10 years since the discovery of the Higgs boson. What do scientists still not know about the particle

(ORDO NEWS) — Physicists around the world have celebrated the tenth anniversary of the press conference announcing the remarkable discovery of modernity.

However, many properties of the “particle of God” are still a mystery to scientists. Why is the Higgs boson called that?

Why is it so important to science and our understanding of the universe? And how does it affect the stability of the universe? The answers to all these questions are in our material.

The scientific editors of Vesti.Ru followed the live announcement with interest. In terms of significance, this achievement can only be compared with the creation of CRISPR gene editing technology and the long-awaited detection of gravitational waves around the same years.

Monday, July 4, 2022, marks the 10th anniversary of the famous press conference at CERN, the main European laboratory for studying the foundations of the universe. 10 years ago, scientists announced the long-awaited discovery of the Higgs boson, a particle often referred to in the media at the time as the “god particle”.

A striking example of the power of international cooperation made it possible to discover a particle that had previously only existed in the calculations of theorists.

The discovery of the elusive particle filled the last gap in the Standard Model of elementary particles – the best physical description of particles and their interactions to date – and opened a window into the so-called New Physics.

With this discovery, in 2012, the experimental detection of elementary particles predicted by the Standard Model was actually completed.

Many then hoped that a new era in physics would now begin, which would allow discovering phenomena that could not be explained using the Standard Model, and testing new exotic theories that explain how the universe works.

However, so far this has not happened. Although scientists have since carried out more than one cycle of launching and many years of operation of the Large Hadron Collider (LHC) and made many other important discoveries during the collisions of protons and heavy ions inside the giant ring of the LHC.

Scientists have published 350 scientific papers on the Higgs boson. However, many properties of the “God particle” still remain a mystery to them.

5 things physicists have learned

The mass of the Higgs boson is 125 billion electron volts.

Why is the mass of a particle not measured in kilograms? The fact is that the mass of such small and elusive objects is easier for physicists to express in units of energy. Let us recall that mass and energy are related by the famous formula E=mc2.

In the 1960s, British theoretical physicist Peter Higgs and his colleagues suggested that what is now called the Higgs field could explain:

– why a particle of light of a photon, a carrier of electromagnetic interaction, has no mass,

– why the gluon, the carrier of the strong force, has no mass,

– why W- and Z-bosons, carriers of the weak interaction, have such a high mass (for elementary particles).

W- and Z-bosons are almost 100 times heavier than a proton and are comparable in this indicator to the giants of the world of chemical elements – technetium and rubidium.

The special properties of the Higgs field allowed the same mathematics to explain the masses of all particles, and it became an integral part of the Standard Model. But the theory made no predictions about the mass of the Higgs boson, and thus when the LHC would be able to create it.

Nevertheless, the particle manifested itself much earlier than expected. The LHC began collecting data in search of the Higgs boson in 2009, and the ATLAS and CMS detectors actually caught it by the tail as early as 2012.

The detectors observed the decay of only a few dozen Higgs bosons into photons, W and Z bosons. They were indicated by a jump in the data at 125 billion electronvolts (or gigaelectronvolts, GeV), which is about 125 times the mass of a proton.

The Higgs boson’s mass of 125 GeV puts it in the sweet spot, which means the boson decays into a wide range of particles at a frequency high enough to be observed in experiments at the LHC, says Matthew McCullough, a theoretical physicist at CERN.

“It’s very strange and probably coincidental, but it just so happens that [at this mass] you can learn a lot about the Higgs boson,” the scientist adds.

What else did physicists learn?

The Higgs boson is a particle with zero spin

Spin is a quantum mechanical property of a particle, which is easiest to imagine if we compare the particle to a magnet.

But, to avoid getting too deep into particle physics, let’s just say that all known fundamental particles had spin 1/2 or 1. However, theories predicted that the Higgs boson should be unique in this respect, since it has zero spin ( also scientists correctly predicted that it has zero charge).

In 2013, experiments conducted at the LHC made it possible to study the angle at which photons produced by the decay of the Higgs boson flew into detectors. The scientists used this information to show with a high probability that the Higgs boson has zero spin.

By the way, until this was demonstrated, few physicists were ready to call the discovered particle the Higgs boson, explains Ramona Gröber, a theoretical physicist at the University of Padua in Italy.

The properties of the Higgs boson excluded some of the theories that complemented the Standard Model.
Physicists know that the Standard Model does not fully describe what happens in the universe.

So, it doesn’t actually work at high energies and can’t explain key observations like the existence of dark matter or why there’s so little antimatter in the universe.

So physicists have come up with extensions to the model that take this into account. The discovery of the Higgs boson mass of 125 GeV has made some of these theories less attractive to researchers, Gröber says.

