The evidence of the charm quark in the proton structure surprised physicists!

The proton, the familiar particle to most people, is a combination of three lighter particles; Particles that are called quarks and in the case of protons include a combination of two up quarks and one down quark (intrinsic quarks). On the other hand, for decades, physicists have speculated that protons may host heavier quarks called charm quarks! Meanwhile, physicists reported on August 18 this year in the journal "Nature" that a new analysis supports this shocking idea.

BingMag.com The evidence of the charm quark in the proton structure surprised physicists!

The proton, the familiar particle to most people, is a combination of three lighter particles; Particles that are called quarks and in the case of protons include a combination of two up quarks and one down quark (intrinsic quarks). On the other hand, for decades, physicists have speculated that protons may host heavier quarks called charm quarks! Meanwhile, physicists reported on August 18 this year in the journal "Nature" that a new analysis supports this shocking idea.

What is the charm quark and what is strange about it?

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In the framework of the standard model, there are 6 types of quarks named top (u), bottom (d), enchantment (c), surprise (s), head (t) and bottom (b)! Meanwhile, "Charm Quark" is the third heaviest quark among these particles. In general, until today, physicists thought that the proton consists of a combination of two up quarks and one down quark, but the possibility of the charm quark in the structure of this particle made the story very different! Charm quarks are much heavier than up or down quarks, so much so that they can amazingly form a compound heavier than the proton itself! On the other hand, physicists in any branch know very well that the deeper they dig into anything, including the proton, the more complex the structures seem to understand. This issue is especially observed in very high energies and collisions in particle accelerators such as the Large Hadron Collider (LHC). Therefore, by going deeper and entering much smaller scales (despite higher energies), protons can be composed of It considered a complex (literally tangled) and unstable group of quarks along with their antimatter counterparts, the antimatter counterparts. It is interesting to know that in such a situation these particles are called gluons, which are divided into quark-antiquark pairs (extrinsic quarks) in the proton!

A gluon can be considered a particle that is exchanged between quarks to stick them together.

You may have thought to yourself until this point of the text, what finally happened! Is a proton made up of two up quarks and one down quark, or quark-antiquark pairs (also called outer quarks)? In response and in order to clarify the issue, you should know that the outer quarks are not fundamental particles in the structure of the proton, in fact these pairs of quarks and antiquarks are simply the result of the behavior (decay) of gluons at high energies. But at the same time, new studies show that in addition to up and down quarks, charm quarks may also exist inside protons even at low energies in a more stable and deeper way.

Besides the understanding that Physicists know about the quark structure of the proton, new studies show that in addition to the up and down quarks, there is also a stable and deep charm quark in the proton structure!

As you know in quantum physics, particles until which are not measured, do not have a specific state and are described only by probabilities. According to the same principle, physicists admit that if protons have charmed quarks in their structure, there is a small possibility for the presence of a pair of charmed quarks-antiquarks along with two up and one down quarks in the structure of these particles. Of course, since protons are not a collection of individual particles and their mass is not obtained from the simple sum of the mass of the particles inside it, the mass of the charm quark and its antiquark is not added to the weight of the proton; Therefore, we can have an understanding of how there are particles heavier than the proton inside the proton itself! They play an essential role in the formation of the nucleus structure of atoms. But it is interesting to know that after years of study, our understanding of this particle is still not complete and they can surprise us at any time! All atoms are composed of protons (red), neutrons (blue) and a cloud of electrons that surrounds it. The number of protons determines the type of element.

BingMag.com The evidence of the charm quark in the proton structure surprised physicists!

A deeper look (proton structure)

Protons are made of two up quarks and one down quark while neutrons are made of two down quarks and one up quark!

BingMag.com The evidence of the charm quark in the proton structure surprised physicists!

A deeper look than deep

Protons and neutrons are more than The structures are simple, and quark-antiquark pairs are constantly created and annihilated around their three stable quarks! Gluons (yellow) hold quarks together through the strong nuclear force. On the other hand, it is interesting to know that quarks have a property called "color charge" (in shown here in red, green, and blue) that depend on the strong nuclear force.

BingMag.com The evidence of the charm quark in the proton structure surprised physicists!

How to prove the existence of a bunch of particles in the heart of other particles?

In this regard, physicists using thousands of different measurements in the LHC laboratory and other particle accelerators along with theoretical calculations came to the conclusion that the charm quark inside the proton With an uncertainty of 3 sigma, it is also reported that charm quarks carry about 0.6% of the proton's momentum. However, you should keep in mind that usually obtaining a 5-sigma uncertainty is required to provide a definitive result. And so far this value has not been seen in uncertainty!

In order to better understand the statistical analysis presented in this section, it is better to know that since in the world of particle physics, various processes are inherently probabilistic and On the other hand, we can only look at a finite number of data, it is natural to deviate from the ideal value. In the world of science and statistics, this deviation is represented by the Greek letter sigma, and it indicates the probability of obtaining a real result.

Generally, the larger sigma is equal to the more improbable results that will surprise us. Was! Because if you flip a fair coin 100 times, our expectation is that the probability of tails or lines is about 50%, and if you get lines between 45 and 55 cases, we can conclude that the deviation is about 1 sigma, which is not so strange! But if you get a line in 75 throws, we will realize that the coin is not fair and probably an unseen hand is involved in this matter; In such a case, we will face the result of 5 sigma!

  • Artificial intelligence also challenged physicists!

The last word

Besides these evidences, it is necessary to emphasize that the data and analysis are still not enough to claim the existence of charm quarks in protons; Although the statistical value of 3 sigma is very significant! In addition, the definition of enchanted quarks is not very straightforward and it hinders the comparison of new findings with previous results of different groups. It means that during previous studies, different limits for charm quark have been presented according to its definition, which is not in agreement with the results! Therefore, scientists need to smash protons with more efforts to discover the secret of this familiar yet mysterious particle!

Main sources:

The NNPDF Collaboration. Evidence for intrinsic charm quarks in the proton. Nature. Vol. 608, August 18, 2022, p. 483. doi: 10.1038/s41586-022-04998-2.

LHCb Collaboration. Study of Z bosons produced in association with charm in the forward region. Physical Review Letters. Vol. 128, February 25, 2022, p. 082001. doi: 10.1103/PhysRevLett.128.082001.

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