[Phys-L] muon g minus 2

[John Denker <jsd@av8n.com>]

On 4/7/21 10:27 PM, bernard cleyet wrote:

> https://www.livescience.com/muon-wobble-could-break-physics.html
Yeah, that's amusing.

Upstream reference:
  https://news.fnal.gov/2021/04/first-results-from-fermilabs-muon-g-2-experiment-strengthen-evidence-of-new-physics/

This is a preliminary report; they have analyzed only 6% of the data the experiment is expected to produce. More data will shrink the experimental uncertainty.

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It is also amusing to note that the /theoretical/ number has some nontrivial uncertainty. That's because it is exceedingly hard to calculate. It's based on a power series, and you have to estimate the magnitude of the terms you're not including.

So there is some uncertainty, even if you do everything right.

And then if there are mistakes, the number could be wrong, outside the error bars. There's an amazing story about this. Tom Kinoshita is a reeeeally smart guy, and spent many years working on g-2 and similar calculations. Lots of brain cycles and lots of computer cycles. But at one point he published a wrong number, wrong in the 9th decimal place, which was way outside the error bars. That's because he got betrayed by the computer-algebra package he was using. It took years to sort this out.

Details here:
  https://physicstoday.scitation.org/doi/full/10.1063/1.1461321

Since the experimental uncertainty will soon be smaller than the theoretical uncertainty, we need somebody to revisit the calculation, to include more terms. Computers are orders of magnitude more powerful now, which might help a little, but even so, I reckon this is a super-hard job.

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I also wonder if muonium experiments (in contrast to storage-ring experiments) can contribute anything to this adventure.

No matter what happens, I reckon it's gonna be years before we know what this really means. It's sort of a lamppost with a sign that says "Look Here".