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The $OmegaOmega$ system in the $^1S_0$ channel (the most strange dibaryon) is studied on the basis of the (2+1)-flavor lattice QCD simulations with a large volume (8.1 fm)$^3$ and nearly physical pion mass $m_{pi}simeq 146$ MeV at a lattice spacing $asimeq 0.0846$ fm. We show that lattice QCD data analysis by the HAL QCD method leads to the scattering length $a_0 = 4.6 (6)(^{+1.2}_{-0.5}) {rm fm}$, the effective range $r_{rm eff} = 1.27 (3)(^{+0.06}_{-0.03}) {rm fm}$ and the binding energy $B_{Omega Omega} = 1.6 (6) (^{+0.7}_{-0.6}) {rm MeV}$. These results indicate that the $OmegaOmega$ system has an overall attraction and is located near the unitary regime. Such a system can be best searched experimentally by the pair-momentum correlation in relativistic heavy-ion collisions.
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The $DeltaDelta$ dibaryon resonance $d^ast (2380)$ with $(J^P, I)=(3^+, 0)$ is studied theoretically on the basis of the 3-flavor lattice QCD simulation with heavy pion masses ($m_pi =679, 841$ and $1018$ MeV). By using the HAL QCD method, the central $Delta$-$Delta$ potential in the ${}^7S_3$ channel is obtained from the lattice data with the lattice spacing $asimeq 0.121$ fm and the lattice size $Lsimeq 3.87$ fm. The resultant potential shows a strong short-range attraction, so that a quasi-bound state corresponding to $d^ast (2380)$ is formed with the binding energy $25$-$40$ MeV below the $DeltaDelta$ threshold for the heavy pion masses. The tensor part of the transition potential from $DeltaDelta$ to $NN$ is also extracted to investigate the coupling strength between the $S$-wave $DeltaDelta$ system with $J^P=3^+$ and the $D$-wave $NN$ system. Although the transition potential is strong at short distances, the decay width of $d^ast (2380)$ to $NN$ in the $D$-wave is kinematically suppressed, which justifies our single-channel analysis at the range of the pion mass explored in this study.
The nucleon($N$)-Omega($Omega$) system in the S-wave and spin-2 channel ($^5$S$_2$) is studied from the (2+1)-flavor lattice QCD with nearly physical quark masses ($m_pi simeq 146$~MeV and $m_K simeq 525$~MeV). The time-dependent HAL QCD method is employed to convert the lattice QCD data of the two-baryon correlation function to the baryon-baryon potential and eventually to the scattering observables. The $NOmega$($^5$S$_2$) potential, obtained under the assumption that its couplings to the D-wave octet-baryon pairs are small, is found to be attractive in all distances and to produce a quasi-bound state near unitarity: In this channel, the scattering length, the effective range and the binding energy from QCD alone read $a_0= 5.30(0.44)(^{+0.16}_{-0.01})$~fm, $r_{rm eff} = 1.26(0.01)(^{+0.02}_{-0.01})$~fm, $B = 1.54(0.30)(^{+0.04}_{-0.10})$~MeV, respectively. Including the extra Coulomb attraction, the binding energy of $pOmega^-$($^5$S$_2$) becomes $B_{pOmega^-} = 2.46(0.34)(^{+0.04}_{-0.11})$~MeV. Such a spin-2 $pOmega^-$ state could be searched through two-particle correlations in $p$-$p$, $p$-nucleus and nucleus-nucleus collisions.
A pair of triply charmed baryons, $Omega_{ccc}Omega_{ccc}$, 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 $Omega_{ccc}Omega_{ccc}$ in the ${^1S_0}$ channel taking into account the Coulomb repulsion with the charge form factor of $Omega_{ccc}$ leads to the scattering length $a^{rm C}_0simeq -19~text{fm}$ and the effective range $r^{rm C}_{mathrm{eff}}simeq 0.45~text{fm}$. The ratio $r^{rm C}_{mathrm{eff}}/a^{rm C}_0 simeq -0.024$, whose magnitude is considerably smaller than that of the dineutron ($-0.149$), indicates that $Omega_{ccc}Omega_{ccc}$ is located in the unitary regime.
We present the energy spectra of the low lying doubly-charmed baryons using lattice quantum chromodynamics. We precisely predict the ground state mass of the charmed-strange Omega(cc) (1/2+) baryon to be 3712(11)(12) MeV which could well be the next doubly-charmed baryon to be discovered at the LHCb experiment at CERN. We also predict masses of other doubly-charmed strange baryons with quantum numbers 3/2+, 1/2-, and 3/2-.
We present evidence for the existence of a bound H-dibaryon, an I=0, J=0, s=-2 state with valence quark structure uuddss, at a pion mass of m_pi ~ 389 MeV. Using the results of Lattice QCD calculations performed on four ensembles of anisotropic clover gauge-field configurations, with spatial extents of L ~ 2.0, 2.5, 3.0 and 3.9 fm at a spatial lattice spacing of b ~ 0.123 fm, we find an H-dibaryon bound by B = 16.6 +- 2.1 +- 4.6 MeV at a pion mass of m_pi ~ 389 MeV.
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