Scientists working at Fermilab in Batavia, Illinois, have made some of the most important discoveries in physics over the years, including the existence of the top quark and the characteristic of the neutrino. According to the BBC, the team working on Fermilab’s Muon g-2 experiment reported a tantalizing hint of a new kind of physics. If confirmed, it will become the fifth fundamental force in the universe.
Our current understanding of particle physics is called the Standard Model, which we believe is an incomplete picture of the universe. Concepts such as the Higgs boson and dark energy do not fully integrate with the standard model, and the Muon g – 2 can ultimately help us understand why. The key to the breakthrough may be the behavior of the muon, a subatomic particle similar to an electron. The muon has a negative charge, but it is much more massive. It therefore rotates like a magnet, indicating a possible new branch of physics.
The roots of the Muon g – 2 experiment go back to the work done at CERN in the late 1950s. However, the instruments available at the time were too inaccurate to accurately measure the mu ‘g-factor’, describing the rate of flooding. The standard model predicts that muons wobble in a certain way, but the 14 meter magnetic accelerator in the heart of Muon g – 2 shows that muons have a different g-factor. This may not sound significant, but even a small ‘anomalous magnetic dipole moment’, as scientists call it, may indicate that something opaque affected the particles.
The 600-ton g-2 magnet before installation.
We currently know four fundamental forces: gravity, electromagnetism, the strong force (nuclear cohesion) and the weak force (radioactive decay). Whatever muons misbehaved in Muon g – 2 may be a fifth force, but we do not know what it is. Even if the team can confirm the outcome, we will not necessarily know what this new force of nature is doing, other than the disturbing muons. That section will require a lot more work. Theoretical physicists have speculated that the new force may be associated with an undiscovered subatomic particle such as the Z-prima boson or leptoquark.
The current focus is on improving the accuracy of the experiment. The new result was reported with a statistical confidence of 4.1 sigma, which works out to a 1 in 40,000 chance that the results are just statistical noise. Traditionally, scientists want to see a confidence of 5 sigma (about 1 in 3.5 million) before mentioning anything confirmed. This is something that physicists will be talking about a lot in the coming months.
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