Editing Color charge (section)

== History ==
Shortly after the existence of quarks was proposed by [[Murray Gell-Mann]] and [[George Zweig]] in 1964, color charge was implicitly introduced the same year by [[Oscar W. Greenberg]].<ref name=":0">{{Citation |last=Greenberg |first=Oscar Wallace |title=Color Charge Degree of Freedom in Particle Physics |date=2009 |work=Compendium of Quantum Physics |pages=109–111 |editor-last=Greenberger |editor-first=Daniel |url=https://link.springer.com/chapter/10.1007/978-3-540-70626-7_32 |access-date=2024-09-17 |place=Berlin, Heidelberg |publisher=Springer |language=en |doi=10.1007/978-3-540-70626-7_32 |isbn=978-3-540-70626-7 |editor2-last=Hentschel |editor2-first=Klaus |editor3-last=Weinert |editor3-first=Friedel}}</ref> In 1965, [[Moo-Young Han]] and [[Yoichiro Nambu]] explicitly introduced color as a gauge symmetry.<ref name=":0" />  

Han and Nambu initially designated this degree of freedom by the group [[SU(3)]], but it was referred to in later papers as "the three-triplet model". One feature of the model (which was originally preferred by Han and Nambu) was that it permitted integrally charged quarks, as well as the fractionally charged quarks initially proposed by Zweig and Gell-Mann.  

Somewhat later, in the early 1970s, Gell-Mann, in several conference talks, coined the name ''color'' to describe the internal degree of freedom of the three-triplet model, and advocated a new field theory, designated as ''quantum chromodynamics'' (QCD) to describe the interaction of quarks and gluons within hadrons. In Gell-Mann's QCD, each quark and gluon has fractional electric charge, and carries what came to be called ''color charge'' in the space of the color degree of freedom.