Particle Physics

By | July 15, 2020

What is Quark Confinement?

In this article we will talk about an interesting phenomenon of particle physics “Quark Confinement”, also see if we can find free quarks. And how the Strong Nuclear Force has a unique attitude towards other forces.

A previous article talked about the color charge of quarks, how some issues arose during the application of poly-exclusion principals on some headrons, and by solving them, the reality of this color property of quarks became clear to us. The color charge of quarks is exactly the same as that of many particles such as electrons. And because of this electric charge, these particles interact with each other through electromagnetic force. Although quarks also have an electric charge and can interact with electromagnetic forces, there is another type of charge on quarks due to their color property which we call color charge. And because of this color charge, quarks also interact with each other and we interpret this interaction as strong nuclear interaction or strong nuclear force.

We saw one thing at the end of the article on the color charge of quarks. Suppose if we look at electromagnetic interactions, here if we bring two particles with the same electric charge, such as two electrons, close to each other. Push away Quantum electrodynamics (QED) illustrates this phenomenon with the exchange of a virtual photon between two particles. That is, the exchange of photons between the two particles leads to the transfer of momentum, and in order to conserve this momentum, the two particles move in opposite directions. Now when a strong interaction occurs between two quarks.

So Quantum Chromosome Dynamics (QCD) describes it the same way, but this time the particle exchanged between quarks is not a photon, but a gluon, which is the force carrier of a strong nuclear force. There is a difference between these two types of interactions and this difference is due to the difference in the basic properties of the boson particles exchanged in these two interactions. The force carrier photon of the electromagnetic force does not have an electric charge, while the force carrier gluon of the strong nuclear force also has a color charge. This is why the electromagnetic charge of the particles does not change during photon exchange during electromagnetic interaction, only the momentum is transmitted. In contrast, during strong nuclear interactions, the gluon carries a color charge of its own, so it also changes the color of the quarks during the exchange. Not only that, but this feature of Gluan introduces us to this interesting phenomenon of particle physics which we call “Quark Confinement” which is the main topic of this post.

In particle physics, we study many particles. These include the popular particles electrons, neutrons, protons, and many types of mesenchymal particles. We can also use these particles for individual study. For example, if an electron is present inside an atom or an independent electron, we can find it in both cases. But to this day we have not been able to get quarks freely. We always get them in groups. If three quarks exist in groups, they will form baryons, and if two quarks (quarks and anti-quarks) form groups, they will become meson particles. Groups of quarks formed in this way are called hadrons. This has also been discussed in an article. I will give the link below.

All attempts to separate the quarks from a hadron have so far failed. It seems very easy to see. Today we have much better particle accelerators than in the past, where the particles collide with each other with a lot of energy to study the smaller particles that separate from them. It was in these particle accelerators that we discovered the Higgs boson, which further enhanced our standard model of particle physics. But despite all this modernity, we have never been able to separate a quark from a proton or a neutron into our study.

why like this? The secret of nature behind this that we have come to understand so far is that the color charge of the quarks binds the quarks in any hadron (proton or neutron) so tightly that no matter how hard we try to date As a result of separating quarks from other quarks, we get more pairs of quarks instead of one separate quark. This is a very interesting phenomenon. How does this happen? Let us explain this phenomenon a little.

Suppose we have a neutron which consists of one up quark and two down quarks. We want to get a quark out of this neutron. We have to give a lot of energy from outside for this. One way is to constantly throw high energy photons at this neutron or collide a high energy particle with it so that the configuration of the neutron is broken and we get the quarks in it separately. But one thing we have to keep in mind here is that the force between the quarks inside the neutron is the one that holds them tightly together. This is no small force. This is the strongest force in the universe which we call strong nuclear force so we have to give enough external energy here to overcome this force and we can separate the quarks inside the neutron.

What happens now is that as we increase the external energy, there comes a time when the quarks do not separate but the energy we provide is used to make a mass of two more quarks and instead of separating the quarks. Here we find a pair of quarks and an anti-quark. And that’s Einstein’s work.

Mass-Energy Equivalence Principle

Occurs under That is, the energy we used to separate the quarks


This mass is made up of two newly formed quarks.

As we took the example of the neutron above which consisted of one up quark and two down quarks and the energy we provided.


Paired Now these quarks will also move among themselves. That isThrough an up quark (u) and anti up quark (ū).

The configuration of neutrons was something like this

But after the energy exchange we got a pair of up quark (u) and an anti up quark (ū). So we have a total of four quarks. That is, three quarks of neutrons already existed and two more quarks merged with this energy. One of the two new quarks formed will be an up quark of neutrons, one up quark and one down quark, then there will be two up quarks and one down quark to form a hadron Which headron is this? This is the proton.

Now one down quark was saved from neutrons and one of the two new quarks formed was anti-up quark. Together they will make a hadron. What is a hadron particle consisting of a down quark and an anti-up quark? This is called pi-meson or pion. Which we explained in the previous article. The whole process is illustrated in the accompanying picture.

In short, before energy exchange, we only had one neutron, and when we tried to separate one of those neutrons into a quark and provide a lot of energy from outside, that energy turned into mass. The quarks could not be separated, but our neutrons changed to protons and we got a pie mason. Quark’s stubborn stubbornness remained in place and we failed to get free quarks. Whenever we try to separate quarks, we eventually get more quarks. In particle physics, this behavior and characteristic of quarks is called “quark confinement”, which is our inability to isolate a kind of quarks.

To sum up, some of the important things we have done are that we do not find quarks in a free state like other particles, mainly due to the strong force created by the color charge of quarks which They are very tightly bound inside a hadron particle. It seems that if we give energy to the quarks in a hadron particle, they can be free from that hadron, but quantum chromodynamics does not make it so easy. If we try to separate the quarks by breaking down protons or neutrons, we get more protons, neutrons or other mason particles.

Here, the unique attitude of the Strong Nuclear Force towards other forces is not without interest. During electromagnetic interaction, the electromagnetic force between two charged particles, such as two electrons, weakens, but the case with the strong nuclear force is somewhat different. Here, when the quarks are separated from each other, the strong force between them becomes stronger, while as the quarks get closer to each other, this force decreases. The reason is that the gluons have a color charge of their own and there can be 9 possible combinations of color charges on these gluons which are formed from the same three basic colors red, blue and green. (This can be explained in great detail through Feynman diagrams but the article will be very long). One way to understand this is that when one quark is far from the other, the gluons appear in greater numbers and their exchange is higher, which increases the force between the quarks, as opposed to when the quarks are close to each other. If so, the interchangeable gluons appear in small numbers, which also reduces the force between them. So as we move one quark away from the other. So we have to expend more energy to overcome this growing force between them, which eventually exceeds the energy required for pair production, and here the same energy is used instead of quark separation. Become more quarks. In quantum chromodynamics, the strengthening of the color force by increasing the distance between quarks is called asymptotic freedom, and this discovery was awarded the 2004 Nobel Prize to three physicists, David Grass, Frank Wilcheck, and David Politzar.

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