SCIENCE – This could well be a great physical discovery, changing all the laws known so far. Physicists have discovered that one of the 17 elementary particles known to physics, the W particle, is 0.1% heavier than expected. Mentioned in the magazine Science on April 7, this new measurement of the particle accelerator of the laboratory Fermilab in the United States (or CDF), specializing in the physics of particles high energies.
If this mass difference seems small, however, it could foreshadow a revolution in fundamental physics. “It would be a complete shift in the way we see the world,” possibly even contradicting the discovery of the… Higgs boson in 2012 in terms of importance, explains for Quanta magazine, Sven Heinemeyer, a physicist from the Institute of Theoretical Physics in Madrid. Indeed, it would entail the first major rewrite of the laws of quantum physics in half a century.
Specifically, if the mass of this particle is actually heavier than previously estimated, it changes all physical laws. Imagine a Tetris game. Each particle forms a piece and forms a perfect whole. Only, if one of the parts gets bigger, the whole no longer works. It is therefore necessary to rearrange the whole, changing the shape of the parts, or even adding new ones to find the exact balance.
In this way, if the W particle has a slightly heavier mass, it means that the current laws of physics are no longer good, and that a new model must be found that explains the workings of the universe, from the stars to the everyday objects.
Indeed, everything around us is made up of subatomic particles of matter. They are divided into two families: quarks (such as neutrons and protons, elements that form the nucleus of atoms) and leptons (such as electrons† In total, 12 elementary particles are listed today, which form the category of fermions.
These matter particles interact with each other. To do this, another type of particle intervenes: the particles of interaction. They are called bosons and are four in number, not counting the exception of the Higgs boson (or god particle). It is the particles of interaction that are at play in three of the fundamental forces.
In all, there are four forces that define the Standard Model of fundamental physics: the strong force, the weak force, the electromagnetic force, and gravity. If the first three interact with each other, gravity is (for now) a special case.
Though it’s the force we’re most familiar with, physicists have struggled to find a place for it in the Standard Model, though the particle that carries gravity (theoretically the “graviton”) has not yet been observed. This is why it is not present in the table below:
The particle that interests physicists here is called the W boson, one of the sources of the weak force. To calculate the mass, the physicists relied on an analysis of about 4 million W bosons produced in the Tevatron (name of the CDF particle accelerator) between 2002 and 2011.
This one discovery comes at a time when the physics community is hungry for flaws in the Standard Model of particle physics. Indeed, the Standard Model is known to be incomplete, leaving several great mysteries unsolved, such as the nature of dark matter.
“It’s monumental work,” said Frank Wilczek, a Nobel Prize-winning physicist at the Massachusetts Institute of Technology. “Overall, I feel like we’re approaching the point where something is going to break,” El-Khadra said. “We’re getting closer to the time when we can really look beyond the standard model.”
Caution is advised
However, no one is popping the champagne yet. While the new W mass measurement taken in isolation is dramatically different from the Standard Model prediction, other experiments with the W boson have yielded less spectacular results.
For example, in 2017, the ATLAS experiment at the Large Hadron Collider in Europe (a particle accelerator with a circumference of 27 km, the largest and most powerful in the world) measured the mass of the W particle and found that it was only slightly heavier than what the standard model says.
It is important to understand the difference in measurement between the two labs. Indeed, as Guillaume Unal, a physicist at CERN (the lab that houses the Large Hadron Collider), claims, “the W boson must be the same on both sides of the Atlantic.”
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