The Wobbling Muons: A New Force in Physics?
Science & Technology - 10 Minute Read
An Overview
After scientists at Fermilab published data results in August claiming that strange subatomic particles by the name of muons were behaving in ways that modern physics could not explain, the jury has been out over whether or not there is an imminent renovation coming to the grand halls of physics.
Located in Batavia, Illinois, Fermilab has produced waves after waves of data supporting a claim that muons, heavier cousins of the electron, were wobbling a bit too much to modern-physics’s liking. The first of these data results came in 2006 but the accuracy of the findings fell largely short of the scientific standard required to be declared a discovery.
However, with the recent reproduction of the same data with commendable levels of accuracy by the physicists at Fermilab, even the most conservative and stubborn of scientists have begun to pay heed. The main reason for this being that the Standard Model of physics, established in the 1970s to unify three of the four forces that govern all matter, fails to explain why the muons at Fermilab are acting out.
The results of the muon experiments and, perhaps more importantly, their accuracy, are posing serious questions against the popular Standard Model of physics. Naturally then, to truly understand the significance behind these claims, one should first gauge an understanding of what the Standard Model is.
What is the Standard Model?
Known as one of the most crucial scientific propositions of the late 20th century, the Standard Model was proposed by a host of scientists, however most notably by the Nobel-prize-winning Steven Weinberg, as an attempt to unify three of the four known forces of the universe. These four forces were agreed to be the governing factors of all matter as we knew it. Therefore, any successful attempt at unifying them would be a major step forward in understanding the nature of the universe.
The three forces that the Standard Model successfully unified were the weak nuclear force, the strong nuclear force and the electromagnetic force. This unification was met with much commendation for the minds behind the discovery and was swiftly incorporated into many of the puzzling problems that physics was, and is, facing.
Despite this however, the Standard Model did have one gaping hole, the force of gravity. The Standard Model’s inability to incorporate gravitational forces, especially at the small quantum level, left many physicists sure that this Model had not yet achieved the status of being a Grand Unified Theory.
As time progressed and the Standard Model grew further and further embedded into modern physics, the continued omission of the gravitational force grew increasingly discomforting with the scientific community. These results from Fermilab, although do threaten to throw a spanner into the works of physics until an apt solution is found, offer a possible route out of science’s current dependence on the incomplete Standard Model.
Having now understood the stakes at hand, the findings of the muon experiments at Fermilab seem a great deal more significant to science as a whole. But how has a scientific theory as cemented into the pillars of physics as the Standard Model come under question because of a few wobbling particles?
The essence of the answer lies in the fact that the Standard Model should be able to explain the properties and behaviours, both orthodox and strange, of the muons in the Fermilab experiments. Curiously, it does not.
The late Steven Weinberg, an American theoretical physicist and Nobel-prize winner for his work on the unification of three of the four governing forces into the Standard Model.
Image Source: https://www.mercurynews.com/2021/07/24/nobel-prize-winning-physicist-steven-weinberg-dies-at-88/
The Nature of Muons
Muons have certain properties that are crucial in delivering the results that were attained at Fermilab last month. For instance, the particles are highly unstable, decaying into electrons within two-millionths of a second. This gave the scientists at Fermilab a way to quantify the number of muons before and after the experiments by measuring the presence of the excited electrons.
The other, and more critical, characteristic of muons is that they wobble when exposed to a magnetic field. The speed of this wobble is dependent on the magnetic moment of the muon particles, commonly referred to as the g-factor. According to the Standard Model, muons should have a g-factor of 2.
The scientists at Fermilab carried out an experiment where they accelerated the muon particles in a 14-metre long circular accelerator lined with sources of magnetic fields. Since muons were affected by the presence of these fields, they wobbled and spun as they went around the circular accelerator. With the g-factor of the muons assumed to be 2, the particles should have spun around their axis at exactly the same rate at which they went around the accelerator.
An analogy that explains this to some degree is the length of days and years for celestial bodies. To elaborate, the act of the muons wobbling in this analogy are like planets spinning about their axis and the act of the muons going around the circular accelerator can be represented by planets orbiting a star. The time it takes for a planet to complete a rotation around its axis is the length of a day, while the time it takes to complete a round orbit of a star is the length of a year. According to the Standard Model, the rate of spin and the rate of “orbit” of the muons should be the same; the length of a supposed “muon-day” should be the same as a “muon-year.”
