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## Muon g-2 Result

7 Apr 2021, 17:45 UTC
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The long awaited FNAL muon g-2 result was announced today, you can watch a video of the seminar here, look at the paper and a discussion of it at Physical Review Letters, or read stories at Quanta and the New York Times. Tommaso Dorigo has an extensive discussion at his blog. In terms of the actual new result, it’s not very surprising: quite similar to the previous Brookhaven result (see here), with similar size uncertainties. It’s in some sense a confirmation of the Brookhaven result. If you combine the two you get a new, somewhat smaller uncertainty and ($a_\mu=\frac{1}{2}(g-2)$)
$$a_\mu(Exp)=116592061(41)×10^{−11}$$
The measurement uncertainties are largely statistical, and this is just using data from Run 1 of the experiment. They have accumulated a lot more data since Run 1, and once that is analyzed the FNAL experiment should be able to provide an experimental value with much lower uncertainty.
The big excitement over the g-2 experimental number has to do with it being in conflict (by 4.2 sigma now) with the Standard Model theoretical calculation, described here, which gives
$$a_\mu(Theory)=116591810(43)×10^{−11}$$
An actual discrepancy between the SM theory and experimental value would be quite exciting, indicating that something was missing from our ...