Quarks are particles smaller than protons and neutrons. They are the most fundamental elements of visible matter and that together form protons and neutrons.

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Quarks are the most fundamental particles of visible matter and that together form protons and neutrons. Quarks were discovered in the 1960’s

Quarks were discovered in the 1960’s

Quarks, along with electrons and neutrinos, are the smallest particles that man has managed to identify.

The theoretical analysis of the inelastic collisions caused in the linear accelerator in the SLAC, suggested several hypotheses to explain the shape function of the dispersion resulting from the collisions.

quarks SLAC
Stanford’s SLAC linear accelerator. Credit: web ssrl.slac.stanford.edu/pep-x/

One of these hypotheses was to consider that a proton is composed of positively charged point particles with spin 1/2.

With very conscientious studies it was found that such a hypothesis was adequate. This discovery earned Taylor, Kendall, and Friedmann, leaders of the experiments at SLAC, the 1990 Nobel Prize in Physics.

The word “quark” was coined in 1963 by the American physicist Murray Gell-Mann (1929) as a nonsense word that rhymed with Mark.

quarks Murray
Murray Gel-Mann Nobel Prize in Physics. Credit: web bbc.com/mundo/

Murray found the word “quark” in a book by James Joyce, in the phrase “Three quarks for Muster Mark”, which could be “Three quarters for Mister Mark.”

The number three fitted perfectly with what had been found inside protons and neutrons.

In those years only three types of quarks were known, and they were always in groups of three, in nucleons: protons and neutrons.

It has never been possible to isolate a quark. Solitary life is forbidden to them. They are always united in groups of three.

This ability to unite is due to the fact that they experience the action of the strong nuclear force. The work started by Murray to study this phenomenon is called Quantum Chromodynamics (CDC).

Currently, six types of quarks are known that particle physicists have named arbitrarily, but easy to remember and use:

  • Quark up (above) or simply u has electrical charge + ⅔
  • Quark down or just d has an electrical charge -⅓
  • Quark charm (enchanted) or simply c has an electric charge + ⅔
  • Quark strange (strange) or simply s has an electric charge -⅓
  • Quark top (top) or simply t has electrical charge + ⅔
  • Quark bottom (bottom) or simply b has electrical charge -⅓

The up and down varieties currently exist in nature in a stable way, and are distinguished between them by their electrical charge (among other characteristics).

The varieties s, c, b, and t are very unstable. Therefore, after the Big Bang, it took only a fraction of a second for them to disappear from the universe. Today, particle physicists can recreate and study them.

Protons and neutrons are made up of 3 quarks that combine to produce an entire charge.

The neutron consists of 3 quarks. Credit: CPAN website, i-cpan.es/es/content/

There is no information on fractional charges of isolated particles. It is currently unknown why the sum of the electric charges of the quarks in a proton corresponds exactly to that of an electron.

The quarks have spin + ½ or -½, so they are classified within the family of fermions.

The notion of the mass of a quark is a theoretical construction that makes sense only when you specify exactly what will be used to define it.

The mass of the quark can be measured directly from the resulting decay products in the Tevatron, which is the only particle accelerator with enough energy to produce abundant quarks.

The taste of a quark is related to the fact that quarks can change type, due to what is called the weak force.

The color of a quark has nothing to do with the perception of the frequency of light, but is related to quantum chromodynamics.

The quarks make up practically all the matter that we are surrounded by. Specifically, it is made up of up and down quarks, since they form protons and neutrons which, in turn, form atomic nuclei.

Rutherford’s atomic model established that the atom is not indivisible, but consists of a central nucleus with a positive electric charge and a cloud of electrons with a negative electric charge that revolve around it.

These three elementary particles (protons, neutrons and electrons) became four, when in the 1930s neutrinos appeared, indirectly.

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