One of these discovere simultaneously by two groups in 1974 was the first example of charmonium and provided evidence for the extension of their namesake octet based on the Eightfold Way.
The eight lightest ones are all pseudoscalars, while the heaviest one, discovered in 1977 by a group headed by Leon Lederman, is a vector. Another variety of these particles was involved in the tau-theta puzzle, which was resolved by noting that in certain particles of this type, charge-parity symmetry was violated. One of these discovere simultaneously by two groups in 1974 was the first example of charmonium and provided evidence for the extension of their namesake octet based on the Eightfold Way. First proposed by Hideki Yukawa and initially mistaken for the muon, for ten points, identify these hadronic spin-one particles which consist of quark-antiquark pairs and exaples of which are the pi and the j/psi.
The eight lightest ones are all pseudoscalars, while the heaviest one, discovered in 1977 by a group headed by Leon Lederman, is a vector.
{meson}