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posted by martyb on Thursday April 08 2021, @05:19AM   Printer-friendly
from the mysterious-muon-magnetic-moment dept.

Ars Technica

The Muon g-2 experiment (pronounced "gee minus two") is designed to look for tantalizing hints of physics beyond the Standard Model of particle physics. It does this by measuring the magnetic field (aka the magnetic moment) generated by a subatomic particle known as the muon. Back in 2001, an earlier run of the experiment at Brookhaven National Laboratory found a slight discrepancy, hinting at possible new physics, but that controversial result fell short of the critical threshold required to claim discovery.

Now, Fermilab physicists have completed their initial analysis of data from the updated Muon g-2 experiment, showing "excellent agreement" with the discrepancy Brookhaven recorded. The results were announced today in a new paper published in the journal Physical Review Letters.

Journal References:
1.) B. Abi, et al. Measurement of the Positive Muon Anomalous Magnetic Moment to 0.46 ppm [open], Physical Review Letters (DOI: 10.1103/PhysRevLett.126.141801)
2.) T. Albahri et al. (The Muon g−2 Collaboration) Magnetic-field measurement and analysis for the Muon g−2 Experiment at Fermilab [open], Physical Review A (DOI: 10.1103/PhysRevA.103.042208)
3.) T. Albahri et al. (Muon g−2 Collaboration)Measurement of the anomalous precession frequency of the muon in the Fermilab Muon g−2 Experiment [open], Physical Review D (DOI: 10.1103/PhysRevD.103.072002)


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  • (Score: 2, Interesting) by Anonymous Coward on Thursday April 08 2021, @05:35AM (5 children)

    by Anonymous Coward on Thursday April 08 2021, @05:35AM (#1134670)

    Peter Woit (writer of Not Even Wrong) points out that the theoretical calculation that is in contradiction with the experiment may be itself wrong: https://www.math.columbia.edu/~woit/wordpress/?p=12292 [columbia.edu]
    A new calculation of the same number is actually in agreement with the experiment.

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  • (Score: 3, Informative) by kvutza on Thursday April 08 2021, @11:30AM (1 child)

    by kvutza (11959) on Thursday April 08 2021, @11:30AM (#1134731)

    Welp, it is about not having a clearly correct theoretical prediction at this level preciseness: two ways to calculate one contribution differ and no one knows who is right. Notice that it is not about newer vs. older calculations, it is about two different methods.

    BTW Another blog post that discusses it.
    https://resonaances.blogspot.com/2021/04/why-is-it-when-something-happens-it-is.html [blogspot.com]

    • (Score: 0) by Anonymous Coward on Thursday April 08 2021, @09:15PM

      by Anonymous Coward on Thursday April 08 2021, @09:15PM (#1135010)

      Have tgey tried the new Common Core way to solve the equation, instead of the "old method?"

  • (Score: 0) by Anonymous Coward on Thursday April 08 2021, @01:19PM (1 child)

    by Anonymous Coward on Thursday April 08 2021, @01:19PM (#1134756)

    I hear that they had to throw out the standard model because it didn't predict global warming with sufficient speed, risking their funding.

    • (Score: 0) by Anonymous Coward on Thursday April 08 2021, @02:03PM

      by Anonymous Coward on Thursday April 08 2021, @02:03PM (#1134773)

      Ha, ha! The one thing that could finally bring down the Standard Model.

  • (Score: 2) by FatPhil on Friday April 09 2021, @11:00AM

    by FatPhil (863) <pc-soylentNO@SPAMasdf.fi> on Friday April 09 2021, @11:00AM (#1135261) Homepage
    > A new calculation of the same number is actually in agreement with the experiment.

    $$a_\mu(BMW)=116591954(55)×10^{−11}$$
    $$a_\mu(Exp)=116592061(41)×10^{−11}$$

    OK, it's not in actual disagreement, but the error bars don't touch, so "actually in agreement" is a bit of a stretch. In fact, the bell-curves line up at such a tantalising position that a claim of them being in agreement is on an equally weak footing as a claim of them being in disagreement. So best to not make either assertion just yet.

    Fortunately for the scientists, it definitely points to "we need to do more hard science to get closer to the truth".
    --
    Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves