Dibaryon with Highest Charm Number near Unitarity from Lattice QCD

A pair of triply charmed baryons, ${\mathrm{\ensuremath{\Omega}}}_{ccc}{\mathrm{\ensuremath{\Omega}}}_{ccc}$, 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 ${\mathrm{\ensuremath{\Omega}}}_{ccc}{\mathrm{\ensuremath{\Omega}}}_{ccc}$ in the $^{1}{S}_{0}$ channel, taking into account the Coulomb repulsion with the charge form factor of ${\mathrm{\ensuremath{\Omega}}}_{ccc}$, leads to the scattering length ${a}_{0}^{\mathrm{C}}\ensuremath{\simeq}\ensuremath{-}19\text{ }\text{ }\mathrm{fm}$ and the effective range ${r}_{\mathrm{eff}}^{\mathrm{C}}\ensuremath{\simeq}0.45\text{ }\text{ }\mathrm{fm}$. The ratio ${r}_{\mathrm{eff}}^{\mathrm{C}}/{a}_{0}^{\mathrm{C}}\ensuremath{\simeq}\ensuremath{-}0.024$, whose magnitude is considerably smaller than that of the dineutron ($\ensuremath{-}0.149$), indicates that ${\mathrm{\ensuremath{\Omega}}}_{ccc}{\mathrm{\ensuremath{\Omega}}}_{ccc}$ is located in the unitary regime.