Dibaryon with highest charm number near unitarity from lattice QCD

A pair of triply charmed baryons, ${\mathrm{\Omega }}_{ccc}{\mathrm{\Omega }}_{ccc}$, is studied as an ideal dibaryon system by (2+1)-flavor lattice QCD with nearly physical light-quark masses and the relativistic heavy quark action with the physical charm quark mass. The spatial baryon-baryon correlation is related to their scattering parameters on the basis of the HAL QCD method. The ${\mathrm{\Omega }}_{ccc}{\mathrm{\Omega }}_{ccc}$ in the ${}^1{S}_0$ channel taking into account the Coulomb repulsion with the charge form factor of ${\mathrm{\Omega }}_{ccc}$ leads to the scattering length $a_0^{\mathrm{C}}\simeq -19\text{ fm}$ and the effective range $r_{\mathrm{e}\mathrm{f}\mathrm{f}}^{\mathrm{C}}\simeq 0.45\text{ fm}$. The ratio $r^{\rm C}_{$\mathrm{e}\mathrm{f}\mathrm{f}$}/a^{\rm C}_0 \simeq -0.024$, whose magnitude is considerably smaller than that of the dineutron ($-0.149$), indicates that ${\mathrm{\Omega }}_{ccc}{\mathrm{\Omega }}_{ccc}$ is located in the unitary regime.