Physicists On Verge Of Discovering New Subatomic Particle

Apr 13, 2021

Credit Reidar Hahn, Fermilab

Only 5% of the particles that make up the universe are currently known to physicists—but scientists believe a new particle is on the verge of being discovered.

Recent experiments conducted in Illinois show the potential for particles that are not predicted by the Standard Model, the system used to classify known particles and forces of nature. Los Alamos Scientist William Louis says Standard Model particles make up only a small part of the universe’s composition.

“The Standard Model particles make up only about 5% of the mass-energy of the universe. 95% of the mass-energy of the universe is unknown,” Louis said. “It's either in the form of dark matter, or dark energy. And so, the fact that there's all this missing energy, makes it not surprising that there could be a zoo of new particles.”

Fermilab’s Muon g-2 experiment tosses muons, a particle approximately 200 times heavier than an electron but similar in composition, into a magnetic field. Chris Polly, a senior scientist at Fermilab, described the experiment, detailing how his team studied muons traveling close to the speed of light. 

“You can think of muons as being little spinning tops, and if you put them in a magnetic field, they precess, they rotate,” Polly said. “They enter our storage ring, which you can basically think of as a racetrack for the muons. The muons go traveling around this racetrack at 99.94% the speed of light, revolving the whole time they're doing it. And our goal and experiment is to measure that revolution frequency extremely precisely.”

That measurement process recorded an anomaly, violating the predictions of the Standard Model. Scientist William Louis outlined the reason muon particles are optimal for such an experiment. He says the muon’s short lifespan of approximately two microseconds helps physicists conduct precise calculations.

“It's something that can be calculated extremely accurately,” Louis said. “And so, by measuring that, you can search for physics beyond the Standard Model, by seeing if you obtain, if you measure, a value different than expectation.”

Theoretical Physicist and New Mexico State University Professor Matthew Sievert says the discovery has the potential to help physicists understand more about dark matter.

“If this is true, if this continues to increase in statistical significance, then it would mean that we have discovered new particles,” Sievert said. “That we would have a window into what dark matter is...It would be a big step forward. It would give us clues about what a grand unified theory might be if we know what other particles and forces could be out there in nature.”

Fermilab will continue to conduct experiments in years to come to gather more data on the anomaly. William Louis, who works at Los Alamos National Laboratory, says that work in New Mexico will be influenced by the Fermilab experiments.

“It will spur, you know, additional experiments,” Louis said. “I work at Los Alamos National Laboratory, and it certainly already I think is affecting people at Los Alamos planning new experiments. And this will also be true at universities around New Mexico, at New Mexico State, at the University of New Mexico, and so forth. And, you know, physicists here in New Mexico can do experiments locally, but also they'll be involved in experiments at national labs around the world.”

NMSU’s Matthew Sievert stressed the work being done in the field of particle physics is a vital part of understanding just how the universe came to be.

“This gives us new insight into where we come from,” Sievert said. “This gives us new insight into what the fundamental fabric of the universe is and the history of how the universe came to be this way. We have to understand what matter is made of. We have to understand how matter interacts with each other to tell the story about how the universe came to be.”