Nucleon - Quark Model Classification

Quark Model Classification

In the quark model with SU(2) flavour, the two nucleons are part of the ground state doublet. The proton has quark content of uud, and the neutron, udd. In SU(3) flavour, they are part of the ground state octet (8) of spin 1⁄₂ baryons, known as the Eightfold way. The other members of this octet are the hyperons strange isotriplet Σ+, Σ0, Σ−, the Λ and the strange isodoublet Ξ0, Ξ−. One can extend this multiplet in SU(4) flavour (with the inclusion of the charm quark) to the ground state 20-plet, or to SU(6) flavour (with the inclusion of the top and bottom quarks) to the ground state 56-plet.

The article on isospin provides an explicit expression for the nucleon wave functions in terms of the quark flavour eigenstates.