The quark , together with leptons , are the smaller particles forming the ordinary matter , so are described as elementary particles .
Although they have not been observed directly, they have been observed through their interaction with other particles.
According to these observations, quarks have been cataloged in various types according to their “color” and “taste” , although the name of these properties is completely arbitrary and has nothing to do with what they actually represent.
Flavors and colors are quantum properties of quarks. The flavors could be understood as types of quarks , while the color is usually explained as a type of cargo, the ” color charge “.
Other intrinsic properties of quarks are electric charge, mass and spin.
Up to six different flavors have been observed , related to the weak interaction force, and 3 colors , related to the strength of strong interaction.
All these types of quarks would be provided in the mathematical formulation of the so-called standard model of particle physics.
In addition to the strong and weak interaction, quarks also experience gravitation and electromagnetism, so they are the only particles of the standard model that experience the four fundamental forces of interaction .
The taste of quarks
The flavor is the name with which they differentiate the modalities or species of a same type of particle . Each of them is parameterized by a quantum number and can be described by the horizontal symmetries between the quark-lepton generations.
There are six flavors of quarks:
- u (up)
- c (charm)
- t (top)
- d (down)
- s (strange)
- b (bottom)
Through experiments in particle accelerators , it has been possible to verify the existence of the six flavors of quarks, although as previously stated, they have never been observed directly, but different manifestations of their existence have been observed.
The quarks of the family up (up, charm and top) have a positive charge of 2/3, and the quarks of the family down (down, strange and bottom) have a negative charge of -1/3. In addition, each type of quark has a slightly different mass.
The combination of the load and the mass, together with other properties of the quarks, make up the different types, species or flavors of quarks.
For each type of quark there is an antiparticle, an antiquark (anti-up, anti-top, etc.), which has the same magnitude of its properties but of opposite sign.
The combination of different types of quarks gives rise to hadrons . Within the hadrons we have the mesons , formed by a quark and antiquark, and the baryons , formed by three quarks.
The protons and neutrons of the atomic nuclei are baryon type hadrons , since they are formed by the combination of three quarks:
- Protons : formed by two quarks up and one down (uud) . Positive elemental charge.
- Neutrons : formed by two quarks down and one up (udd) . Neutral elementary charge.
Taste and weak interaction strength
A quark of one flavor can be transformed into a quark of another flavor by the weak interaction, an interaction due to the exchange of W bosons .
When emitting or absorbing a W-boson, a quark of type up (up, charm, top) can be transformed into quark of type down (down, strange, bottom), and vice versa.
This change of flavor in quarks by weak interaction is the mechanism of decay or beta decay in which a neutron disintegrates into a proton, an electron and an electronic antineutrino .
Beta decay occurs when one of the neutron down quarks (udd) is transformed into an up quark, which gives rise to a proton (uud). In this flavor transformation, a W-boson is emitted, and this boson decays to an electron and an electronic antineutrino.
|n||?||p||+||e –||+||? e||(beta decay, hadron notation)|
|udd||?||uud||+||e –||+||? e||(beta decay, notation in quarks)|
The up and down quarks are the lightest quarks. Heavier quarks tend to be less stable and decay to states with less mass. Because of this, quarks up and down are the most abundant in the universe . The other flavors of quarks are only seen in high-energy collisions like those that occur in cosmic rays and in particle accelerators.
The color loading
Color, or color loading, is a property of quarks studied by quantum chromodynamics , although quarks do not have a color we can see.
The quarks that form a hadron, for example a proton, occupy a tiny space, and according to the Pauli exclusion principle , two particles in the same quantum state can not exist in the same space and at the same time.
That is, two quarks up could not be inside a single proton, nor two quarks down could be inside a neutron, but they are. For this to happen, those quarks of the same flavor have to have another quantum property that is different, and that property is known as color or color loading .
There are three possible colors: blue, red and green . Each of the six flavors of quarks can carry one of the three colors. For each color there is the same property of opposite sign, anticolor (anti-blue, anti-green and anti-red). Each quark carries a color, while an antiquark carries an anti-color.
Although it may seem a bit strange, the different experiments in particle accelerators have confirmed that there are 3 times more types of quarks than would be expected if only the taste were taken into account, which is usually taken as proof of the color load .
Color and strength of strong interaction
The system of attraction or repulsion between quarks with different colors , the field of study of quantum chromodynamics, is the representation of the strong interaction force . This interaction force is mediated by the absorption or emission of gluons .
A quark that carries a certain charge of color can form a system of union with an antiquark with the corresponding anticolor. The result of this interaction are the mesons . The color of the quark is neutralized with anti-quark anti-color, so mesons have no color (zero color charge).
Similarly, the combination of 3 quarks , each with a different color charge, results in the formation of baryons . The union of 3 anti-quarks, each with a different anticolor, gives rise to the anti-baryons.
Thus, each flavor of a quark, f (of the English flavor), exists in three states, f B , f G and f R , according to its color charge (Blue, Green or Red). This forms a quantum field of three components whose transformations follow the gauge symmetry called SU (3) , the basis of quantum chromodynamics that determines the properties of the strong interaction.
According to SU (3) symmetry there must be up to 8 types of gluons that act as carrier particles of the strong interaction between quarks.