Why are scientists looking for the Higgs boson's closest friend?


Scientists at the world's largest physics experiment have reported the most precise measurement of the heaviest subatomic particle ever known. The discovery may seem esoteric, but it's no exaggeration to say it has implications for the entire universe.

The Greek philosopher Empedocles speculated more than 2,400 years ago that matter could be broken down into smaller and smaller pieces until we were left with air, earth, fire and water. Since the early 20th century, physicists have broken matter into smaller pieces and discovered many different subatomic particles instead – so many that it could fill a zoo.

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Top Quark

Contemporary particle physicists focus instead on 'small' particles, i.e., elusive particles.

More energetic particles often break down into particles with less energy. The greater the difference in energy between a particle and its decay products, the less time the particle will exist in its original form and the more quickly it will break down. According to mass-energy equivalence, the more massive the particle is also the more energetic particle. And the heaviest particle scientists have discovered so far is the top quark.

It is 10 times heavier than a water molecule, about three times heavier than a copper molecule, and 95% heavier than a full caffeine molecule.

As a result, the top quark is so unstable that it can break apart into lighter, more stable particles in less than 10 seconds.-25 Seconds.

The mass of the top quark is very important in physics. The mass of a particle is equal to the sum of masses derived from many sources. An important source for all elementary particles is the Higgs field, which pervades the entire universe. A 'field' is like a sea of ​​energy and excitations in the field are called particles. Thus, for example, an excitation of the Higgs field is called a Higgs boson, just as an electron can be thought of as an excitation of an 'electron field'.

All these fields connect to each other in specific ways. When the 'electron field' interacts with the Higgs field at energies much lower than 100 GeV, for example, the electron particle will gain some mass. The same is true for other elementary particles. (GeV, or giga-electron-volt, is a unit of energy used in reference to subatomic particles: 1 joule = 6.24 billion GeV.) François Englert and Peter Higgs received the 2013 Nobel Prize in Physics for explaining this mechanism.

If the top quark is the heaviest subatomic particle, it is because the Higgs boson interacts most strongly with it. By measuring the mass of the top quark as accurately as possible, physicists can learn a lot about the Higgs boson as well.

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“Physicists are curious about the top quark mass because there is something unique about it,” said Nirmal Raj, a particle theorist and assistant professor at the Indian Institute of Science, Bengaluru. Hindu“On the one hand, it is closest to the mass of the Higgs boson to what would be 'naturally' expected before it was measured. On the other hand, all the other [particles like it] are very, very light, raising the question of whether the top quark is in fact a peculiar species, rather than a 'natural' species.”

the universe as we know it

But the rabbit hole goes even deeper.

Physicists are also keen to study the Higgs boson because it has its own mass, which it acquires by interacting with other Higgs bosons. The important thing is that the Higgs boson is heavier than expected – which means that the Higgs field is more energetic than expected. And because it pervades the universe, the universe can be said to be more energetic than expected. This 'expectation' comes from calculations done by physicists and they have no reason to believe they are wrong. Why does the Higgs field have so much energy?

Physicists also have a theory about how the Higgs field originally formed (at the birth of the universe). If they are right, there is a small but non-zero probability that one day in the future, the field could undergo a kind of self-adjustment that reduces its energy and modifies the universe in a dramatic way.

They know that the field today has some potential energy and there is a way it can become more stable by reducing some of it. There are two ways it can reach this stable state. One way is for the field to first gain some energy and then lose it and then more, like climbing up one side of a mountain and falling into a deep valley on the other side. The other way is if a phenomenon called quantum tunneling occurs, causing the field's potential energy to 'tunnel' through the mountain rather than climbing up the mountain and falling into the valley.

This is why Stephen Hawking said in 2016 that the Higgs boson could signal the “end of the universe” as we know it. Even if the Higgs field is slightly stronger than it is now, the atoms of most chemical elements would collapse, destroying stars, galaxies and life on Earth. But while Hawking was technically correct, other physicists were quick to point out that the frequency of a tunneling event was 1 in 10100 Year.

Mass of the Higgs boson — 126 GeV/c2 (the unit used for subatomic particles) – is also enough to maintain the universe in its current state; anything more and “the end” would follow. Such a finely adjusted value is obviously curious and physicists would like to know what natural processes contribute to it. The top quark is part of the picture because it is the heaviest particle, in a way the closest friend of the Higgs boson.

“Precisely measuring the top quark mass will determine whether our universe will blink out of existence,” Dr. Raj said.

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Discovery of the top quark

Physicists discovered the top quark in 1995 at a particle accelerator called the Tevatron in the US, measuring its mass at 151–197 GeV/c.2The Tevatron was shut down in 2011; physicists continued to analyze the data it collected and updated the value to 174.98 GeV/c three years later2. Other experiments and research groups obtained more precise values ​​over time. On June 27, physicists at the Large Hadron Collider (LHC) in Europe reported the most precise figure yet: 172.52 GeV/c2,

The mass of the top quark is difficult to measure since its lifetime is about 10.-25 seconds. Normally, a particle-smasher will create an ultra-hot soup of particles. If a top quark is present in this soup, it will quickly disintegrate into specific groups of lighter particles. Detectors monitor these events, and track and record their properties when they occur. Finally, computers collect this data and physicists analyze them Reconstruction Physical properties of the top quark.

Scientists learn what to expect at each point in the process based on sophisticated mathematical models and must deal with many uncertainties. Many of the instruments used in these machines also involve cutting-edge technologies; when engineers make them better, the results physicists get are better.

Now the researchers will incorporate the top quark's mass measurement into calculations that inform our understanding of the particles in our universe. Some of them will also use it to search for an even more precise value. According to Dr. Raj, accurately measuring the top quark's mass is also important to know if another particle with a mass close to the top quark might be hiding in the data.

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