A model in which a baryon can be regarded as a bound state of two particles has been generalized to be approximately invariant under $\mathrm{SU}\left(6\right)\mathrm{}$. In the model, one of the constituent particles of a baryon can be regarded as a quark and the other particle can be considered as a tightly bound state of two quarks, or diquark. The quark is taken to belong to a six-dimensional representation of $\mathrm{SU}\left(6\right)\mathrm{}$, while the diquark is taken to belong to a twenty-one-dimensional representation. With this model, which can be considered as a specific dynamical approximation to the three-quark model, the baryon medium-strong mass splittings are calculated beyond lowest-order perturbation theory. The model provides a mechanism for breaking the Gell-Mann—Okubo baryon-octet mass formula while breaking the baryon-decuplet equal-spacing rule by a smaller amount.

• Received 16 October 1967

DOI:https://doi.org/10.1103/PhysRev.167.1535