Quark

6 flavors of Quarks and their generations showing charge and spin

The name "quark" was taken by Murray Gell-Mann from the book "Finnegan's Wake" by James Joyce. The line "Three quarks for Muster Mark" appears in the fanciful book. Gell-Mann received the 1969 Nobel Prize for his work in classifying elementary particles. There are six adjectives used with quarks making three families, each family comprised of two quarks.

Quarks and Leptons are the building blocks which build up matter, i.e., they are seen as the "elementary particles". In the present standard model, there are six "flavors" of quarks. They can successfully account for all known mesons and baryons (over 200). The most familiar baryons are the proton and neutron, which are each constructed from up and down quarks. Quarks are observed to occur only in combinations of two quarks (mesons), three quarks (baryons). There was a recent claim of observation of particles with five quarks (pentaquark), but further experimentation has not borne it out .

According to physics, a substance can be divided into smaller pieces or atoms, which can be divided into a nucleus and electrons; and the nucleus into protons and neutrons. A proton or neutron consists of three quarks, which combine with each other by exchanging gluons. At present, quarks and gluons are considered to be types of elementary particles.

There are two types of Hadrons, the Baryon which is a system of three quarks (e.g. the proton) or Mesons, a two quark system containing a quark - antiquark pair (e.g. the pion or pi-meson). Baryons are usually confined within nuclei as are unstable and decay if isolated, for example a neutron has a lifetime of about fifteen minutes if not inside the nucleus. The exception to this is the proton which is essentially stable in free space .

Quark Fact Points

Image showing composition of a proton/neutron with all three colours

(i) A Quark is pronounced as Kwark. It is basically an elementary particle. It is one of the fundamental constituent of matter.

(ii) There are 6 types, or "flavors," of quarks: up (U), down (D), charm (C), strange (S), top (T) and bottom (B). These flavors of quarks combine to form all the known mesons and baryons.

(iii) Their names do not really mean anything, just that they are different kinds of quarks.

(iv) Hadrons are thought to be composed of quarks, with baryons having three quarks and mesons having a quark and an antiquark.

(v) Quarks bind together with gluons to make composite particles called Hadrons. Baryons and mesons belong to Hadrons.

(vi) Quarks come in six flavors and three colors and occur only in combinations that produce white.

(vii) Gluons are the quark binding particle.

(viii) They cannot exist independently. A quark exhibits confinement, which means that the quarks are not observed independently but always in combination with other quarks. This makes determining the properties (mass, spin, and parity).

(ix) The anti-particle of a quark is the antiquark. Quarks and antiquarks are the only two fundamental particles that interact through all four fundamental forces of physics.

(x) The flavour of the quark determines its properties. Quarks with a charge of +(2/3) are called up-type quarks and those with a charge of -(1/3) are called down-type.

Quark and Standard Model of Particle Physics

The Standard Model of particle physics has been extremely successful in describing the interactions and behaviors of subatomic particles, but many important puzzles remain. One mystery is the origin of the masses for particles called quarks, which make up protons and neutrons, and leptons, of which the best known is the electron. These masses vary widely; for example, the lightest quark, the "up" quark, is lighter than the heaviest quark, the "top" quark, by a factor of 100,000. The Standard Model does not explain the mass ratios between quarks and leptons. Leading theories of physics beyond the Standard Model, such as the popular theory of supersymmetry, also do not address this question . At present there is no evidence of any structure to the quark. Inspite of this fact Quarks are constituents of sub-atomic particles and as a result matter gets physical structure through atom and molecules.

Quarks and Leptons

The Standard Model of Particle Physics, which is strongly supported by extensive experimental results, suggests the material universe is assumed to be built by a small number of fundamental particles: Quarks & Electron-like particles called Leptons. Quarks bind together through the strong interaction to make, for example, protons and neutrons. Leptons do not take part in the strong interaction, and only interact via the electromagnetic and weak forces. Quarks, at least in normal circumstances, exist only in bound states. Leptons, on the other hand, can be individually observed.

Types of leptons: There is experimental evidence for six different kinds of leptons – three negatively electrically charged leptons, and three electrically neutral. The best known electrically charged leptons are:
(1) the electron (e)
(2) the muon (μ)
(3) the tauon (τ)

The three electrically neutral leptons are the neutrinos (ν). Associated to each charged lepton, there are three distinct kinds of neutrinos:

(1) the electron neutrino (νe)

(2) the muon neutrino (νμ)

(3) the tauon neutrino (νε)

For each of these leptons there is also an associated anti-particle, which has the same mass but opposite charge. The electron is familiar to everyone. It is directly tied to the chemical properties of almost all atoms. It is the smallest charged particle we know of and is very stable. The electron's antiparticle, the positron, is identical in mass but has a positive charge. It was the first particle of antimatter that was discovered .