The muon, a revolutionary particle that agitates the world of physics

The muon, a revolutionary particle that agitates the world of physics
The muon, a revolutionary particle that agitates the world of physics
DISCOVERY – In physics, there is a fine line between the scientific revolution and the dead end of statistical error. Particular. It is on this ridge line that physicists interested in muons hike, since the publication on Wednesday of new results holding the international community in suspense.

In front of the measuring devices of scientists at Fermilab, in the United States, the muon, a tiny subatomic element, a cousin of the electron, has disobeyed the laws of the “standard model”, the theoretical bible which governs our understanding of the world.

With its strange behavior, the muon is a star in the world of physics. A heavyweight, literally and figuratively. The muon weighs 200 times heavier than an electron, a closer similar particle. And above all, under the spotlight, here the magnetic field of the Fermilab laboratory, the element adopts a behavior totally different from what is expected by the standard model, a sort of large theory which governs the infinitely small.

An unknown universe

With the precaution of rigor in the profession, scientists are moved by this discovery, a fragile indication of the presence of a hitherto unknown universe in the world of atoms. “It’s kind of like landing on Mars, the timing is right,” said Chris Polly, a physicist at Fermilab who has worked on muons all his life.

Chris Polly and his colleagues’ press conference brought together 5,000 scientists and curious people from all over the world on Wednesday. The experiment was to clarify and confirm results already observed 20 years ago, during an experiment called Muon g-2. The Fermilab experiment has a one in 40,000 chance of being an error (sigma 4.1).

This probability is better than that obtained in the 2000s, but it is not yet precise enough for the infinitely small. In this scientific world, the error threshold must be less than one in 3.5 million (5 sigma) chance for a discovery to be considered significant.

“Today is an extraordinary day, long awaited, not only for us, but for all physicists around the world,” said Graziano Venanzoni, spokesperson for the Italian National Institute of Nuclear Physics, who collaborated on the study.

What do “physicists around the world” really think? “If it turns out that this is a new physique that is opening up, I would be very excited. I am not in particle physics, I am in a different field, but to have observations which go beyond the Standard Model would be exciting, it would allow us to advance among the multiplicity of hypotheses that were formulated to describe the anomalies of observed measurements ”explains Christine Guerlin, teacher-researcher at the University of Paris VI.

Revolution, not revolution?

Emile Emery, a student at Polytechnique in Master High Energy Physics, makes a good future researcher a point of honor not to get carried away: “There are regular discoveries. They do not all have the same scope. It could simply be an additional precision on the existing model ”. On the same day, another muon study was released in Nature. She reports that the measured anomalies could be due to other factors predicted by the Standard Model.

Revolution, not revolution? Science has still not decided, but the intriguing elements accumulate. Two weeks ago, another study on the muon, this time carried out in Geneva at CERN, shows that another aspect of its behavior, decay, does not respect the standard model of physics,

“We are both excited and very cautious at the same time,” explains Marie-Hélène Schune, a physicist who took part in the CERN study. Two weeks ago, the seminar she organized to present these results was also a hit. The muon and its strange behaviors are sold out. But here too there is doubt about a statistical error. The significance of the experiment is only 3.1 sigma, which is less than the experiment conducted in the United States.

Other studies are in progress, but the process of verifying the anomalies observed is very long. In the case of muon decay, the strange event that Marie-Hélène Schune recorded only occurs once in millions of trials. You have to repeat the operation millions and millions of times to check if it is not an error. New studies should be published this year by CERN, specifies the researcher.

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