We explain what quarks are, how they were discovered and what the quark model is. Also, other subatomic particles.
What are quarks?
Quarks or quarks are a type of elementary subatomic particle which falls within the category of fermionsand whose strong interactions constitute the matter of atomic nuclei. Its name comes from the novel Finnegan's Wake by the Irish author James Joyce.
Quarks are particles of which protons and neutrons are made as well as other types of tiny particles called hadrons.
These terms can be confusing, but it is not necessary to understand them at such technical levels to know what a quark is: the smallest particles of matter, which interact freely with the four elementary 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.
Additionally, 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 constructed by combining three different quarks (or antiquarks) (baryons), or a quark-antiquark (mesons), linked by strong interactions.
Discovery of quarks
For many decades it was assumed that protons, neutrons and electrons were the fundamental particles of matter, that is, that 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 larger than that of electrons and that this could mean that they would in turn be made up of something smaller and simpler. Quarks came to answer this 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 due to the nature of the strong interaction between particles of the atomic nucleus.
Furthermore, many of its properties were inexplicable unless there were internal structures within protons and neutrons. Thus, the existence of three smaller particles, called quorks (subsequently quarksalthough Zweig initially proposed the name aces or “aces”), which would have an electrical charge of 1/3 and 2/3 charge.
This hypothesis was experimentally verified in SLAC (Stanford Linear Accelerator Center or “Stanford Linear Accelerator Center) in later years. But the experiment indicated that there were not three but six particles that could make up protons and neutrons. For this discovery, Taylor, Kendall and Friedman won the Nobel Prize in Physics in 1990.
Quark model
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 various types of particles, according to the hadron classification rule (the so-called “Quark Model”), which establishes six different types of quark (either flavors“flavors”), each one endowed with a “quantum number” that defines its electrical charge:
- Above (up) Equipped with an isospin +1/2 as a quantum number.
- Below (down) Equipped with an isospin -1/2 as a quantum number.
- Charm (charm) Endowed with a +1 charm 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.
- Background (bottom) or beauty (beauty) Endowed with an inferiority (bottomness) -1.
All 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 we should add, however, that the 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 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 this 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 one.
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 spin ½ (either + or -) and that do 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 an electrical charge of +1 or -1, and the rest have a charge of 0.
- 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 entail known forces.
- Inns They are bosons, that is, hadrons with 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, highly unstable types.
Continue with: Quantum mechanics
References
- “Quark” on Wikipedia.
- “Quark model” on Wikipedia.
- “The quarks” in Astrojem.
- “Quarks” in Hyperphysics. (Spanish)
- “The quark revolution” in El País. (Spain)
- “Fifty years of quarks” at CERN.
- “What are quarks?” (video) at Fuse School.
- “Quark (subatomic particle)” in The Encyclopaedia Britannica.
