Dr. Polly is part of an international team of 200 physicists from 35 institutions and seven countries who have been operating an experiment at Fermilab involving muons, subatomic particles that are akin to electrons but far heavier. When muons were shot through an intense magnetic field, they did not behave quite as expected, according to precise theoretical predictions.

“This quantity we measure reflects the interactions of the muon with everything else in the universe,” said Renee Fatemi, a physicist at the University of Kentucky. “This is strong evidence that the muon is sensitive to something that is not in our best theory.”

The results agreed with similar experiments at the Brookhaven National Laboratory in 2001 that have teased physicists ever since.

“After 20 years of people wondering about this mystery from Brookhaven, the headline of any news here is that we confirmed the Brookhaven experimental results,” Dr. Polly said at a news conference on Wednesday.