Can ‘raw’ electron particles change the direction of physics? Understanding | Sciences

Before winning the Nobel Prize in 1965, American physicist Richard Feynman was feeling somewhat stagnant in his career. In the second half of the 1940s, he was teaching at Cornell University and thinking about how to “enjoy” physics again, rather than devoting himself to research that did not interest him.

One day, in the university café, a young man caught his attention playing by throwing a plate bearing the Cornell logo into the air. Randomly, the physicist did some calculations and noticed that the logo rotated at twice the speed just like the oscillatory motion (or precession) of the plate in the air – it is easier to visualize precession if we imagine a top rotating around its own axis, tilting from side to side. In other words, Feynman observed that the rotation of the plate was equivalent to twice the precession, in a ratio of two to one.

This got the physicist thinking about the orbits of electrons, and he also remembers his initial research with enthusiasm. The flying saucer thus ended up inspiring the development of the theory of quantum electrodynamics, a concept that helps explain physics in the particle dimension.

“The graphs and all that stuff I won the Nobel Prize for came from wasting time with the advanced board,” the physicist says in his entertaining autobiography. It must be a joke, Mr. Feynmanoriginally published in 1985 and released in Brazil in 2019 by publisher Intrínseca.

More than 70 years later, this initiative movement is still one that scientists around the world are monitoring. But now, instead of a cheap dish, they have a 3.2 square kilometer accelerator, which in 2022 alone received a $260 million investment from the US government: the Fermi National Accelerator Laboratory (Fermilab), located on the outskirts of New York City. Chicago in the United States of America.

It was thanks to him that an experiment involving the international cooperation of 181 researchers, from 33 different institutions, was able to discover strange behavior in a particle called the muon.

The experiment, called Muon g-2 (read “muon g minus two”), helped scientists notice that muons, which are considered “heavy” cousins ​​of electrons, indicate a force that does not appear in “standard” theory. The elementary particle model” is one of the most widely accepted concepts in physics (which helps justify its somewhat humble name).

If these data — announced on August 10th, without peer review yet — prove correct, we may face the emergence of a new physics, that is, a new interpretation of how we interpret reality as we know it.

(Not so) God particle

The universe is rich in secrets. But there are three that keep scientists up at night: (1) the existence of dark energy, (2) the existence of dark matter — stuff that no one has a clue what it is, but together they make up about 95 substances. % of the universe — and (3) where antimatter exists.

According to the theoretical predictions of the English physicist Paul Dirac, every fundamental particle of matter existing in the universe should be accompanied by another similar particle, but with a changed charge, “antimatter.”

For every electron, for example, there must be a pair that is exactly the same, but with a positive charge. This “positive electron” does exist, and is called a positron, and proving its existence won Dirac the Nobel Prize in 1933. The problem is that we are able to observe a much larger number of matter than antimatter in the universe. – If Dirac’s predictions are indeed correct, where are antimatter found?

As British physicist Alex Keshavarzi, of the University of Manchester, who is involved in the Múon g-2 experiment, pointed out in a TEDx talk, “Each of these mysteries — what is dark energy, what is dark matter and why there is an asymmetry between matter and antimatter — can be solved.” If we find a new particle, or a new force of nature, that’s exactly what researchers are trying to do.

The problem is that finding something new requires going against the standard model. This theory was completed around 1970, after intense dedication by many physicists throughout the twentieth century, and it describes very well how the universe, with its 17 fundamental particles, works, as if it were a recipe for how all the forces and particles of the universe interact and interact. He created the matter around us.

“At first, the Standard Model was not taken seriously, due to its rather poor appearance, far from the delightful simplicity of general relativity, Maxwell’s equations or Dirac’s,” Italian physicist Carlo Rovelli explains in the book. Reality is not what it seems (objective). But contrary to expectations, all his expectations came true. For more than thirty years, all particle physics experiments have done nothing but reconfirm this.

The last verification occurred in 2013, creating a public uproar by revealing the existence of the Higgs boson, a particle that, although theoretically predicted, had never been observed up to that point. This particle represents the latest addition to the Standard Model’s sticker album. Not for nothing has it received the nickname “God particle,” a title that is as meaningless as it is inaccurate.

