Anomalous Magnetic Moment of Muon Even More Anomalous - Possible New Force of Nature

essentialsaltes

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Muons: 'Strong' evidence found for a new force of nature

There is currently a one in a 40,000 chance that the result could be a statistical fluke - equating to a statistical level of confidence described as 4.1 sigma.

A level of 5 sigma, or a one in 3.5 million chance of the observation being a coincidence, is needed to claim a discovery.

Prof Mark Lancaster, who is the UK lead for the experiment, told BBC News: "We have found the interaction of muons are not in agreement with the Standard Model [the current widely-accepted theory to explain how the building blocks of the Universe behave]."

The experiment, based at the Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, searches for signs of new phenomena in physics by studying the behaviour of sub-atomic particles called muons.

The Muon g-2 experiment involves sending the particles around a 14-metre ring and then applying a magnetic field. Under the current laws of physics, encoded in the Standard Model, this should make the muons wobble at a certain rate.

Instead, the scientists found that muons wobbled at a faster rate than expected. This might be caused by a force of nature that's completely new to science.

--

Per the "g-2" wiki link: A new experiment at Fermilab called "Muon g−2" using the E821 magnet will improve the accuracy of this value.[11] Data taking began in March 2018 and is expected to end in September 2022.[12] An interim result released on April 7, 2021[13] yields
9bc2859b6f0735e5d9ae6560eccbe2b9e04021d6
which, in combination with existing measurements, gives a more precise estimate
cf1f0af2d1721d8bbe9adb83103be161bd719d32
, exceeding the Standard Model prediction by 4.2 standard deviations.
 

FrumiousBandersnatch

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The plot thickens - a new supercomputer calculation by the BMW Group, based on the Standard Model, has produced a result closer to the empirical value than the International Group's prediction...

See 'What's Up With Muons?' from Sixty Symbols.

 
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Ponderous Curmudgeon

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The plot thickens - a new supercomputer calculation by the BMW Group, based on the Standard Model, has produced a result closer to the empirical value than the International Group's prediction...

See 'What's Up With Muons?' from Sixty Symbols.

And I just posted something on the demise of the Aether theory and here we have another one :)

Anyhow thank you for a very entertaining 30 minutes away from cleaning my living room.

Not to mention carrot sprout soup? LOL
 
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FrumiousBandersnatch

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sfs

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There is currently a one in a 40,000 chance that the result could be a statistical fluke - equating to a statistical level of confidence described as 4.1 sigma.
Okay, semi-pedantry here, but that's not right. A 4.1 sigma result means there is a 1 in 40,000 chance that if you made a measurement of g-2 and it really matched expectation, you'd get a result this far from the expected value. That's actually quite a different value than the probability that the observed result is nothing but a fluke. To calculate the latter, you have to know how likely genuine anomalies or, or equivalently, what the prior probability of a non-standard result is.
 
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Tinker Grey

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This video (at the this time code) addresses this "new force", why they are excited, why they are cautious, etc. It is both informative (and covers the 1/40000 stuff, too) and implicitly describes the scientific process. And too, why scientists enjoy the mystery, majesty of reality and why being found wrong is exciting. (The rest of the video is worth a watch, too.)

N.B. She's a PhD in Astrophysics.

 
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Ponderous Curmudgeon

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This video (at the this time code) addresses this "new force", why they are excited, why they are cautious, etc. It is both informative (and covers the 1/40000 stuff, too) and implicitly describes the scientific process. And too, why scientists enjoy the mystery, majesty of reality and why being found wrong is exciting. (The rest of the video is worth a watch, too.)

N.B. She's a PhD in Astrophysics.

(at the this time code)=11:30
 
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sjastro

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Over at one of the anti science hate sites the personnel over there are babbling on how physicists are imbeciles for worrying about the experimental vs theoretical value for the anomalous magnetic moment g-2 for the muon being accurate up to 'only' 7 decimal places.

To put this into perspective the QED (quantum electrodynamics) prediction versus experimental value for the g-2 measurement of the electron is compared.

g2.jpg

QED is the most accurate theory known in physics and the anomalous magnetic moment for the electron is accurate up to 11 decimal places.
It is therefore quite justifiable for physicists to view the discrepancy between the theoretical and experimental value for the anomalous magnetic moment of the muon as an indication of some unknown physics.

Such a consideration however needs to be treated with extreme caution.
Why You Should Doubt ‘New Physics’ From The Latest Muon g-2 Results
 
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sjastro

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The classical definition of a magnetic moment of a charged particle such as an electron or muon is that its spin and electric charge creates a magnetic dipole like a bar magnet.
In an external magnetic field a moment or torque is exerted on the magnetic dipole.

Using classical physics the orbital angular momentum around the nucleus and the intrinsic spin of the electron contribute to the magnetic dipole.

classical.png

The theoretical magnetic moment μ of an electron using classical physics is defined as:

μ = -(e/2mₑ)S

e, mₑ is the charge and mass of the electron respectively and S is spin of the electron.
The experimental value was out by a factor of about 2 to the theoretical value hence physicists introduced what amounted to a fudge factor g.

μ = -g(e/2mₑ)S

g ≈ 2 is known as the g factor.

Electrons cannot be defined as tiny orbiting and spinning balls using classical physics.
With the development of quantum mechanics and the work of Paul Dirac, spin in quantum mechanics is an intrinsic property of particles but cannot be physically interpreted in a classical sense.
For example fermions such as electrons and muons have a spin 1/2, bosons have a spin of 1 both of which are meaningless concepts in classical physics.
Dirac’s application of special relativity to quantum mechanics predicted g = 2 and the discrepancy between the theoretical and experimental values for the electron magnetic moment was considerably narrowed.

The difference between the quantum mechanical approach of Dirac and the experimental value for the electron became known as the anomalous magnetic moment ‘a’ where;

a = (g-2)/2

With the development of QED (quantum electrodynamics) which is a quantum field theory and states that a vacuum is a quantum field of the lowest energy level.
The anomalous magnetic moment could now be explained and predicted to an astonishing level of accuracy by the interaction of the electron field with the photon field of the vacuum.

The mathematical calculations for the predictions are complicated and can be explained by the use of Feynman diagrams.

QED.png

In the Dirac model the electron spin interacts only with the magnetic field and emits a photon γ.
In the QED model the ‘triangle’ part of the diagram which is a ‘loop’ in a Feynman diagram is the added interaction with the vacuum field and accounts for the anomalous electron magnetic moment.

The theory is similar for the anomalous muon magnetic moment but there is not the same level of accuracy which may suggest new physics.
 
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