‘Wobbly’ muon hints at new force of nature

Researchers have gathered the firmest evidence yet that a tiny subatomic particle is disobeying the known laws of physics – a result that may hint at the existence of a new force of nature.

The findings from experiments in the particle accelerator at Fermilab, a large research facility near Chicago, disagree with previous studies.

Researchers have gathered the firmest evidence yet that a tiny subatomic particle is disobeying the known laws of physics – a result that may hint at the existence of a new force of nature.

The work involves a fundamental particle known as the muon and how it behaves when exposed to a powerful magnetic field. The latest experimental data suggests it “wobbles” more than the accepted laws of physics say it should. This raises the tantalising possibility it is interacting with a particle or force that would be new to science.

Results, if confirmed, would stand at odds with the standard model, the theoretical template used to explain the subatomic world for more than half a century, which takes in three of the fundamental forces that shape the universe: electromagnetism, the strong force that holds particles together and the weak force involved in radioactive decay.

However, it does not explain a fourth force – gravity – nor dark matter, which makes up most of the mass of the known cosmos. Knowing the model is incomplete, physicists have been attempting to move beyond it for decades. Hopes have been boosted that muons might provide the breakthrough.

Muons are fundamental particles similar to electrons but about 200 times as massive. Like electrons, they behave as if they have a tiny internal magnet that, in the presence of a magnetic field, precesses – or wobbles – like the axis of a spinning top. The precession speed in a given magnetic field depends on a property known as the muon magnetic moment. It is represented by the letter “g” and, at the simplest level, theory predicts g should equal two.

The difference of g from two – or g-two – can be attributed to a muon’s interactions with other particles that blink in and out of existence around it. These can be thought of as subatomic “dance partners” that alter the muon’s interaction with the magnetic field. The standard model incorporates all of the known dance partners and predicts how they would change the value of g.

The latest observations of real muons travelling at close to the speed of light inside a particle accelerator at Fermilab, a large research facility near Chicago, disagree with those predictions.

The findings have been published in Physical Review Letters.

The Times