Mathilde Fontez, editor-in-chief of the scientific journal Epsilontoday evokes a discovery announced a few days ago that is causing a lot of fuss in the field of physics.
france info: On has measured the mass of a particle, and it is too high, which could mean that the theories about matter need to be rewritten?
Mathilde Fontez: Yes, the mass value measured in the past, and more importantly, predicted by the theory, was about 80,357 megaelectronvolts. And the mass just published by a collaboration of nearly 400 physicists is 80,443.5. So we agree that the difference is not huge: just 0.09%. But these measurements are accurate: this difference is enough to say that there is a problem, that there is something that we have not understood.
Is it a particle of matter that has been measured?
That is an elementary particle called the W boson : a particle of the same family as the photon, the light particle. Besides not emitting electromagnetism, the W boson emits a nuclear force: it participates in radioactivity. It was discovered in 1983 and much studied since, in particle accelerators, these large tunnels in which particles are propelled at the speed of light so that they explode against each other, giving rise to secondary particles that can be studied .
It’s this kind of data that speaks today: data from the Tevatron, an American collider that operated between 1984 and 2011. It took physicists 10 years to process them, extract the signal corresponding to millions of W bosons and find their mass.
So the W particle is too heavy?
A little too heavy yes. So we might say to ourselves that we were just wrong about this mass, that not much is changing. Except that in matter theory – this theory is called the standard model – all the properties of the particles are described, and are related to each other. If we were wrong about the mass of the W particle, that means that the theory is wrong, that there is a problem. And that’s great news!
Why good news?
Because physicists know that the Standard Model is incomplete. And they’ve been looking for clues that might lead them to complete it for decades. In particular, this theory fails to describe gravity — we don’t know how to describe on a microscopic scale the force that makes apples fall from trees and keeps our feet on the ground. It is therefore a great hope that opens today, thanks to the W bosonto find a breach, to unravel this mystery.
