91±¬ÁĎ professor of physics and 91±¬ÁĎ research professor emeritus are part of an international team that won the 2026 . The $3 million award is shared among roughly 400 scientists, including 18 other researchers from the 91±¬ÁĎ team. It celebrates decades of work to better understand the muon — a subatomic particle with anomalous properties. This collaborative effort could ultimately lead to the discovery of entirely new particles.

“A remarkable aspect of these experiments is that it took the collective talents and experience of scientists and engineers from particle, nuclear, atomic, optical, accelerator and theoretical physics communities to work coherently toward one single goal,” Hertzog said. “Together, we measured a property of the muon that encapsulates almost everything we know about modern physics from relativity to quantum mechanics to the zoo of particles that govern the fundamental forces that shape our world.”

The were established in 2012 to recognize research achievements in life sciences, fundamental physics and mathematics.Ěý

Muons, short-lived subatomic particles, are created for experiments by particle accelerators. They exist for a fraction of a second before decaying into electrons and even tinier particles called neutrinos. During their short life, muons exhibit magnetic properties that deviate slightly from the – the leading theory that describes the particles and forces that make up the universe, along with anything that exists that has not yet been discovered.

The experiments recognized by the Breakthrough Prize represent 60-plus years of work to find out exactly how far the muon’s magnetism strays from Standard Model predictions. The first experiments began in 1959 at the, also called CERN.Ěý

Hertzog’s group at the University of Illinois was involved in a later experiment at the in the mid-1990s. He joined the faculty at 91±¬ÁĎ in 2010 and helped develop a new experiment at (Fermilab) that in 2025 with record-setting precision.Ěý

While Hertzog and others have now completed their experimental measurements, theorists  continue to refine the predictions of the Standard Model. In time, the gap between theory and experiment — where the muon currently hovers — may vanish or persist. If the muon’s properties never fit the Standard Model, physicists may need to explore entirely new theories.Ěý

“No matter where the final theory settles, the comparison with our experiment will have important consequences and give us deep insight into the heart of matter,” Hertzog said.

Many 91±¬ÁĎ physicists have been recognized by Breakthrough Prizes since the prizes’ inception, including a banner year in 2021 that also featured a win in the life sciences category by Nobel Prize laureate , a 91±¬ÁĎ professor of biochemistry.

“The Breakthrough Prize has previously recognized 91±¬ÁĎ physicists for work that deepened our understanding of gravity, dark energy and dark matter,” said , 91±¬ÁĎ divisional dean of natural sciences in the College of Arts and Sciences. “This latest recognition is a testament to the value of large-scale collaborative physics research and we are very proud of the accomplishments of all of the 91±¬ÁĎ faculty, postdocs and students who contributed to this effort.”

A full list of current 91±¬ÁĎ researchers recognized by the 2026 prize . Learn about other 91±¬ÁĎ wins at the Breakthrough Prize here.Ěý

For more information, contact Victor Balta at balta@uw.edu.

The first results from the at the U.S. Department of Energy’s have revealed that fundamental particles called muons behave in a way that is not predicted by scientists’ best theory to date, the of particle physics. This landmark result, , confirms a discrepancy that has been gnawing at researchers for decades.

The strong evidence that muons deviate from the Standard Model calculation might hint at exciting new physics. The muons in this experiment act as a window into the subatomic world and could be interacting with yet-undiscovered particles or forces.

“This experiment is a bit like a detective story,” said team member , a 91±¬ÁĎ professor of physics and a founding spokesperson of the experiment. “We have analyzed data from the Muon g-2’s inaugural run at Fermilab, and discovered that the Standard Model alone cannot explain what we’ve found. Something else, perhaps beyond the Standard Model, may be required.”

The Muon g-2 experiment is an international collaboration between Fermilab in Illinois and more than 200 scientists from 35 institutions in seven countries. 91±¬ÁĎ scientists have been an integral part of the team through the  — constructing sensitive instruments and sensors for the experiment, and leading data analysis endeavors. In addition to Hertzog, current 91±¬ÁĎ faculty and lead scientists involved include , research professor of physics; Erik Swanson, a research engineer with the 91±¬ÁĎ’s , or CENPA; Jarek Kaspar, a research scientist; and , a professor of physics.

“The 91±¬ÁĎ custom-built instrumentation would not have been possible without the extraordinary dedication and expertise of our CENPA technical staff, who work closely with our postdocs and graduate students,” said Hertzog.

