We explain what quarks are, how they were discovered and what the quark model is. Also, other subatomic particles.

Quarks are particles smaller than neutrons and protons.

What are quarks?

The quarks or quarks are a type of subatomic particle elemental, which falls within the category of fermions, and whose strong interactions constitute the matter of atomic nuclei. Its name comes from the novel Finnegan’s Wake by Irish author James Joyce.

The quarks are the particles of which protons Y neutrons they are made, as well as other types of tiny particles called hadrons.

These terms can be confusing, but you don't have to understand them at such technical levels to know what a quark is: the tiniest particles in the quark. matter, which interact freely with the four elemental physical forces: Gravitational force, electromagnetic force, strong nuclear force and weak nuclear force.

Along with leptons, quarks are the very building blocks of matter. Just as there is matter and antimatter, there are also quarks and antiquarks.

In addition, there are six types or "flavors" of quark. Thus, all the mesons and baryons of matter, that is, more than 200 different subatomic particles, can be built by combining three different quarks (or antiquarks) (baryons), or a quark-antiquark (mesons), united by strong interactions. .

Discovery of quarks

For many decades it was assumed that protons, neutrons, and electrons they were the fundamental particles of matter, that is, nothing could exist smaller than them.

However, the study of the so-called nucleons (neutrons and protons, inhabitants of the nucleus of the atom) showed that their size was much greater than that of electrons and that it could be assumed that they would in turn be made up of something smaller and simpler. The quarks came to answer that question.

Simultaneously, they were proposed in 1964 by Murray Gell-Mann and George Zweig, although completely independently. These scientists observed the need for quarks to exist by the nature of the strong interaction between particles in the atomic nucleus.

Furthermore, many of its properties were inexplicable unless there was structures internal inside protons and neutrons. Thus, the existence of three smaller particles, calledquorks (subsequentlyquarks, although Zweig initially proposed the nameaces or "aces"), which would have aelectric charge 1/3 and 2/3 load.

This hypothesis was tested experimentally in SLAC (Stanford Linear Accelerator Center or "Stanford Center for Linear Accelerator" in later years. But the experiment pointed out that there were not three but six particles that could make up protons and neutrons. For this discovery, Taylor, Kendall and Friedman won the 1990 Nobel Prize in Physics.

Quark model

Each type of quark has specific characteristics.

Within the standard model of matter that we handle today, quarks occupy the simplest place in matter.

Depending on the type of quarks that we combine, we can obtain different types of particles, according to the hadron classification rule (the so-called “quark model”), which establishes six different types of quark (or flavors, "Flavors"), each one endowed with a "quantum number" that defines its electrical charge:

  • Above (up). Endowed with an isospin +1/2 as a quantum number.
  • Below (down). Endowed with an isospin -1/2 as a quantum number.
  • Charm (charm). Endowed with a charm +1 as a quantum number.
  • Strange (strange). Endowed with a strangeness -1 as a quantum number.
  • Stop (top) or truth (truth). Endowed with a superiority (topness) +1.
  • Bottom (bottom) or beauty (beauty). Endowed with an inferiority (bottomness) -1.

All of this may look very strange and seem like something out of a video game, but it makes sense within the quark model, if we think that these tiny particles come together in triplets or triads to form different types of larger subatomic particles.

When the sum of their charges gives whole numbers, they form hadrons.

To this should be added, however, that quarks can have three more types of charge, which is the “color”. It is not really about the color, however, but that is the name that the scientists gave to this property which is a type of affinity, responsible for the strong nuclear attraction (through another particle called “gluons”).

These colors can be blue, green or red, and it is what distinguishes, for example, neutrons and protons from electrons (lepton-type particles), since the latter are not made of quarks and do not feel the strong nuclear interaction but the weak.

According to this model, the fundamental particles of matter are quarks and leptons.

Other subatomic particles

Other types of subatomic particles are:

  • Fermions. Together with bosons, they are the fundamental particles of matter, characterized by having a semi-integer spin or angular momentum (1/2, 3/2, etc.). There are only two types of fermions: quarks and leptons.
  • Leptons They are a type of fermion, endowed with ½ spin (either + or -) and that does not experience, unlike quarks, the strong nuclear interaction of matter. There are six types of leptons: electrons, muons, taus, electron neutrinos, muon neutrinos, and tau neutrinos. The first three have a +1 or -1 electric charge, and the rest have a 0 charge.
  • Bosons. Together with fermions, they are the fundamental particles of matter, characterized by having an integer spin (0, 1, 2, etc.) and do not comply with the Pauli exclusion principle. Examples of bosons are photons, gluons or gravitons, that is, particles that involve known forces.
  • Mesons. They are bosons, that is, hadrons of integer spin 0 or 1, which respond to the strong nuclear interaction, so they are made of quarks, according to the quark-antiquark state.
  • Baryons They are composed of three quarks and their most representative examples are the neutron and the proton, although there are also other types, extremely unstable.
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