After a two-decade wait that included a long struggle for funding and a move halfway across a continent, a rebooted experiment on the muon — a particle similar to the electron but heavier and unstable — is about to unveil its results. Physicists have high hopes that its latest measurement of the muon’s magnetism, scheduled to be released on 7 April, will uphold earlier findings that could lead to the discovery of new particles.

The Muon g – 2 experiment, now based at the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, first ran between 1997 and 2001 at Brookhaven National Laboratory on Long Island, New York. The original results, announced in 2001 and then finalized in 2006¹, found that the muon’s magnetic moment — a measure of the magnetic field it generates — is slightly larger than theory predicted. This caused a sensation, and spurred controversy, among physicists. If those results are ultimately confirmed — in next week’s announcement, or by future experiments — they could reveal the existence of new elementary particles and upend fundamental physics. “Everybody’s antsy,” says Aida El-Khadra, a theoretical physicist at the University of Illinois at Urbana-Champaign.