Is $d^{\ast }$ a candidate of hexaquark-dominated exotic state?

Abstract

We confirm our previous prediction of a $d^{\ast }$ 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 $d^{\ast }$ is a hexaquark dominated exotic state as it has about 2/3 hidden color (CC) configurations. By performing a more elaborate dynamical coupled-channels investigation of the $\Delta \Delta$-CC system within the framework of resonating group method (RGM) in a chiral quark model, we found that the $d^{\ast }$ 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 ensures that the $d^{\ast }$ has a rather narrow width which, together with the quantum numbers and our calculated mass, is consistent with the newly observed resonance-like structure ($M\approx 2380$ MeV, $\Gamma \approx 70$ MeV) in double-pionic fusion reactions reported by WASA-at-COSY Collaboration.

Comments: 4 pages, 2 figures