<< The long-awaited first results from the Muon g-2 experiment at the U.S. Department of Energy’s Fermi National Accelerator Laboratory show fundamental particles called muons behaving in a way that is not predicted by scientists’ best theory, the Standard Model of particle physics. >>️
<< Like electrons, muons act as if they have a tiny internal magnet. In a strong magnetic field, the direction of the muon’s magnet precesses, or wobbles, much like the axis of a spinning top or gyroscope. The strength of the internal magnet determines the rate that the muon precesses in an external magnetic field and is described by a number that physicists call the g-factor. This number can be calculated with ultra-high precision. >>
<< The first result from the Muon g-2 experiment at Fermilab confirms the result from the experiment performed at Brookhaven National Lab two decades ago. Together, the two results show strong evidence that muons diverge from the Standard Model prediction. >>
<< The accepted theoretical values for the muon are:
g-factor: 2.00233183620(86)
anomalous magnetic moment: 0.00116591810(43)
[uncertainty in parentheses]
The new experimental world-average results announced by the Muon g-2 collaboration today are:
g-factor: 2.00233184122(82)
anomalous magnetic moment: 0.00116592061(41)
The combined results from Fermilab and Brookhaven show a difference with theory at a significance of 4.2 sigma, a little shy of the 5 sigma (or standard deviations) that scientists require to claim a discovery but still compelling evidence of new physics. The chance that the results are a statistical fluctuation is about 1 in 40,000. >>️
We’re thrilled to announce that the first results from Fermilab’s Muon g-2 experiment strengthen evidence of new physics! #gminus2
https://t.co/tUx4ojzIps https://t.co/t1ufui2Mwu
17:01 Apr 7, 2021
Tracy Marc. First results from Fermilab’s Muon g-2 experiment strengthen evidence of new physics. Apr 7, 2021.
Also
Themis Bowcock, Mark Lancaster. How we found hints of new particles or forces of nature – and why it could change physics. Apr 8, 2021.
B. Abi et al. (Muon g−2 Collaboration)
Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm. Phys. Rev. Lett. 126, 141801. Apr 7, 2021.
A primer in particle physics:
Jonathan Carroll. Explainer: Standard Model of Particle Physics. Aug 25, 2011.
a 'cartouche' of the Standard Model
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