according to the statement which was given to the Aiken Standard. The site was opened in the early 1950s to manufacture the plutonium pits needed to make the core of nuclear bombs during the start of the Cold War with the Soviet Union. Now the site has shifted toward making fuel for nuclear plants and clean up. The site generated more than 165 million gallons (625 million liters) of liquid nuclear waste which has, through evaporation, been reduced to about 34 million gallons (129 million liters), according to Savannah River Mission Completion.
