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 $B^-\bar B^{*0}$ 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 $3882\pm12$ MeV, 7 MeV above the $D^0 D^{*+}$ threshold and 148 MeV above $D^0 D^+ \gamma$ threshold. $T(bc\bar u\bar d)$ with $J^P{=}0^+$ is predicted at $7134\pm13$ 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.