Why is the Higgs particle so important?

Most of us have been taught in school or from books that all the materials around us – everything we eat, drink, breathe, all living beings, the Earth itself – is made of atoms. There are about 100 types of them, they are called “chemical elements” and are usually organized in the form of molecules, in the same way that letters can be organized into words. We take these facts about our world for granted, but at the end of the 19th century there were still heated debates about this. Only around 1900, when it became possible to calculate the size of atoms on the basis of several conclusions, and when the electron, the subatomic particle inhabiting the outskirts of atoms, was discovered, the atomic picture of the world finally took shape.

But even today some parts of this picture are not quite clearly visible. Hundred-year-old mysteries remain unsolved. And all this hype about the “Higgs boson” is directly related to these deep questions that are at the very heart of our existence. Soon, the blurry parts of our picture will be able to become clearer and reveal to us details about our world that are still unclear to us.

In school, we were taught that the mass of the atom is mainly due to its small nucleus. The electrons that form a fuzzy cloud around the nucleus add no more than one thousandth of it to this mass. But what they usually don’t tell us, unless we’re into deep physics, is that the size of an atom depends mostly on the mass of the electron. If you could somehow reduce the mass of an electron, you would find that the atoms grew and became more brittle. Reduce the mass of an electron by a factor of a thousand, and the atoms become so fragile that even the heat left over from the Big Bang can destroy them. Therefore, the whole structure and existence of ordinary materials is connected with a seemingly esoteric question: why do electrons have mass at all?

The mass of an electron and its origin has baffled physicists since its first measurement. Many discoveries related to other seemingly elementary particles made in the last hundred years have complicated and enriched this riddle. First, it was found that light also consists of particles called photons, which have no mass at all. Because the atomic nucleus is made up of particles called quarks that have mass. Recently, we have found signs that neutrinos, the elusive particles that flock from the interior of the Sun, also have a mass, albeit a very small one. Therefore, the question about the electron moved into the category of larger questions: why do particles, such as electrons, quarks and neutrinos, have mass, but photons do not?

In the middle of the last century, physicists learned how to write equations, predicting and describing the behavior of electrons. Although they didn’t know where the electron’s mass came from, they found that it was fairly easy to plug this mass into equations by hand, and decided that a full explanation of its origin would come sometime later. But when they delved deeper into the study of the weak nuclear force, one of the four known in nature, they had a serious problem.

Physicists already knew that electric forces were associated with photons, and then realized that the weak force was associated with particles named “W” and “Z”. But at the same time, the W and Z particles had a difference from the photon in the form of mass – they are comparable in mass to the tin atom, more than a hundred thousand times heavier than the electron. Unfortunately, physicists found they couldn’t plug the particle masses W and Z into the equations by hand: the resulting equations gave meaningless predictions. And when they studied how the weak force affects electrons, quarks, and neutrinos, they found that the old way of putting mass into equations didn’t work—it also broke the whole system.

To explain how elementary particles are known may have mass, fresh ideas were required.

This mystery gradually emerged in the 1950s and 1960s. And in the early 1960s, a possible solution appeared – here we meet Peter Higgs and others (Braut, Englert, Guralnik, Hagen and Kibble). They proposed what we now call the Higgs mechanism. Suppose, they say, in nature there is another, yet unknown field – like all fields, it is a kind of substance that exists in all areas of space – non-zero and uniform in all space and time. If this field—now called the Higgs field—is of the right type, its presence will cause the W and Z particles to show mass, and also allow physicists to put the mass of the electron back into the equations. This will still put off the question of why the mass of the electron is what it is, but at least then it will be possible to write equations in which the mass of the electron is not zero!

In the decades that followed, the idea of ​​the Higgs mechanism was tested by various ways. Today, from the most detailed studies of the W and Z particles, it is known that the solution to the puzzle, which appeared due to the weak interaction, lies somewhere in this area. But the details of this story are unknown to us.

What is the Higgs field, how to understand it? It is invisible to us and we do not feel it, just as a child does not feel air, or like a fish does not feel water. And even more – for if, growing up, we begin to be aware of the flow of air around our bodies and feel it with the help of touch, none of our senses give us access to the Higgs field. Not only can we not detect it with the senses, we cannot do it directly and with scientific instruments. So how can we be sure it exists? And how can we hope to learn anything about him?

