Diquark Study in Quark Model

To investigate diquark correlation in baryons, the baryon spectra with different light–heavy quark combinations are calculated using Gaussian expansion method within both the naive quark model and the chiral quark model. By computing the diquark energies and separations between any two quarks in baryons, we analyze the diquark effect in the ud-q/Q, us-Q, ss-q/Q, and QQ-q/Q systems (where q=u,d, or s; Q=c,b). The results show that diquark correlations exist in baryons. In particular, for qq-Q and QQ-q systems, the same type of diquark exhibits nearly identical energy and size across different baryons. In the orbital ground states of baryons, scalar–isoscalar diquarks have lower energy and a smaller size compared to vector–isovector diquark, which qualifies them as “good diquarks”. In QQ-q systems, a larger mass of Q leads to a smaller diquark separation and a more pronounced diquark effect. In qq-Q systems, the separation between the two light quarks remains larger than that between a light and a heavy quark, indicating that the internal structure of such diquarks must be taken into account. A comparison between the naive quark model and the chiral quark model reveals that the introduction of meson exchange slightly increases the diquark size in most systems.