A new force of nature? Scientists close in on a fifth force as they discover a mysterious subatomic particle disobeying the laws of physics
- Physicists observed the ‘peculiar wobble’ of subatomic particle called a muon
- Modern understanding of physics may be missing an ‘unknown particle or force’
- The new findings replicate earlier results from 2021 but with four times the data
Scientists are closing in on potentially identifying a new force of nature after observing the peculiar ‘wobble’ of a subatomic particle.
The experts whizzed tiny muons, which are similar to electrons, through a 50-foot-diameter ring at the US Energy Department’s Fermilab in Batavia, Illinois.
Measurements of the muon’s magnetic ‘wobble’ can’t be explained by the Standard Model of particle physics – potentially hinting at some unknown particle or force.
Because muons form naturally when cosmic rays strike Earth’s atmosphere, these results could change how we believe the universe works.
The findings support earlier findings from 2021 but include more than quadruple the amount of data analysed, strengthening the claim for ‘new physics’.
The Muon g-2 ring sits in its detector hall at US Department of Energy’s Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois
What are muons?
Muons are negatively charged fundamental subatomic particles, similar to electrons but about 200 times as massive.
Importantly, muons are also magnetic, and wobble as they spin in the presence of a powerful magnetic field.
Their magnetic moment describes how strong their inherent magnets are, and how much a surrounding magnetic field causes the particles to wobble, or ‘precess’.
Scientists from Fermilab have detailed their work in a research paper submitted on Thursday to the journal Physical Review Letters.
‘We are looking for an indication that the muon is interacting with something that we do not know about,’ said study author Brendan Casey, senior scientist at Fermilab.
‘It could be anything – new particles, new forces, new dimensions, new features of space-time, anything.’
Casey theorisies that the results hint at a ‘new property of space-time’ or a violation of the Lorentz invariance, a principle stating that the laws of physics are the same everywhere.
‘That would be insane and revolutionary,’ he said.
For centuries, scientists have tried to work out what occurs at the ‘subatomic’ level, involving particles that are smaller than atoms.
Atoms, the basic units of matter that we can see and touch, combine to form molecules (which in turn form solids, gases, and liquids).
Physicists describe how the universe works at this fundamental subatomic level with a theory known as the Standard Model, developed in the early 1970s.
It suggests that everything in the universe is made from a few basic building blocks called fundamental particles, governed by four forces – the strong force, the weak force, the electromagnetic force, and the gravitational force.
The muons, which are similar to electrons, circulate thousands of times at nearly the speed of light in an attempt to measure how they ‘wobble’ over time
Called the Muon g-2 experiment, as the particles travelled along the 50-foot long magnetic track, they wobbled 0.1 per cent off the Standard Model that has been used for 50 years
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Researchers aimed to measure how magnetic muons are by watching them wobble as they travelled around the massive magnet
Over the 20th century, it became established as a well-tested physics theory and has precisely predicted a wide variety of phenomena.
However, the model cannot explain some of the deepest mysteries in modern physics, including what dark matter is made of and the imbalance of matter and antimatter in the universe.
To help solve some of these mysteries, researchers have been searching for particles behaving in different ways than would be expected in the Standard Model.
The recent experiments at Fermilab, referred to as Muon g-2, studied the wobble of muons as they traveled through a magnetic field.
The muon (pronounced mew-on) is a magnetic and negatively charged particle similar to its cousin the electron but 200 times more massive.
They form naturally when cosmic rays strike Earth’s atmosphere.
Importantly, muons are also magnetic, and wobble as they spin in the presence of a powerful magnetic field.
The muon, like the electron, has a tiny internal magnet that causes it to wobble – or, technically speaking, ‘precess’ – like the axis of a spinning top.
It measures ‘magnetic moment’ – the measure of the object’s tendency to align with a magnetic field
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The Fermilab experiment – conducted at unthinkably cold temperatures of -450°F (-268°C) – shot beams of muons into the donut-shaped superconducting magnetic storage ring measuring 50 feet (15 metres) in diameter.
The muons circulate thousands of times in the ring at nearly the speed of light in an attempt to measure how they ‘wobble’ over time.
As the muons zip around, they interact with other subatomic particles that, like tiny ‘dance partners’, alter their wobble.
Detectors lining the ring allowed scientists to determine how rapidly the muons were ‘precessing’.
Similar to results in 2021, the wobble’s speed, as measured in the experiment, varied considerably from what was predicted based on the Standard Model.
The muon’s ‘magnetic moment’ – the measure of the object’s tendency to align with a magnetic field – as a function of the particle’s spin is represented by the letter g, and according to theory should be a little larger than 2.
However, the newly announced measurements found the magnetic moment is stronger by about 0.2 parts per million, a small but significant amount.
The new effort replicates and improves upon a previous experiment at Brookhaven National Laboratory in New York, whose 2006 results were the first to suggest the muon’s behaviour differed from the Standard Model.
The subsequent measurements at Fermilab reinforced this result with more certainty, but none more so than the new results.
Results in 2021 similarly showed an anomalous wobble, but the new results were based on quadruple the amount of data, bolstering confidence in the findings.
The new effort replicates and improves upon a previous experiment at Brookhaven National Laboratory in New York, whose 2006 results were the first to suggest the muon’s behaviour differed from the Standard Model. The subsequent measurements at Fermilab reinforced this result with more certainty
The team is still working to integrate three more years of data together for a conclusive measurement of the muon’s so-called ‘magnetic moment’.
Ultimately, the findings continue to hint at some mysterious factor at play – potentially ‘unknown particles or forces’ that could rival the importance of the discovery of the Higgs Boson in 2012.
‘With all this new knowledge, the result still agrees with the previous results and this is hugely exciting,’ said study co-author Dr Rebecca Chislett at University College London.
Results further reinforce our team’s previous precise measurements of the muon’s anomalous magnetic moment, reaching unprecedented accuracy in testing the Standard Model and probing deeper into the subatomic world.’
EXPLAINED: THE STANDARD MODEL OF PHYSICS DESCRIBES THE FUNDAMENTAL STRUCTURE OF MATTER IN THE UNIVERSE
The theories and discoveries of thousands of physicists since the 1930s have resulted in a remarkable insight into the fundamental structure of matter.
Everything in the universe is found to be made from a few basic building blocks called fundamental particles, governed by four fundamental forces.
Our best understanding of how these particles and three of the forces are related to each other is encapsulated in the Standard Model of particle physics.
All matter around us is made of elementary particles, the building blocks of matter.
These particles occur in two basic types called quarks and leptons. Each consists of six particles, which are related in pairs, or ‘generations’.
All stable matter in the universe is made from particles that belong to the first generation. Any heavier particles quickly decay to the next most stable level.
There are also four fundamental forces at work in the universe: the strong force, the weak force, the electromagnetic force, and the gravitational force. They work over different ranges and have different strengths.
Gravity is the weakest but it has an infinite range.
The electromagnetic force also has infinite range but it is many times stronger than gravity.
The weak and strong forces are effective only over a very short range and dominate only at the level of subatomic particles.
The Standard Model includes the electromagnetic, strong and weak forces and all their carrier particles, and explains well how these forces act on all of the matter particles.
However, the most familiar force in our everyday lives, gravity, is not part of the Standard Model, and fitting gravity comfortably into this framework has proved to be a difficult challenge.
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