Do you ask enough questions or do you settle for what you know? Of course, we humans didn’t settle for what we knew, we kept on asking different questions throughout history and one of the very important questions we tried answering is What is the universe made of or What are we made of? We got very interesting answers that we are made of matter, the matter that was formed in the early universe, but is that it? What can be more fundamental in the universe? The matter that makes all the stuff in the world is made up of Atoms. Atoms are made of Electron, Proton, Neutrons. These are the three major particles in an Atom. Electron is a fundamental elementary particle that cannot be divided into more fundamental particles. It is a point mass particle that cannot be broken down but Protons and Neutrons are not fundamental particles they can be divided into smaller particles. These particles which make Protons and Neutrons are QUARKS.
Quarks are the very fundamental particles that lie inside the Protons and Neutrons. There are many families of the elementary particles but these quarks make up the family called Hadrons in which Protons and Neutrons are part of it. Hadrons are particles that experience strong force interaction, which means they interact via the strong force. Hadrons are made up of quarks, different combinations of quarks form different types of Hadrons. To understand Pentaquarks and Tetraquarks first we must understand some properties of Quarks and these properties of quarks then will lead to understanding the formation of Pentaquarks and Tetraquarks. Firstly, the Hadrons are further classified into two groups Baryons and Mesons. Baryons are made of three colour quarks and Mesons are made of one quark and one antiquark pair. There are three primary Quarks: Up, Down, Strange, and their Anti –particles.
These are called the flavour of Quarks. Neutrons are made up of Two Down quarks and one Up quark and Proton is made up of two Up quarks and one Down quark. All these different combinational of quarks form the different types of Hadron Particles.
All these quarks have the charges associated with them and the sum of those charges defines the charge properties of hadrons, for example, take a Neutron, it is a neutral particle so the sum of the charges of the quarks comes zero in teams of Neutron so neutron is neutral. If we take another example of Proton, the Proton is a positively charged particle and so the sum of the charges of quarks comes out to be 1. Therefore, the Proton is a positively charged particle. These properties of quarks can explain the formation of different types of Hadrons particles. But there is a problem with these quarks that are arranged in Hadrons like in Neutron, there are three quarks two Down and one Up quark so these two Down quarks are similar and just like Neurons there are many Hadrons Particles which have these similar quarks in their arrangement. And these quarks are Spin ½ particles. If you know the Exclusion Principle for particles having ½ integer spin no more than one similar particle can exist in the same Quantum state. So, if this is true then how can these similar quarks can be in the same state. Here the color Property of Quarks comes in the picture. To explain the Exclusion principle, this Colour property of quarks was introduced. So, these quarks are assigned six different color properties that are RED, GREEN, BLUE and ANTI-RED, ANTI-BLUE, ANTI-GREEN for the anti-quarks. here there is nothing to do with color it's just how their properties are represented or it is just a naming convention and this color represent some kind of quantum property and this different types of colors can help us to understand the properties of quarks. Hadrons are colorless if you understand the analogy, the idea behind it is that the arrangement of quarks in Hadrons are in such a way that all these three quarks come together to make a WHITE color and all Hadron particles are colorless in nature. If you take an example of meson particle it has RED and Anti-RED quark and if we look at the combination of these two colors will give us a WHITE color or a colorless particle. Another example is if you take three Quarks RED, GREEN, BLUE they end up creating a WHITE color or the colorless particle.
Only Quarks can wield this property in nature and Hadrons which are not colorless cannot exist in nature means the hadron with two quarks with RED and BLUE cannot exist because the combination of these two colors is not colorless. Therefore, due to this property of quarks, we can define the properties of Hadron particles.
The second property of quarks is QUARKS FLAVOUR. yes the flavour!! Up till now, we have seen three types of quarks UP, DOWN, STRANGE Quark but there are more quarks are found in nature. Today at this point we have discovered six quarks the three more additional quarks are CHARM Quark, TOP Quark, and BOTTOM Quark.
All these types of Quarks are said to be or named to be FLAVOUR of Quarks. Now if you have understood all the main Properties of quarks let's move to the title of this article, Penta-Quarks, and Tetra-Quarks. On 21st August, LHCB Experiment at CERN discovers several exotic particles of four Quarks rather say a combination of TWO Quarks and TWO Anti –Quarks which was named TETRA-QUARKS. These are four heavy Quarks made up of two CHARM QUARKS and two ANTI-CHARM QUARKS. Whereas this CHARM Quarks are one of the flavours of Quarks that we have seen, now can this four Quarks combination exist in nature as we know we have three combinations of Quarks which we called Baryons and combination of two Quarks we call as Meson so can it is possible? Now if we come to TETRA-Quarks consider the color property of a Quark, the TWO CHARM-Quark, and TWO ANTI-CHARM Quark let's consider the TWO CHARM Quark has a color property of RED and BLUE and another TWO ANTI-CHARM Quark has a color property of ANTI –RED, and ANTI –BLUE so you the combination of this four colors are WHITE and All Hadrons are colorless in Nature so this combination of four Quarks are possible in nature which means this four Quarks or TETRA-Quarks can exist in Nature isn't it intriguing !!
So this combination of RED, BLUE, GREEN, ANTI-RED, ANTI-BLUE, ANTI-GREEN gives us a WHITE color which we need to make a Hadron particle colorless if these four combinations of Quarks are possible then why not FIVE Quarks combination that is PENTA-QUARKS. In 2019, the LHCB experiment confirmed that PETA- QUARKS exist in Nature and why not if we take five different color combinations of Quarks which can give us WHITE color then as we know the Hadrons are colorless then this satisfies our color property of Quarks. PENTA-QUARKS and TETRA – QUARKS are the most exotic particles in nature and this discovery is helping the scientist to study strong interaction in more depth and it is possible that we can find more exotic particles which are different but has similar property like PENTA and TETRA Quarks. What more we can find, what more can we discover in an infinite universe, anything that could be imagined might somewhere EXIST !!!