Possible Existence of a Deeply BoundΔ−ΔSystem

Being motivated by the observation of an anomaly in the polarization of protons in $\gamma d\to \mathrm{pn}$, we have investigated the possible existence of deeply bound dibaryon states. The nonrelativistic one-boson-exchange potential model ($\pi$, $\eta$, $\rho$, and $\omega$ exchanges) for two $\Delta$ isobars gives binding energies around 100 MeV for $I=0\mathrm{}$, $J=3\mathrm{}$, and $I=3\mathrm{}$, $J=0\mathrm{}$. Existence of this $I=0\mathrm{}$ dibaryon resonance reproduces experimentally observed cross sections in the $I=0\mathrm{}$, $\mathrm{NN}\to d\pi \pi$ and $\mathrm{NN}\to \mathrm{NN}\pi \pi$ channels.