A particle that is too heavy disturbs the physics

Mathilde Fontez, editor-in-chief of the science magazine epsilonreminds us of a discovery that was announced a few days ago and which has caused quite a stir in physics.

franceinfo: On measured the mass of a particle and it is too high, which could mean that the theories of matter have to be rewritten?

Mathilde Fontez: Yes, the mass value that has been measured in the past, and most importantly predicted theoretically, was around 80,357 megaelectronvolts. And the mass, just released by a collaboration of nearly 400 physicists, is 80,443.5. So we agree, the difference is not huge: just 0.09%. But these measurements are accurate: that difference is enough to say there’s a problem, that we didn’t understand something.

Is it a particle of matter that has been measured?

It is an elementary particle called the W boson: a particle of the same family as the photon, the particle of light. Aside from not transmitting electromagnetism, the W boson transmits a nuclear force: it is involved in radioactivity. It was discovered in 1983 and has been studied a lot since then, in particle accelerators, those big tunnels where particles are spun at the speed of light so that they explode against each other, creating secondary particles that can be studied.

It is data of this type 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 determine its mass.

So the W boson is too heavy?

A little too heavy yes. So we could say that we were simply wrong about this mass, that it doesn’t change much. Except that in the theory of matter – this theory is called the standard model – all properties of the particles are described and related to each other. If we got the mass of the W boson wrong, that means the theory is wrong, there’s a problem. And that’s great news!

Why good news?

Because physicists know that the Standard Model is incomplete. And they’ve been searching 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 boson to find a loophole to unravel this mystery.

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