Fermilab’s first Muon g-2 experiment results challenge known physics

Brittany A. Roston - Apr 7, 2021, 2:17pm CDT
Fermilab’s first Muon g-2 experiment results challenge known physics

Fermilab National Accelerator Laboratory has published its first results from the Muon g-2 experiment, hinting at ‘yet undiscovered particles or forces.’ At the core of the effort is confirmation that the particles referred to as muons do not behave as you’d expect based on the Standard Model of particle physics. This deviation, the lab notes, ‘might hint at exciting new physics.’

Muon particles are described as far more massive cousins to the electron. Fermilab notes that it is able to produce a large number of these particles using its particle accelerators — and, the lab explained as part of its announcement, it is able to calculate the muon’s g-factor number with incredible precision.

Using the Standard Model of particle physics, scientists are able to predict the g-factor, assuming there aren’t any other particles or forces that it fails to take into account. That’s where the milestone findings come in, with Muon g-2 experiment simulations manager Renee Fatemi explaining:

This quantity we measure reflects the interactions of the muon with everything else in the universe. But when the theorists calculate the same quantity, using all of the known forces and particles in the Standard Model, we don’t get the same answer. This is strong evidence that the muon is sensitive to something that is not in our best theory.

The results don’t quite meet the criteria for the scientists to announce a discovery, however, the odds that the results are caused by a statistical fluke is only around 1 in 40,000, according to Fermilab.

The findings are the result of four years of work that kicked off in 2018; more than 200 scientists from around the world participated in the experiment. At this time, Fermilab says, experts are analyzing data on the second and third experiment runs while the fourth run is underway.


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