 Light-diquark spin-isospin correlation

Two light quarks in a symmetric spatial state and the antisymmetric colour pair inside a three-quark colour singlet require symmetric spin-flavour symmetry. Their isospin singlet and spin singlet are both antisymmetric, while their respective triplets are symmetric. Thus the allowed pairs have $(I,S_{ud})=(0,0)$ or $(1,1)$; opposite exchange parities are excluded. Coupling an isospin-zero spin-one-half quark gives an $I=0,J=1/2$ baryon or $I=1,J=1/2,3/2$ baryons.