(It should be noted that it is very tempting to use planetary orbits and its intuitive properties in our macrocosmic world as ways to explain particle physics but the world of the very small, at a quantum level, is very different from the supermassive scale of the planets. In this context though, the analogy gives us some simplification without seriously violating any quantum theories.)
A diagram depicting the Fermilab circular particle accelerator with the delivery rings for the different subatomic particles, including a delivery ring for Muons that was utilised in the recent experiments.
Image Source: https://www.fnal.gov/pub/science/particle-accelerators/accelerator-complex.html
The Fermilab Results
When the experiments at Fermilab were carried out however, the scientists calculated the g-factor to be just over 2, coming in at 2.002. The “muon-days” were shorter than “muon-years” when they should have been one and the same.
At first, there seemed to be a viable explanation for this fluctuation in the magnetic moment of the muons: the appearance of virtual particles. With quantum uncertainty, the “empty space” that the muons are accelerated around in cannot truly be empty. Instead, virtual particles blink in and out of existence with a strange, quantum transience. These virtual particles have been shown to affect the spin of muons by 0.1%(conveniently increasing the g-factor to 2.002), neatly proving why there was a slight fluctuation in the results.
This theory however, was proposed after the first findings of muonic fluctuations were recorded back in 2006. Since then, one of the goals of the repeated experiments in the last 6 years has been to reject this as an explanation and improve the accuracy of the experiments. This August, scientists at Fermilab have done just that.
The revised attempts at the muon experiments have taken the quantum appearances and effects of virtual particles into account but the results have still shown a clear discrepancy; virtual particles are not the answer. The implications of this are that there must be other forces or particles, unbeknownst to us, at play that are wobbling these muons.
On top of this, an element of the revised experiments at Fermilab that really drives home the argument for a proposed revision to the Standard Model is the accuracy of the experiments. When the experiment was first reenacted between 2018 and 2021 with the same findings as 2006, the results were accurate to 0.4 parts in a million. Another way of putting this is that there was a 1 in 2.5 million probability that the results were inaccurate.
This degree of accuracy unfortunately did not meet 5 sigma, a scientific standard for all results to be considered conclusive findings, denoting an accuracy around 0.3 parts in a million or a 1 in 3 million chance.
Amazingly, the results that came in last month had an astounding accuracy of 0.2 parts in a million or a 1 in 5 million chance of being inaccurate. This figure, along with the consistent findings from the experiments, formulates a strong argument against the Standard Model and its inability to explain these peculiar muons.
Fermilab’s results this year have doubled in accuracy when compared to their 2006 findings, clearing the 5-sigma requirement for all scientific discoveries.
Video Source: https://www.nytimes.com/2023/08/03/science/lk-99-superconductor-ambient.html
© Kabeer Hans, 2023
Conclusion
In summary, the results at Fermilab have proven, with double the prior accuracy, that muons are behaving in a way that the current state of particle physics cannot explain and has given scientists food for thought when it comes to the validity of the well-accepted Standard Model. Thorough papers that dive deeper into the results of these intriguing experiments are set to come out in 2025 but as of right now, the raw findings seem to have posed a substantial question by themselves. As Aida El-Khadra, a theoretical physicist at the University of Illinois, a two-and-a-half hour drive down from Fermilab, fittingly puts, “theory needs to get its act together.”
Bibliography
CERN. “Unified Forces | CERN.” Home.cern, 2023, home.cern/science/physics/unified-forces.
Cho, Adrian. “Does the Latest Measurement of the Muon Hint at New Physics?” Science, 10 Aug. 2023, www.science.org/content/article/does-latest-measurement-muon-hint-new-physics.
Choudhury, Rizwan. “New Force of Nature Discovered by Scientists at Fermilab.” Interestingengineering.com, 11 Aug. 2023, interestingengineering.com/innovation/new-force-of-nature-discovered-at-by-scientists-at-fermilab.
Crane, Leah . “Muons Are Still Behaving Oddly, Which Could Break Particle Physics.” New Scientist, 10 Aug. 2023, www.newscientist.com/article/2387085-muons-are-still-behaving-oddly-which-could-break-particle-physics/.
Fermilab. “Fermilab | Science | Particle Accelerators | Fermilab’s Accelerator Complex.” Www.fnal.gov, 2 Sept. 2023, www.fnal.gov/pub/science/particle-accelerators/accelerator-complex.html.
Miller, Katrina. “Physicists Move One Step Closer to a Theoretical Showdown.” The New York Times, 10 Aug. 2023, www.nytimes.com/2023/08/10/science/physics-muons-g2-fermilab.html. Accessed 8 Sept. 2023.