However, due to the mass of 125 GeV, not many theories turned out to be untenable.

“We have a particle that is more or less compatible with everything [in the arsenal of physicists],” said Freya Blekman, a physicist at the German Electron Synchrotron DESY.

The Higgs boson interacts with other particles, just as the Standard Model predicts.

According to the Standard Model, the mass of a particle is determined by how strongly it interacted with the Higgs field.

Although the boson, which is like a ripple in the Higgs field, does not play a role in this process, the rate at which Higgs bosons decay into or are produced by any other particle gives an idea of ​​how strongly that particle interacts with the Higgs field.

Experiments at the LHC confirmed that, at least for the heaviest particles, most often produced by the decay of the Higgs boson, the mass of the particles is proportional to the interaction with the field. And that was a remarkable achievement for a 60-year-old theory.

How particles gain mass by interacting with the Higgs field, or the Braut-Engler-Higgs mechanism.
Theorists Robert Braut, François Engler and Peter Higgs suggested that particles acquire mass by interacting with the “Higgs field”.

Immediately after the Big Bang, the Higgs field was zero, but as the universe cooled and the temperature dropped below a critical value, the field spontaneously increased, so that any particle interacting with it gained mass.

The more the particle has interacted with this field, the heavier it is. Particles like a photon that have not interacted with it have no mass at all.

In total, the particles “communicated” with the Higgs field for about 10-12 seconds. Before that, they had no mass and traveled through space at the speed of light.

Like all fundamental fields, the Higgs field has an associated particle, the Higgs boson. The Higgs boson is the visible manifestation of the Higgs field, similar to a wave on the surface of the sea.

The universe is stable, but only for now

Calculations using the mass of the Higgs boson have shown that the universe can only be stable for a short period of time, and that there is a vanishingly small chance that it can go into a lower energy state – with catastrophic consequences for everything.

Unlike other known fields, the Higgs field has a lowest energy state above zero even in a vacuum, and it pervades the entire universe.

According to the Standard Model, this so-called ground state of the system depends on how the particles interact with the field.

Shortly after physicists determined the mass of the Higgs boson, theorists used this value (along with other measurements) to predict that there was also a lower and more favorable energy state for the universe.

Let’s try to draw an analogy. We all want peace sometimes. So, the Universe, in a sense, is still bouncing on one leg or, if you like, firmly standing on two legs. But in principle, she would like to sit down. That would make her feel more comfortable.

However, according to McCullough, the transition to another even lower energy state will require the universe to overcome a huge energy barrier. Relatively speaking, in order to sit down, the Universe will first have to run a marathon.

The probability of such an outcome is so small that physicists believe the following: it is unlikely to happen on the time scale of the life of the universe.

“Our end of the world will come much sooner for other reasons,” says McCullough.

Not very inspiring, but honest. At least in terms of science.

5 things scientists still want to find out

Can we make measurements of the Higgs boson more accurate?

At the moment, the properties of the “God particle” correspond to those predicted by the Standard Model, but the measurement error is about 10%.

It’s as if we found out that a person’s “height” is 150 cm plus or minus 15 cm. That is, he can be both 165 cm tall and 135 cm tall and everything in between. Quite a noticeable spread, isn’t it?

In general, the available data, despite all the impressive capabilities of the world’s largest experimental facility (which is the LHC), is not enough. They do not reveal the subtle differences predicted by new physical theories that differ only slightly from the Standard Model.

What can help reduce this error? New data collected during new collisions. Both those that are still being processed, and those that will be received only in the future.

So far, the LHC detectors have collected only one-twentieth of the total amount of information it is designed to collect. And scientists will have to process all this data for quite a long time.

It will be possible to see hints of New Physics, that is, those theories that will allow us to explain what the Standard Model does not explain, in new, more accurate studies.

Does the Higgs boson interact with lighter particles?

So far, the interactions of the Higgs boson with other particles have seemed to fit the Standard Model. However, physicists have seen how it decays only into the heaviest particles.

Now physicists want to test whether it interacts in the same way with particles from lighter families.

In 2020, the CMS and ATLAS detectors observed one such interaction, the rare decay of the Higgs boson into a second-generation electron cousin called a muon.

While this suggests that the relationship between mass and force with the Higgs field holds true for lighter particles, physicists need more data to confirm this.

Does the Higgs boson interact with itself?

The Higgs boson has mass, so it must interact with itself. But the neutrino in this sense is much more elusive.

However, such interactions for example, the decay of an energetic Higgs boson into two less energetic ones are extremely rare, because all the particles involved in this process are very heavy.