Millions of accuracy

Now, researchers are turning their tools toward muons, already well-known particles that reach Earth through cosmic rays or can be generated in the laboratory — in this case, at accelerators like Fermilab. They look like electrons, but they are 200 times larger and only live for about two millionths of a second.

“Just like electrons, muons act as if they had a small internal magnet. “In a strong magnetic field, the direction of the muon magnet advances or oscillates, just like the axis of a rotating top or a gyroscope,” explains physicist Marcelo Lapolla, professor at the Department of Physics at the University of Paulista. Unesp) in Rio Claro. And a columnist for Galileo. The speed of this motion depends on a property of the muon known as the “magnetic moment,” which physicists abbreviate as “g.”

The expectation, according to the theory formulated by Richard Feynman, is that g will always be equal to 2. But in reality, this value is broken by particles appearing and disappearing all the time. By knowing the particles in the Standard Model, scientists can predict how much g will deviate. They call this difference “g-2”.

The point is that muons are sensitive to all particles, including those we know nothing about. “Muons serve as a window into the subatomic world, and may interact with particles or forces that have not yet been discovered,” Lapolla points out.

Recent data from the Muon g-2 experiment indicate that the muons analyzed interacted with unknown elements, that is, forces or particles outside the Standard Model. This means that it is not covered by the theory that best describes the universe so far. These data reinforce information obtained from an experiment conducted in 2021, at the same Fermi Laboratory – which in turn confirmed the result of another experiment, carried out in 2001, at the Brookhaven National Laboratory (BNL), also located in the United States. States.

The difference is that the result is now more accurate. “The Muon g-2 experiment at Fermilab detected about 21 times the number of muon decays studied in the previous measurement at BNL,” Italian physicist Alberto Luciani, who is involved in analyzing the study information, explains to Galileo. “This larger data sample, analyzed using improved techniques, will reduce the statistical uncertainty by a factor of about 4.5 when all muon decays are analysed.”

According to Luciani, the measurement completed in 2023 analyzed data collected in 2018, 2019 and 2020, about 6.5 times the number of muons used to measure the BNL, and resulted in about 2.5 times better accuracy. Now, the researchers must conduct another round of testing, and plan to release more precise final results in 2025.

Chess of the Gods

Expectations for the completion of the Múon g-2 test are high. “If the need for a correction in the Standard Model is confirmed, it will be one of the greatest discoveries of recent decades,” says physicist Marcelo Lapolla, stressing that it is necessary to wait for new results before celebrating anything. For Luciani, the potential discovery could mean a bubble From new research.

“If measuring the muon magnetic anomaly provides evidence that the current theory, the Standard Model, is incomplete, there will be widespread interest in measuring other relevant anomalies and proposing ‘new physics’ models that predict the observed anomaly and can be tested by additional means.” Experimental measurements,” notes the Italian physicist.

However, in the eyes of some researchers, the excitement surrounding the experiment may be hasty. “Before we realize that there is a gap in the Standard Model, we still have a long way to go, especially regarding theoretical calculations, which are very complex,” believes physicist Sergio Ferraz-Noves, researcher at the Institute of Theoretical Physics from UNICEF. It is a member of the international collaboration that announced the discovery of the Higgs boson in 2013.

“The Standard Model has impressive consistency, and we seem to have got the structure chosen by nature to manage these interactions just right, and I don’t see anything very promising in terms of outright violation of the propositions of this theory.”

However, according to Ferraz, even if the experimental data proves correct, the Standard Model will not lose its grip so easily. “There’s no such thing as invalidating a theory, that’s not how science works,” he explains. Einstein’s relativity, for example, did not invalidate Galileo’s transformations, which were carried out 300 years ago.

“Invalidation” is too strong a word, because you can’t throw the huge number of experimental successes and agreements that the Standard Model has had over these years into the trash. Moreover, you can’t throw away a theory if you don’t have another theory to replace it.

With the support of mathematics, physicists are free to propose new models that always help explain the reality that surrounds us. Thus, as it advances in its discoveries, science expands its boundaries with the unknown. Quoting Richard Feynman, a physicist who could visualize the movements of particles on rotating plates, Marcelo Lapolla recalls: “Nature is an enormous game of chess played by the gods, and we have the privilege of observing it. The rules of the game are what we call fundamental physics, and understanding those rules is our goal.”