2023-08-16 12:32:00
Physicists have come within a whisker of the discovery of the decade: they observed a phenomenon not foreseen by the most successful theory of their discipline. How to revise it and imagine that nature had until now hidden new particles and new forces from the sharp gaze of scientists.
The phenomenon in question is the behavior of the muon, a particle two hundred times heavier than the electron and carrying, like it, a negative electric charge, which does not turn as round as the theory predicts. More exactly, the reaction of this particle to the application of a magnetic field turns out to be higher than in the calculations. Not much, about 0.0002% more, which is enough to think of the manifestation of new, as yet unknown, physics. And so exciting.
A theory itself uncertain
The result was announced on August 10 by the international collaboration Muon g − 2 (« g − 2″ referring to the magnetic moment of this particle, which governs how it interacts with a magnet). It is twice as accurate as the one announced in April 2021thanks to almost four times more data, obtained at the Fermilab laboratory in Chicago by a group of 180 researchers from seven countries.
Read also: Article reserved for our subscribers Muon rotations electrify the physics community
Another progress obtained in two years: the statistical confidence in the result is also stronger. At the time, researchers estimated that the difference between theory and experiment could very well be due to chance, with a chance in 40,000. Like six dice that would fall on 6 on the first throw. This time, with more “dice rolls”, the chance would be reduced to one in a million and a half (like getting eight 6s with eight dice at once…). In this discipline, this criterion is sufficient to proclaim a discovery and to affirm that the experiment does not stick to the theory.
Except that… the theory itself is not certain! Admittedly, the theory which describes the three forces acting on elementary particles, the standard model, is robust and has never been faulted. But it gets more complicated when you want to calculate what is happening in detail. And the details concerning the magnetic moment are not lacking because, to predict its value, it is necessary to take into account the fleeting and numerous interactions of the muon with a set of other particles. Two methods, for the moment incompatible, have been proposed to achieve this. The first is based on data obtained by other experiments on other particles. As if, to predict the mass of a planet, we used the orbit of other stars. The second is based on clever but very long numerical simulations.
You have 54.33% of this article left to read. The following is for subscribers only.
#muon #particle #agitates #physicists #talking