TL;DR Science: A Muon Anomaly

By Erin Kang
May 12, 2021 · 3 minute read


Space Science

Recent evidence suggests that a tiny subatomic particle, referred to as the muon, could overturn the very foundation of physics and unlock the mysteries of the cosmos. Is this a bit dramatic? Perhaps. Is it warranted? Absolutely.

What is a muon?

The muon is a subatomic particle, which is similar to an electron but is about 207 times heavier, and is considered to be the building block of the universe. Muons and electrons both have the same electrical charge and similar quantum properties. However, because muons are much heavier than electrons, they have shorter lifetimes than electrons. Therefore, muons cannot play a crucial role in forming structures the way electrons can. So, what exactly is all the commotion about?

Muon g-2

Results from the Muon g-2 experiment at the US Department of Energy’s Fermi National Accelerator Laboratory showed that muon behavior deviated from the Standard Model (the current best theory describing the basic building blocks of the cosmos – quarks, leptons, bosons, and Higgs bosons – and their interactions). The deviation of the muons’ behavior within a magnetic field is slightly higher than the value predicted by the Standard Model.

Previously in 2001, experiments at the Brookhaven National Laboratory had presented similar results showing an aberration from the Standard Model. Unfortunately, the results were not statistically significant enough and that’s why the results weren’t valid. However, the more recent findings from the Muon g-2 experiment were statistically significant and confirmed the findings from 2001.


1933 – German physicist Paul Kunze observes the muon which he refers to as a “particle of uncertain nature”.

2001 – E821 experiment at Brookhaven National Laboratory. In the experiment, an accelerator called the Alternating Gradient Synchrotron created beams of muons and sent them into a 50-foot-wide storage ring controlled by magnets (Overbye). They found that the muons weren’t behaving as they were supposed to when a magnet field was present. These results were enough to pique researchers’ interest. The Alternating Gradient Synchrotron was retired due to lack of funds, and researchers were unable to redo the experiment.

2013 – At this time, Fermilab was interested in studying muons. At this new lab, Dr. Chris Polly, who had worked on the E821 experiment at Brookhaven persuaded the lab to continue what the Brookhaven Laboratory had started. In order to do so, Fermilab needed the Alternating Gradient Synchrotron. So, the Alternating Gradient Synchrotron took a little 3,200 – mile trip from Brookhaven to its new home in Fermilab. 

The picture below is the Alternating Gradient Synchrotron in all its 50 feet of glory journeying across the highway.

Image credit: Cindy Arnold/Fermilab, via US Department of Energy.

2020 – The Muon g-2 Theory Initiative, a group of 170 specialists, published a worldwide consensus of the muon magnetic moment calculation.

Present Day – People across the world watched the Zoom ceremony hosted by the g-2 team with bated breath as the experimenters revealed the results. The experiment involves a master clock that tracks the muons’ movement. In order to eliminate possible human bias, the master clock was set to an unknown rate. The number was the key to unlocking the data, and the results matched the results from Brookhaven.

Now what?

This anomaly has given inspiration to physicists to search for new particles and validate the new consensus value. Our current theory of the building blocks of the universe doesn’t have the answers to everything. The Standard Model can’t explain dark matter or what dark energy is. With the resulting anomaly in muon behavior, researchers will begin concocting new theories and explanations concerning the muon anomaly or the presence of new particles. Perhaps the Standard Model is simply an incomplete model or it could be a part of something far greater than we’ve ever imagined. According to Gordan Krnjaic, a cosmetologist at Fermilab, “The g-2 result could set the agenda for physics in the next generation.”

Video of the Muon experiment:


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About The Author

Erin Kang is a senior at James S. Rickards High School and is a part of the Sciteens team. Her hobbies include baking, listening to music, and playing the violin. If you have any questions or future article recommendations, feel free to contact her at


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