Muon anomaly: How a ‘last hope’ effort revolutionizes physics


Earlier this month, physicists at the Fermi National Accelerator Laboratory (Fermilab) near Chicago reported the results of the Muon g-2 experiment where they observed the oscillation of elementary particles called muons – and this oscillation has de profound implications for future studies.

The observation revealed that muons – elementary particles similar to electrons, only about 200 times more massive – oscillated more than originally expected as they hissed around a magnetized ring. However, a series of calculations published on the same day shed a different light on the results.

(Photo: Fermilab YouTube channel)

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Confirm an old anomaly

Nearly twenty years ago, physicists observed a supposed anomaly in the behavior of elementary particles, raising hopes of a revolutionary discovery. An experimental measurement attempt was carried out at Brookhaven National Laboratory in 2004, providing a value for the muon magnetic moment considered abnormal in the context of the Standard Model of particle physics.

Sixteen years later, an international team of more than 170 physicists co-published what has been labeled as “the most reliable prediction to date” for the theoretical value of the muon’s anomalous magnetic moment. However, the consensus value of adhering to the Standard Model varies considerably with Brookhaven’s 2004 observation.

Now, with the new Muon g-2 results at Fermilab, researchers now confirm that muon oscillation – their magnetic moment – aligns with the Brookhaven experiment of 2004 and differs from the theoretical consensus of 2020.

Basically, the latest findings on Muon g-2 suggest that there are still undiscovered particles that give muons that extra moment. Furthermore, further confirmation of this muon behavior could possibly break the Standard Model of particle physics, if not give rise to new physics. The Standard Model – which describes three of the known fundamental forces in the universe, with the exception of gravity – has been widely accepted as theoretically consistent for over fifty years.

Thinning the chances of a new physique

Adrian Cho, writing for the journal Science, also notes a concomitant report from the Budapest-Marseille-Wuppertal (BMW) collaboration contradicting the dominant theoretical prediction with another set of calculations. Using a modern technique called “quantum chromodynamics,” BMW physicists were able to calculate a value closer to experimental results and effectively create a strong bridge between experimental and theoretical estimates of the muon’s magnetic moment. Researchers from the BMW collaboration published their results in the journal Nature, in the article “Main Hadronic Contribution to the Muon Magnetic Moment of the QCD Grid.”

The perceived agreement between the latest experimental results of the Muon g-2 and the theoretical values ​​of BMW strongly suggests that the behavior of the muon is exactly what is predicted by the Standard Model, which gives credence to the particle physics model in force and lessens the chances of rebuttal or disruption. it down.

In a Quanta Magazine article, Aida El-Khadra, one of the co-organizers of Theory Initiative behind the 2020 Consensus and a Particle Theory with the University of Illinois, explains that the BMW calculation should also be taken at serious. She notes that this approach was not incorporated into the consensus because at the time it still needed “verification”. Once the BMW calculation – initially uploaded to the arXiv pre-print repository in February 2020 – has been independently verified by other research teams, it will be included by Theory Initiative in the next assessment of the “abnormal” muon oscillation.

Dominik Stöckinger, who is part of Theory Initiative and the Fermilab Muon g-2 team, said BMW’s calculations create “an unclear status”. He adds in the Quanta article that if the anomaly eventually disappeared, it would be “the end of particle physics” as some members of the particle physics community fear. Stöckinger called the muon g-2 experiment as their “last hope” to find physics beyond the Standard Model, and that if this failed, many researchers might feel the need to “give up” and “Do something else”, including himself.

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