Fundamentals of physics in question after new particle experiment

8 Apr 2022

The Collider Detector at Fermilab. Image: Reidar Hahn/Fermilab

The standard model of physics is under scrutiny after scientists found the mass of the W boson particle differed from predictions.

A new measurement of the mass of a sub-atomic particle, the W boson, has baffled physicists all over the world.

In what has been described as the “most precise measurement” to date, the particle was found to be heavier than predicted in the standard model of particle of particle physics, which has explained how the universe works for almost half a century.

Developed in the early 1970s, the standard model theory explains how the basic building blocks of matter interact, governed by four fundamental forces: gravitational, electromagnetic, strong and weak.

Since its inception, the standard model has successfully explained almost all experimental results and precisely predicted a wide variety of phenomena. Its veracity was cemented in 2012 when scientists used the Large Hadron Collider in Europe to discover the long-predicted Higgs boson, also known as the ‘God particle’.

The model is far from perfect, however. Most notably, it leaves out one of the four forces, gravity, and does not account for dark matter which likely constitutes most of the universe.

But now, a study measuring the mass of the W boson published in the journal Science yesterday (7 April) has scientists questioning the foundations of the standard model – and the discrepancy could hint to more particles or interactions waiting to be discovered.

‘There is something new in nature’

A team of around 400 scientists looking at old data collected from the Fermi National Accelerator Laboratory, or Fermilab, found the weight of the W boson – a messenger particle of the weak force – to be significantly heavier than predicted.

Based on a decade of work and with data fed from the Tevatron collider near Chicago that was active until 2011, the findings also disagree with previous W boson mass measurements.

“All these measurements claim to measure the same quantity,” Prof Martin Grünewald, an experimental physicist at University College Dublin, told Science. “Somebody must be, I will not say wrong, but maybe made a mistake or pushed the error evaluation too aggressively.”

But Prof Ashutosh Kotwal, who led this new analysis, is certain the updated measurement is accurate. “The number of improvements and extra checking that went into our result is enormous,” he said.

“We took into account our improved understanding of our particle detector as well as advances in the theoretical and experimental understanding of the W boson’s interactions with other particles. When we finally unveiled the result, we found that it differed from the standard model prediction.”

If confirmed, this measurement suggests that the standard model may need to be updated.

All eyes are now on the Compact Muon Solenoid detector based in the Large Hadron Collider, which hopes to publish its own measurement of the W boson early next year.

Prof David Toback, who is the project co-spokesperson, told BBC News that the “shocking” new results could lead to the development of an entirely new and more plausible theory of how the universe works.

“If the results are verified by other experiments, the world is going to look different. There has to be a paradigm shift,” he said. “The hope is that maybe this result is going to be the one that breaks the dam.”

Almost exactly a year ago, new evidence from Fermilab suggested that a tiny subatomic particle called muon could break the known laws of physics, hinting at the existence of a fifth force of nature.

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Vish Gain is a journalist with Silicon Republic