Is d^* a candidate for a hexaquark-dominated exotic state

We confirm our previous prediction of a d^* state with I(J^P) = 0(3⁺) [Phys. Rev. C 60, 045203 (1999)] and report for the first time based on a microscopic calculation that d^* has about 2/3 hidden color (CC) configurations and thus is a hexaquark-dominated exotic state. By performing a more elaborate dynamical coupled-channels investigation of the ΔΔ-CC system within the framework of the resonating group method (RGM) in a chiral quark model, we find that the d^* state has a mass of about 2.38-2.42 GeV, a root-mean-square radius (RMS) of 0.76-0.88 fm, and a CC fraction of 66%-68%. The last may cause a rather narrow width for the d^* which, together with the quantum numbers and our calculated mass, is consistent with the newly observed resonance-like structure (M ≈ 2380 MeV, Γ ≈ 70 MeV) in double-pionic fusion reactions reported by the WASA-at-COSY Collaboration. (authors)