The Discovery of Colour
Colour quantum numbers have been used from the beginning. However, colour was discovered as a consequence of this classification when it was realized that the spin S = 3⁄2 baryon, the Δ++ required three up quarks with parallel spins and vanishing orbital angular momentum, and therefore could not have an antisymmetric wavefunction unless there was a hidden quantum number (due to the Pauli exclusion principle). Oscar Greenberg noted this problem in 1964, suggesting that quarks should be para-fermions. Six months later Moo-Young Han and Yoichiro Nambu suggested the existence of three triplets of quarks to solve this problem. The concept of colour was definitely established in the 1973 article written jointly by William Bardeen, Harald Fritzsch and Murray Gell-Mann.
Read more about this topic: Quark Model, Baryons
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