In its most precise measurement to date, an international group of 200 scientists working at Fermilab has shown that a subatomic particle called the muon does not behave in a way predicted by the Standard Model of particle physics, which has long helped physicists understand and explain how the universe was created.

Particle physicist Kevin Pitts, who has worked on the Muon g-2 project for over a decade, is the former chief research officer at Fermilab, dean of Virginia Tech’s College of Science, and a professor in the Department of Physics. Pitts said the experiment is a breakthrough that could usher in an exciting new era of particle physics discoveries.

“This points to the potential of ‘new’ physics,” Pitts said. “New physics is a term that describes phenomena that we as human beings don’t yet understand. The experimental evidence is now quite solid and very much at odds with the theoretical predictions. We can’t rule out some problem or misunderstanding in the theory prediction, but another explanation is that some ‘new’ physics – a new force or particle for example – is causing the deviation. This is further indication that nature is not behaving quite as we expected. Exactly what that means is yet to be seen.”

A massive ring-shape particle accelerator inside the FermiLab's lower level.
To make their experimental measurement, scientists at Fermilab repeatedly sent a beam of muons into a 50-foot-diameter superconducting magnetic storage ring (above), where they circulated thousands of times at nearly the speed of light. Photo courtesy of Fermilab.

Pitts, the College of Science’s Lay Nam Chang Dean’s Chair, has worked extensively on a number of particle accelerator-based projects at Fermilab, including the ongoing Deep Underground Neutrino Experiment (DUNE) and the 1995 discovery of the “top quark.” Since joining Virginia Tech in 2022, Pitts has remained an active collaborator on the Muon g-2 experiment, working with graduate and postdoctoral researchers from the University of Illinois at Urbana-Champaign to determine how to best control and quantify the properties of the muon.

“Over the years, I have been very fortunate to work with fantastic undergraduate students, graduate students, and postdoctoral researchers,” Pitts said. “Their enthusiasm, intellect, and insight are truly remarkable. I am proud that former students have gone on to a variety of careers, ranging from medical physics to data science to particle accelerator technology.”

The muon, with about 200 times the mass of its cousin, the electron, occurs naturally when cosmic rays strike Earth’s atmosphere. Using a giant particle accelerator at Fermilab, scientists have produced muons in large numbers and observed a difference between how muons should behave according to the Standard Model and what they actually do inside the accelerator. The results indicate that muons could be interacting with yet-undiscovered subatomic particles or forces that exist in nature.

Two women, both with dark hair, stand in front of exterior stairs decorated with plants.
University of Illinois researchers Murong Cheng (left), Esra Barlas Yucel (right), and recent Ph.D. Cristina Schlesier (not pictured) are members of Pitts’ research team working on the Muon g-2 experiment. Photo courtesy of Kevin Pitts.

“The way a muon wobbles in a magnetic field tells us there’s something there we haven’t quantified in our theoretical understanding, and that’s quite exciting,” Pitts said. “The experiment has now spoken and that means there’s going to be a lot more attention paid to theory. It’s going to be fascinating over the next year or so to see the theoretical calculations refined and improved in that ongoing process.”

Patrick Huber, a Virginia Tech theoretical physicist who is director of the Center for Neutrino Physics and a member of the Particle Physics Project Prioritization Panel subcommittee that advises the Department of Energy’s Office of Science and the National Science Foundation, said: “It's great to see this new, improved experimental result at a time where we are also seeing huge progress in the theory calculation of g-2. I expect that very soon we will be able to confront these two ultra-precise results and thus look for new physics at unprecedented levels of sensitivity."

Share this story