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Quark theory

Quark
Three colored balls (symbolizing quarks) connected pairwise by springs (symbolizing gluons), all inside a gray circle (symbolizing a proton). The colors of the balls are red, green, and blue, to parallel each quark's color charge. The red and blue balls are labeled "u" (for "up" quark) and the green one is labeled "d" (for "down" quark).
A proton is composed of two up quarks, one down quark, and the gluons that mediate the forces "binding" them together. The color assignment of individual quarks is arbitrary, but all three colors must be present.
Composition Elementary particle
Statistics Fermionic
Generation 1st, 2nd, 3rd
Interactions Electromagnetism, gravitation, strong, weak
Symbol
q
Antiparticle Antiquark (
q
)
Theorized
Discovered SLAC (c. 1968)
Types 6 (up, down, strange, charm, bottom, and top)
Electric charge +​2⁄3 e, −​1⁄3 e
Color charge Yes
Spin ​1⁄2
Baryon number ​1⁄3

A quark (/kwɔːrk, kwɑːrk/) 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. Due to a phenomenon known as color confinement, quarks are never directly observed or found in isolation; they can be found only within hadrons, which exist as either baryons (which include protons and neutrons) or as mesons. For this reason, much of what is known about quarks has been drawn from observations of hadrons.

Quarks have various intrinsic properties, including electric charge, mass, color charge, and spin. They 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.


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