The analogy between air and the Higgs field works well in the following example: if either of these two media is disturbed, they vibrate and create waves. It is easy to create such waves in the air – you can shout or clap your hands – and then our ears will detect these waves in the form of sound. In the Higgs field, waves are harder to create and harder to observe. This will require a giant particle accelerator, the Large Hadron Collider. And to detect them, you need scientific instruments the size of a house, like ATLAS or CMS.

How does it work? Clapping your hands is sure to create loud sound waves. The collision of two high-energy protons at the LHC will create very quiet Higgs waves, moreover, optional – only one collision will lead to this ten billion. The resulting wave will be the quietest possible wave in the Higgs field (in technical terms, one quantum of this type of wave). We call this wave the “Higgs particle” or the “Higgs boson”.

Sometimes the media refer to it as the “god particle”. This term was coined by a publisher to sell his book better, so it comes from advertising, not science or religion. Scientists do not use this term.

Creating the Higgs particle is only part of the process, and relatively easy. Much harder to find it. Sound waves travel freely from your palms across the room to the other person’s ear. And the Higgs particle disintegrates into others faster than you can say “Higgs boson.” In fact, faster than it takes light to travel the diameter of an atom. ATLAS and CMS only carefully measure the remnants of the exploding Higgs particle and try to rewind what happened, like detectives unraveling the evidence, to determine whether the Higgs particle could be the source of these remnants.

In fact, it’s even more difficult. It is not enough to create a single Higgs particle, since its remnants cannot be distinguished. Often, the collision of two protons results in debris resembling what results from the decay of a Higgs particle. So how do we establish that the Higgs particle originated? The key is that although Higgs particles are rare, their fragments appear quite regularly, while other processes occur frequently but more randomly. In the same way that your ear can recognize a singing voice even through heavy radio interference, experimenters can make out the regular ringing of the Higgs field amid the random cacophony created by other similar processes.

It turns out to be extremely complex and difficult to pull off. But it was done as part of a triumph of human ingenuity.

Why bother with such Herculean feats at all? Because of the extreme importance of the Higgs field to our very existence. This importance can only be matched by our ignorance about its origin and properties. We don’t even know if one such field exists; there may be several. The Higgs field can itself be a composite of other fields. We don’t know why it is non-zero, and we don’t know why it interacts differently with different particles, and gives, say, an electron, a mass that is not at all the same as the mass of an up quark. Since mass plays an important role not only in determining the size of atoms, but also in many other properties of nature, our understanding of the universe and ourselves cannot be complete and satisfactory while the Higgs field remains so mysterious. The study of Higgs particles – waves in the Higgs field – will give us deep knowledge about the nature of this field, just like you can learn about air from sound waves, about stone from studying earthquakes, and about the sea from watching waves on a beach.

Some of you will probably (and rightly) ask: this is all very inspiring, but what benefit can it bring to society in a practical sense? You may not like the answer. History shows that the social benefits of research on fundamental questions may not materialize for decades, even a century. I suspect that today you used a computer. I doubt that when Thompson discovered electrons in 1897, anyone around him could have guessed how much electronics could change society. We do not hope to present the technologies of the next century or how the seemingly esoteric knowledge gained today may affect the distant future. Investing in fundamental research is always a bit of a gamble, but based on knowledge. At worst, we learn something profound about nature that has unexpected consequences. Such knowledge, though not of monetary value, is priceless in both senses.

For the sake of brevity, I have simplified a few things. It didn’t have to be that way. It was possible that the waves in the Higgs field would be undetectable – it could be like trying to create waves on an asphalt lake or in thick syrup. The waves could have died out before they were fully formed. But we know enough about the particles of nature to know that such an option would only be possible if there were other undiscovered particles and interactions – and some of them could definitely be found at the LHC. Or the Higgs particle(s) could exist, but in such a way that it would be much more difficult to produce, or it could disintegrate in some unexpected way. In all such cases, it could be several more years before the Higgs field began to reveal its secrets. So we were ready to wait, although we hoped that we would not have to explain all these difficulties to the media.

But we were worried in vain.

The discovery of the Higgs particle is a turning point in history. A triumph for those who proposed the Higgs mechanism and those working for the LHC, ATLAS and CMS. But it does not mean the end of our mysteries related to the mass of known particles – it is only the beginning of our hope to solve these mysteries. In the future, energies and collisions at the LHC will increase, and ATLAS and CMS will comprehensively and systematically investigate the Higgs particle. What they learn may allow us to solve the mysteries of this mass-producing ocean in which we all swim, and guide us further along an epic journey that began more than a hundred years ago, which may take decades and centuries more, and extends beyond our present day. horizons.

Original by Matt Strassler
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