  Ground-state energies are investigated in a many-quark model with pairing
interactions, which has the su(4)-algebraic structure. Exact eigenstates in the
boson realization method are constructed by imposing a color-singlet condition
developed in the previous paper. An interaction term breaking the
su(4)-dynamical symmetry plays an important role to determine the ground state.
As a result, a quark-pairing state or a quark-triplet state as a nucleon is
realized with a certain value of a variable which is regarded as an order
parameter. In addition to the parameter regions in which these ground states
are realized, it is shown that there are two transition regions between the
quark-pairing and the quark-triplet states with different values of the order
parameter.
