Discovery of doubly-charmed Xi_{cc} baryon implies a stable (b b ubar dbar) tetraquark

Abstract

Recently LHCb discovered the first doubly-charmed baryon ${\Xi }_{cc}^{++}=ccu$ at $3621.40\pm 0.78$ MeV, very close to our theoretical prediction. We use the same methods to predict a doubly-bottom tetraquark $T(bb\bar{u}\bar{d})$ with $J^P=1^{+}$ at $10,389\pm 12$ MeV, 215 MeV below the $B^{-}{\bar{B}}^{\ast 0}$ threshold and 170 MeV below threshold for decay to $B^{-}{\bar{B}}^0\gamma$. The $T(bb\bar{u}\bar{d})$ is therefore stable under strong and electromagnetic (EM) interactions and can only decay weakly, the first exotic hadron with such a property. On the other hand, the mass of $T(cc\bar{u}\bar{d})$ with $J^P=1^{+}$ is predicted to be $3882\pm 12$ MeV, 7 MeV above the $D^0{D}^{\ast +}$ threshold and 148 MeV above $D^0{D}^{+}\gamma$ threshold. $T(bc\bar{u}\bar{d})$ with $J^P=0^{+}$ is predicted at $7134\pm 13$ MeV, 11 MeV below the ${\bar{B}}^0{D}^0$ threshold. Our precision is not sufficient to determine whether $bc\bar{u}\bar{d}$ is actually above or below the threshold. It could manifest itself as a narrow resonance just at threshold.

Comments: References added, typos corrected, plot updated. Conclusions unchanged