For experimental physicists, the latest measurement of the muon is the best of times. For theorists there’s still work to do.

Colliding 300 billion muons over four years at the Fermi National Accelerator Laboratory in the U.S., the Muon g-2 Collaboration —a group of over 200 researchers—has measured the magnetic strength of the muon to unprecedented precision: accurate to 127 parts per billion.

These final results on the muon’s magnetic moment—measured by its frequency of the moment’s wobbling in an external magnetic field—are the end of a chain of experimental efforts going back 30 years and have been published in the journal Physical Review Letters.