Diquark correlations in the nucleon Original Research Article

We investigate the structure of the nucleon and the Δ resonance employing a constituent chiral quark model. We propose a variational approach which allows the nucleon to have a [21] flavor-spin symmetry as well as the usual [3] symmetry. This means one gives also up the requirement that the spatial wave function must be symmetric [3]. One then has also to admix the [21] spatial symmetry for a total antisymmetrization and thus one allows quark-diquark correlations, where two quarks are more closely bound than the other two possible pairs. It is found that a quark pair with isospin T = 0 and spin S = 0 in the nucleon becomes spatially very close compared with other pairs in order to gain a strong attraction due to the pion exchange in the chiral quark model, which implies a diquark correlation in the nucleon. We also calculate the proton and neutron charge square radii.