  In lattice QCD, both direct method and HAL QCD method are used to investigate
the two-baryon systems. We show that due to the contamination of the scattering
excited states, it is challenging to measure the eigenenergy from the temporal
correlation in the direct method, while the HAL QCD method can extract the
information of the interaction from both scattering states and ground state by
using the spatial correlation. We examine the systematic uncertainty of the
derivative expansion in the HAL QCD method, which is found to be well under
control at the low energies. By using the time-dependent HAL QCD method, we
study the nucleon($N$)-Omega($\Omega$) system in the $^5$S$_2$ channel with
almost physical quark masses at $m_\pi \simeq 146$ MeV. We find the interaction
is attractive at all distances, which produces a quasi-bound state with the
binding energy 1.54(0.30)($^{+0.04}_{-0.10}$) MeV. We also consider the extra
Coulomb interaction in the $p\Omega^{-}$($^5$S$_2$) system, whose binding
energy becomes 2.46(0.34)($^{+0.04}_{-0.01}$) MeV. $N\Omega$($^5$S$_2$)
dibaryon could be searched through two-particle correlations in the heavy ion
collision experiments.
