Quark

Quark, particle believed by physicists to be the basic subunit of neutrons and protons. The quark theory was first proposed by 2 American physicists, Murray Gell-Mann and George Zweig in 1964. The theory holds that neutrons and protons consist of even simpler particles called quarks. Scientific studies have indicated evidence of quarks since 1971.

See also: Gluon; Hadron.