What is the Higgs boson and how was it discovered?

Añadido: 2026-05-09

[00:00:00]How was the Higgs boson discovered? In one of our previous videos, we talked about the so-called Higgs mechanism, according to which all elementary particles acquire mass through interaction with a field, also known as the Higgs field. And today we are confident that this is indeed how it works, at least since 2012, when the Higgs boson was discovered during experiments at the Large Hadron Collider. What the Higgs boson is, how it was discovered, and why this discovery caused such a sensation at the time, that is what we will discuss in this video.

[00:00:36]So, the Higgs field is a special field through interaction with which elementary particles acquire mass. We explained how this happens in our previous video.

[00:00:44]However, for a long time the Higgs field remained only a hypothesis that still needed to be tested. And essentially, the only way to test it was to detect the Higgs boson itself.

[00:00:55]The Higgs boson is a quantum or an elementary portion of energy of this field.

[00:01:02]Roughly speaking, the energy of the Higgs field in a given region of space is equal to the mass of the Higgs bosons present in that region of space multiplied by the square of the speed of light.

[00:01:14]To make this fully accurate, one would also need to take into account the kinetic energy of these bosons, but we will not go into such details.

[00:01:23]From the mathematical theory of the Higgs field, the properties of its quantum follow directly, in particular, its mass, 2 to 3 * 10 ^ -25 kg, its spin equal to 0, and other characteristics.

[00:01:37]And if we were to detect a particle with such parameters, we could say with a high degree of confidence that it is indeed the Higgs boson. And if the Higgs boson exists, then one could confidently speak about the existence of the Higgs field itself, made of such bosons. Just as paleontologists can reconstruct an extinct animal from its bones.

[00:01:57]In other words, to confirm the hypothesis of the Higgs mechanism by which elementary particles acquire mass, we needed to detect the Higgs boson.

[00:02:06]Unfortunately, this was not easy. The reason is that, according to the same theory, in our universe today the Higgs field is in a so-called vacuum state with zero energy.

[00:02:17]In one of our previous videos, I mentioned that the phrase zero energy does not mean that the energy is strictly equal to zero. Even in a vacuum state, any field undergoes small fluctuations. What matters here is that the Higgs field in the modern universe is in a state in which Higgs bosons are absent. This is not very surprising, as all fields tend toward their vacuum state. The problem is that we can take other fields out of this state.

[00:02:44]For example, a non-zero electric field can be created by placing in a region of space an object that has an electric charge, because all charged objects are sources of an electric field.

[00:02:56]The Higgs field has no such sources. It always and everywhere exists in a vacuum state, and this is actually beneficial because it ensures that elementary particles always and everywhere have the same mass.

[00:03:11]But for physicists trying to catch the Higgs boson, this became a problem, because it is especially difficult to find a black cat in a dark room when it is not there. In essence, the only way to detect the Higgs boson was to create it artificially. The method to create this particle, as well as essentially any other particle, is known. One must take two other particles, accelerate them using an electromagnetic field, giving them large kinetic energy, and then collide them with each other. The kinetic energy accumulated by the particles is released in the form of new particles. More precisely, any particles whose mass multiplied by the square of the speed of light does not [music] exceed the energy of the collision. And since the mass of the Higgs boson, according to theory, should be on the order of 2 to 3 * 10 ^ -25 kg, producing a Higgs boson requires a collision energy on the order of 125 [music] to 250 giga electron volts. The Large Hadron Collider makes it possible to reach collision energies of up to 6.8 tera electron volts, that is 6,800 [music] giga electron volts. Therefore, if one runs the collider and waits long enough, one can be confident that Higgs bosons will indeed be produced in the collisions. But how do we know that? The Higgs boson is an extremely unstable particle with a lifetime of only 10 ^ -22 seconds. However, one can detect the decay process of the Higgs boson through the products of that decay.

[00:04:45]There are many decay channels of the Higgs boson, but the most interesting is the decay into two photons, whose total energy must be exactly equal to the mass of the Higgs boson.

[00:04:56]That is, something on the order of 100 to 200 giga electron volts. However, there was a complication. In proton collisions at the Large Hadron Collider, many different particles are produced, including ones more massive than the Higgs boson.

[00:05:11]These particles also decay quickly, and during their decay, they can emit photons or other particles that themselves decay into photons. In addition, charged [music] particles emit photons, including high-energy ones, as so-called bremsstrahlung radiation, when they slow down after being produced due to interactions with other particles.

[00:05:33]In other words, if we simply turn on the collider and measure the energies of the outgoing photons, [music] we will observe photons with a wide range of energies, including energies on the order of 100 to 200 giga electron volts, and far from all of them will be related to the Higgs boson.

