Nobel prize to M. Gell-Mann awarded in 1969 "for his contributions and discoveries concerning the classification of elementary particles and their reactions''
Gell-Mann, M.; Isotopic Spin and New Unstable Particles
Phys. Rev. 92 (1953) 833;
Reprinted in The Physical Review - the First Hundred Years, AIP Press (1995) CD-ROM.
In connection with the work of Peaslee and of Pais, the author would like to put forward an alternative hypothesis that he has considered for some time, and which, like that of Pais, overcomes the difficulty posed by electromagnetic interactions. Let us suppose that the new unstable particles are fermions with integral isotopic spin and bosons with half-integral isotopic spin. For example, the V1 particles may form an isotopic triplet, consisting of V1+, V10,
and V1-. The + and V40 may form an isotopic doublet, which we may call + and 0. (Extracted from the introductory part of the paper.).
Related references See also A. Pais, Phys. Rev. 86 (1952) 663;
D. C. Peaslee, Phys. Rev. 86 (1952) 127;
Extension of isotopic multiplet structure for new unstable particles. Explanation of pairwise production of V particles.