A muon is about 200 times as massive as its cousin, the electron. They occur naturally when cosmic rays strike Earth’s atmosphere. Particle accelerators at Fermilab can produce them in large numbers. Like electrons, muons act as if they have a tiny internal magnet. In a strong magnetic field, the direction of the muon’s magnet precesses, or “wobbles,” much like the axis of a spinning top. The strength of the internal magnet determines the rate that the muon precesses in an external magnetic field and is described by a number known as the g-factor. This number can be calculated with ultra-high precision.

As the muons circulate in the Muon g-2 magnet, they also interact with a “quantum foam” of subatomic particles popping in and out of existence. Interactions with these short-lived particles affect the value of the g-factor, causing the muons’ precession to speed up or slow down slightly. The Standard Model predicts with high precision what the value of this so-called “anomalous magnetic moment” should be. But if the quantum foam contains additional forces or particles not accounted for by the Standard Model, that would tweak the muon g-factor further.

Hertzog, then at the University of Illinois, was one of the lead scientists on the predecessor experiment at Brookhaven National Laboratory. That endeavor concluded in 2001 and offered hints that the muon’s behavior disagreed with the Standard Model. The new measurement from the Muon g-2 experiment at Fermilab strongly agrees with the value found at Brookhaven and diverges from theory with the most precise measurement to date.

The accepted theoretical values for the muon are:

• g-factor: 2.00233183620(86)
• anomalous magnetic moment: 0.00116591810(43)

The new experimental world-average results announced by the Muon g-2 collaboration today are:

• g-factor: 2.00233184122(82)
• anomalous magnetic moment: 0.00116592061(41)

The combined results from Fermilab and Brookhaven show a difference with theoretical predictions at a significance of 4.2 sigma, a little shy of the 5 sigma — or 5 standard deviations — that scientists prefer as a claim of discovery. But it is still compelling evidence of new physics. The chance that the results are a statistical fluctuation is about 1 in 40,000.

“This result from the first run of the Fermilab Muon g-2 experiment is arguably the most highly anticipated result in particle physics over the last years,” said Martin Hoferichter, an assistant professor at the University of Bern and member of the theory collaboration that predicted the Standard Model value. “After almost a decade, it is great to see this huge effort finally coming to fruition.”

The Fermilab experiment, which is ongoing, reuses the main component from the Brookhaven experiment, a 50-foot-diameter superconducting magnetic storage ring. In 2013, it was transported 3,200 miles by land and sea from Long Island to the Chicago suburbs, where scientists could take advantage of Fermilab’s particle accelerator and produce the most intense beam of muons in the United States. Over the next four years, researchers assembled the experiment; tuned and calibrated an incredibly ; developed new techniques, instrumentation, and simulations; and thoroughly tested the entire 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. Detectors lining the ring allow scientists to determine how fast the muons are “wobbling.”

Many of the sensors and detectors at Fermilab were constructed at the 91±¬ÁĎ, such as instruments to measure the muon beam as it enters the storage ring and to the telltale particles that arise when muons decay. Dozens of scientists — including faculty, postdoctoral researchers, technicians, graduate students and undergraduate students — have worked to assemble these sensitive instruments at the 91±¬ÁĎ and then install and monitor them at Fermilab.

91±¬ÁĎ scientists have also been involved in theoretical work around the Muon g-2 collaboration.

“The prospects of the new result triggered a coordinated theory effort to provide our experimental colleagues with a robust, consensus Standard-Model prediction,” said Hoferichter, who was a 91±¬ÁĎ research assistant professor from 2015 to 2019. “Future runs will motivate further improvements, to allow for a conclusive statement if physics beyond the Standard Model is lurking in the anomalous magnetic moment of the muon.”

In its first year of operation, in 2018, the Fermilab experiment collected more data than all prior muon g-factor experiments combined. The Muon g-2 collaboration has now finished analyzing the motion of more than 8 billion muons from that first run. The 91±¬ÁĎ team was central to this effort, leading to four doctoral theses to date.

Data analysis on the second and third runs of the experiment is under way; the fourth run is ongoing, and a fifth run is planned. Combining the results from all five runs will give scientists an even more precise measurement of the muon’s “wobble,” revealing with greater certainty whether new physics is hiding within the quantum foam.

“So far we have analyzed less than 6% of the data that the experiment will eventually collect,” said Fermilab scientist Chris Polly, who is a co-spokesperson for the current experiment and was a lead University of Illinois graduate student under Hertzog during the Brookhaven experiment. “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.”

“With these exciting results our team, in particular our students, is enthusiastic to push hard on the remaining data analysis and future data-taking in order to realize our ultimate precision goal,” said Kammel.

Hertzog will present the results at a 91±¬ÁĎ Department of Physics on April 12.

Adapted from a by Fermilab.