[00:05:51]But the key point is that the Higgs boson would produce not just photons in the range of 100 to 200 giga electron volts, but photons with a strictly defined energy somewhere within that range. Without Higgs bosons, the photon energy spectrum, that is, the frequency with which photons of a given specific energy are detected at the collider, would look smooth. But if the Higgs boson exists, a peak should appear on this curve corresponding to an energy equal to the mass of the Higgs boson multiplied by the square of the speed of light. Thus, by looking at a single photon, we cannot say, "This photon was produced by the decay of a Higgs boson."

[00:06:30]But by analyzing a large number of photons and constructing their spectrum, we can detect the existence of the Higgs boson through its effect on the statistical distribution of photon energies. The difficulty is that Higgs bosons were not produced in every collision. The probability that a Higgs boson would be produced in a given collision was extremely small, on the order of 3 * 10 ^ -10. In experiments at the Large Hadron Collider, a Higgs boson is produced roughly once per several billion collisions. Furthermore, not every Higgs boson decays into two photons. There are other decay channels.

[00:07:08]And since we rely on statistical methods, we need to produce a large number of Higgs bosons so that the photons generated by their decays make a noticeable contribution to the spectrum.

[00:07:19]As a result, collecting sufficient statistics took about 1.5 to 2 years during 2011 and 2012. In the process, scientists carried out approximately 10 ^ 14 to 10 ^ 15 proton-proton collisions, spending on accelerating the protons roughly 3 to 4 * 10 ^ 15 joules of energy, about as much as a small city consumes in a month. The outcome of all this effort was a small bump in the photon energy spectrum, which was interpreted as evidence for the existence of the Higgs boson with a rest energy of 125 giga electron volts and a mass of 2.2 * 10 ^ -25 kg.

[00:08:04]But does this small bump on the graph really mean the discovery of the Higgs boson and confirmation of our understanding of why elementary particles have mass? Let us carefully distinguish what we know for certain from what we only assume. The experimental results clearly indicate the existence and nature of some particle with a mass of 2.2 * 10 ^ -25 kg, which is capable of decaying into two photons. We do not know of any other particle with such a mass, and we have no model that predicts the existence of particles with such a mass and such properties, apart from the theory of the Higgs field. That is why we consider this to be the quantum of the Higgs field, >> [music] >> and therefore conclude that such a field exists. However, if one insists on absolute rigor, one may ask, "Could the particle we have detected be not the Higgs boson, but something else that we did not anticipate, simply because we had no theories predicting its existence?" Physicists, even if reluctantly, must answer, "Yes, in principle, this is possible." Similar situations have occurred in physics before. In 1934, the Japanese physicist Hideki Yukawa developed the first theory of the strong nuclear interaction, which binds protons and neutrons into atomic nuclei. Among other things, this theory predicted the existence of a particle with a mass of about 2 * 10 ^ -28 kg, lighter than a proton, but heavier than an electron, that is, possessing an intermediate mass, which is why it was called a meson, from a Greek word meaning in between. Just 3 years later, Carl Anderson and Seth Neddermeyer, studying cosmic rays, discovered a particle with a mass of approximately 1.8 * 10 ^ -28 kg. Here it is, Yukawa's meson, physicists initially thought. But it turned out that the meson discovered by Carl Anderson and Seth Neddermeyer was not the meson of the strong nuclear interaction at all, but a completely different particle, a heavier relative of the electron. Today, we call these particles muons, [music] and we know that they have nothing to do with the strong nuclear interaction. The real meson predicted by Hideki Yukawa was discovered much later, only in 1947.

[00:10:23]Today, we call such particles pions, and it is fortunate that it was eventually discovered, because otherwise physicists would have had to discard a theory they had already declared experimentally confirmed.

[00:10:35]Could something similar be happening here?

[00:10:38]Purely theoretically, yes. Although in practice, it is unlikely.

[00:10:43]We expected to find a particle within a certain mass range, and we found it.

[00:10:48]Just as importantly, we found only one particle in this mass range, rather than two as in the meson story, or even more.

[00:10:56]Therefore, we have strong grounds to say that the particle we have discovered is indeed the Higgs boson.

[00:11:03]At least until we obtain truly compelling reasons to believe that it is something else. And if such reasons appear, I will certainly talk about them on our channel.

[00:11:13]For now, we work with what we have, and we interpret the results of experiments at the Large Hadron Collider as confirmation of the existence of the Higgs field. That is all for today. All the best to you, friends, and see you again in our next videos.