Scientists hope to find hints of such interaction after the planned upgrade of the LHC in 2026. However, for convincing evidence of this, physicists will probably need to build an even more powerful collider.

The speed of this interaction with oneself is critical to understanding the universe, says McCullough.

The probability of such an interaction is associated with a change in the potential energy of the Higgs field near its minimum, which describes the conditions immediately after the Big Bang. Thus, knowledge of this process can help scientists understand the dynamics of the early universe.

Gröber notes that many of the theories that try to explain how matter in the universe somehow became more common than antimatter require Higgs bosons to interact with each other.

However, in this they differ from the prediction of the Standard Model by as much as 30%.

“I can’t even begin to express how important [these measurements] are,” says McCullough.

What is the lifetime of the Higgs boson?

Physicists want to know the lifetime of the Higgs boson how long it lives on average before it decays into other particles.

And the point is not in the number itself, as such, but in the fact that any deviation from the predictions can indicate an interaction with unknown particles, such as those that make up dark matter. However, its lifetime is too short to be measured directly.

To measure it indirectly, physicists look at the spread of a particle’s energy over multiple dimensions (quantum physics suggests that the uncertainty in a particle’s energy must be inversely proportional to its lifetime).

In 2021, physicists working with data from the CMS detector made the first rough measurement of the lifetime of the Higgs boson: 2.1×10–22 seconds.

This result shows that the lifetime is consistent with the Standard Model.

How accurate and how accurate are exotic predictions?

Some theories that extend the Standard Model predict that the Higgs boson is not a fundamental particle. That is, it, like, for example, a proton, consists of other constituent elements (quarks).

Others suggest that there are multiple Higgs bosons, we just can’t tell them apart yet because they all behave the same way. However, they differ, for example, in charge or spin.

New experiments at the LHC, which we will discuss in detail in the near future, will help to understand whether the Higgs boson is really a particle of the Standard Model.

Also, new experiments on the collision of particles will reveal the properties predicted by other theories. So, physicists will look for decays into forbidden combinations of particles in the data.

It turns out that the unplowed Higgs field is still waiting for a lot of tests and new researchers.

10 years since the discovery of the Higgs boson What do scientists still not know about the particle 2
Peter Higgs was at the forefront of the creation of the LHC. In this picture, he is standing next to the CMS detector, which at that time was under maintenance

Why “Higgs boson” and why “God particle”?

Why the Higgs field and the boson were named after the British physicist is understandable.

But why “particle of God”? This name was coined by the Nobel laureate Leon Lederman, who wrote the book “God Particle: If the Universe is the answer, then what is the question?”. American and British publishers love big titles, even if they don’t get the point across.

By the way, Lederman himself suggested that the Higgs boson be called a goddamn particle. But this word has a strong negative connotation in English, which is probably why the editor rejected this option.

Since, as we have already said, the Higgs boson determines the masses of other particles and a kind of materiality of the whole world known to us, the “God particle” looks quite natural.

True, scientists themselves prefer another ironic version – the “champagne bottle boson” – because of the similarity of the potential of the complex Higgs field with the bottom of a standard bottle of sparkling wine.

10 years since the discovery of the Higgs boson What do scientists still not know about the particle 3
An example of the Higgs field potential for a fixed value of one of the variables.
Illustration by Gonis

Was the discovery of the Higgs boson the pinnacle of high energy physics at CERN?

As, we hope, became clear from our long story: no. There are many more discoveries ahead.

But I would like to note how huge the contribution of the countries-creators of the LHC and CERN in particular to the popularization of elementary particle physics is.

Before this huge, complex, very expensive and so necessary machine for understanding the Universe was built, the general public was much more worried about whether the “unfortunate physicists” would create a black hole in the LHC, which would then swallow the Earth and all living things.

However, over the years, scientists themselves, representatives of the press services of scientific organizations and journalists invited by them were able to create an adequate idea of ​​what was happening at the LHC in ordinary people.

The announcement of the discovery of the Higgs boson was watched by thousands of people around the world. And they sincerely wanted to understand why the “particle of God”? Perhaps if such an impressive work had not been done then, we would not have seen headlines like this in non-specialized publications today.

At the same time, the current situation in the world (and in science) does not allow us to hope that in the coming years cooperation between countries will resume with the same force as before.

Yes, the Large Hadron Collider is preparing for new records, and we will also write about this in the coming days. However, Russia has actually ceased to be a full-fledged partner of CERN, which means that our scientists with their brilliant competencies will no longer join the ranks of European laboratories.

The destruction of former ties is recognized even overseas, where scientists also had to concentrate on other projects.

At the same time, Japan is unlikely to build an International Linear Collider, and China’s plans for the China Electron-Positron Collider may be too ambitious even for China.

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