astronomyblog:

What are Quarks?

A quark is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei.

There are six types of quarks, known as flavors: up, down, strange, charm, top, and bottom Up and down quarks have the lowest masses of all quarks. The heavier quarks rapidly change into up and down quarks through a process of particle decay: the transformation from a higher mass state to a lower mass state. Because of this, up and down quarks are generally stable and the most common in the universe, whereas strange, charm, bottom, and top quarks can only be produced in high energy collisions (such as those involving cosmic rays and in particle accelerators).

Due to a phenomenon known as color confinement, quarks are never directly observed or found in isolation; they can be found only within hadrons, such as baryons (of which protons and neutrons are examples) and mesons. For this reason, much of what is known about quarks has been drawn from observations of the hadrons themselves. 

This movie illustrates the action inside the nucleus of a deuterium atom containing a proton and a neutron, each with three quarks. An electron strikes a quark inside a proton, passing energy to the quark before the electron bounces back. The quark now has so much energy “stuffed” into it, it creates a cascade of new particles as it flies out of the proton. The result is two new, two-quark particles.

Quarks have various intrinsic properties, including electric charge, mass, color charge, and spin. Quarks are the only elementary particles in the Standard Model of particle physics to experience all four fundamental interactions, also known as fundamental forces (electromagnetism, gravitation, strong interaction, and weak interaction), as well as the only known particles whose electric charges are not integer multiples of the elementary charge.

An animation of the interaction inside a neutron. The gluons are represented as circles with the color charge in the center and the anti-color charge on the outside. 

• Mass 

Current quark masses for all six flavors in comparison, as balls of proportional volumes. Proton and electron (red) are shown in bottom left corner for scale.

Two terms are used in referring to a quark’s mass: current quark mass refers to the mass of a quark by itself, while constituent quark massrefers to the current quark mass plus the mass of the gluon particle field surrounding the quark. These masses typically have very different values. Most of a hadron’s mass comes from the gluons that bind the constituent quarks together, rather than from the quarks themselves. 

• Field lines from color charges 

In quantum chromodynamics, a quark’s color can take one of three values or charges, red, green, and blue. An antiquark can take one of three anticolors, called antired, antigreen, and antiblue (represented as cyan, magenta and yellow, respectively). Gluons are mixtures of two colors, such as red and antigreen, which constitutes their color charge. QCD considers eight gluons of the possible nine color–anticolor combinations to be unique.

• Spin

In quantum mechanics and particle physics, spin is an intrinsic form of angular momentum carried by elementary particles, composite particles (hadrons), and atomic nuclei.

Spin is one of two types of angular momentum in quantum mechanics, the other being orbital angular momentum. The orbital angular momentum operator is the quantum-mechanical counterpart to the classical angular momentum of orbital revolution: it arises when a particle executes a rotating or twisting trajectory (such as when an electron orbits a nucleus)

• Gluon

A gluon is an elementary particle that acts as the exchange particle (or gauge boson) for the strong force between quarks. It is analogous to the exchange of photons in the electromagnetic force between two charged particles. In layman’s terms, they “glue” quarks together, forming protons and neutrons.

• Baryons and Mesons

A baryon is a composite subatomic particle made up of three quarks. Baryons and mesons belong to the hadron family of particles, which are the quark-based particles. 

As quark-based particles, baryons participate in the strong interaction, whereas leptons, which are not quark-based, do not.

In particle physics, mesons are hadronic subatomic particles composed of one quark and one antiquark, bound together by the strong interaction. Because mesons are composed of quark sub-particles, they have a physical size, with a diameter of roughly one femtometer, which is about  ²⁄₃ the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond. Charged mesons decay (sometimes through mediating particles) to form electronsand neutrinos. Uncharged mesons may decay to photons. Both of these decays imply that color is no longer a property of the byproducts.

• Source: wikipedia, hyperphysics
• (To know more click the links: Baryon, Meson, Gluon)
•  Images: x, x, x, x, x