Shulou(Shulou.com)12/24 Report--

This article comes from the official account of Wechat: SF Chinese (ID:kexuejiaodian), author: SF

According to the latest measurement data released by Fermi Lab, the behavior of μ in the magnetic field is not consistent with the prediction of the standard model. This indicates that there may be some physical phenomena that can not be explained by the standard model, and may even involve a new basic force.

/ tr. by Jon Butterworth (Jon Butterworth)

Translation | Li Shijie

Editor | Chen Qiang

The original article is published in Science focus, No. 01, 2024.

At Fermi Lab near Chicago, an international team of scientists made more accurate measurements of the interaction between muons and the magnetic field, and released the latest results on August 10, 2023.

Physicists are looking forward to the results of this measurement, mainly because of the significant differences between the previous measurements and the standard model of particle physics. One possible explanation for this difference is that there is a fifth fundamental force in the universe. So, is there really a basic force that has not yet been discovered? What can the results of this measurement tell us?

Does the fifth basic force affect the μ-submagnetic moment? We know that there are four known basic forces in nature, namely, gravity, electromagnetic force, strong nuclear force and weak nuclear force.

General relativity accurately describes gravity, while the standard model of particle physics explains the other three fundamental forces. The fifth fundamental force will go beyond the existing framework of physics, so its discovery will be a major breakthrough for physicists to explore the nature of the universe.

Physicists have been eager to make this breakthrough, because although the standard model can explain many physical phenomena almost perfectly, it is not a complete "theory of everything".

For example, the standard model cannot explain gravity. In fact, general relativity and the standard model are incompatible at very high energies. For physicists, any measurement that does not agree with the theory will be seen as a clue that there may be a more comprehensive and explanatory theory.

Fermi's measurements made physicists feel that such a breakthrough might be just around the corner. According to the standard model, the muon is an elementary particle, that is, it is one of the basic units that make up matter. The muon is very similar to the electron, but the mass is about 210 times that of the electron.

In addition to the negative charge, the muon also has an intrinsic angular momentum, which is called spin. According to the laws of physics, the muon produces a tiny magnetic moment, just like a miniature magnetic needle. When the muon is in a magnetic field, its magnetic moment will precede, just like a rotating gyro will wobble. The magnitude of the μ submagnetic moment determines the precession frequency.

In Fermi Lab, physicists feed billions of microns into a storage ring and control them using precisely calibrated electric and magnetic fields, so they can measure the precession frequency of muons in the magnetic field.

The precession frequency of the μ can be calculated very accurately by the standard model. The calculation also involves so-called "virtual particles", which are particles that cannot be detected directly, but appear briefly in quantum fluctuations to interact with the muon, thus changing the magnetic moment and precession frequency of the muon. If the experimental results are not consistent with the prediction of the standard model, it may mean that there is an unknown particle in the process of quantum fluctuation.

One possibility is that this unknown particle is the medium of the fifth fundamental force. This new particle is similar to photons, because photons are the medium particles of electromagnetic force, but the new particles are not included in the framework of the standard model.

The storage ring in Fermi Lab can generate a magnetic field and can be used to accurately measure the precession of muons. (photo Source: Reidar Hahn / Fermilab) from the theoretical and experimental challenges, Fermi Lab's latest measurements of the muon magnetic moment have once again verified the previous measurements. Moreover, the accuracy of this measurement is higher. However, before physicists announce the discovery of the fifth fundamental force, there are two important problems that need to be solved.

First of all, there are still problems in theoretical prediction. The current theoretical predictions are based on a widely accepted calculation method, however, there are other calculation methods that can also give predictions. These predictions are all different, and some are closer to the measured results.

Although the difference between experiment and theory may suggest the existence of some new physical phenomenon, physicists need to further determine what the theoretical prediction is before announcing the existence of the fifth fundamental force.

The second question is more challenging, but also more exciting. If this difference is confirmed, then we can be sure that there are some new physical phenomena at work, even if we don't know exactly what it is.

Ideally, physicists come up with a new theory based on this difference, and the new theory also brings new predictions. If the new theory is really related to a new fundamental force, it can tell us how to find the particles that carry the new fundamental force.

The problem is that physicists must conduct an experiment that can directly detect new particles in order to prove that the new theory is correct. Just like in 2012, physicists used the large Hadron Collider to detect the Peter Higgs boson, proving the theory of Peter Higgs and others.

Other measurement experiments, such as those carried out at the large Hadron Collider, also show phenomena that cannot be explained by the standard model. However, this is also a problem that will inevitably arise in the process of exploration. Sometimes, as we get more data and conduct more in-depth research, these problems tend to disappear.

Fermi Lab will release a more accurate measurement in the near future, while the large Hadron Collider will continue to operate and collect more data. With more accurate experimental data, physicists can more carefully analyze the discrepancies between the measurement results and the theory.

In any case, the magnetic moment of the muon is the earliest and most obvious phenomenon that does not accord with the standard model. This measurement is unlikely to be wrong. This means that if the problem of theoretical prediction is solved, it is likely to show that some new physical phenomenon beyond the standard model does exist, and there may even be the fifth fundamental force.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.