Doubly heavy tetraquark resonant states

Spectrum of the doubly heavy tetraquarks, bbq¯q¯, is studied in a constituent quark model. Four-body problem is solved in a variational method where the real scaling technique is used to identify resonant states above the fall-apart decay thresholds. In addition to the two bound states that were reported in the previous study we have found several narrow resonant states above the BB^⁎ and B^⁎B^⁎ thresholds. Their structures are studied and are interpreted by the quark dynamics. A narrow resonance with spin-parity J^P=1⁺ is found to be a mixed state of a compact tetraquark and a B^⁎B^⁎ scattering state. This is driven by a strong color Coulombic attraction between the bb quarks. Negative-parity excited resonances with J^P=0⁻, 1⁻ and 2⁻ form a triplet under the heavy-quark spin symmetry. It turns out that they share a similar structure to the λ-mode of a singly heavy baryon as a result of the strongly attractive correlation for the doubly heavy diquark.