Lattice Prediction for Deeply Bound Doubly Heavy Tetraquarks

We investigate the possibility of qq^'bover ¯bover ¯ tetraquark bound states using n₅=2+1 lattice QCD ensembles with pion masses ≃164, 299, and 415 MeV. Motivated by observations from heavy baryon phenomenology, we consider two lattice interpolating operators, both of which are expected to couple efficiently to tetraquark states: one with a diquark-antidiquark and one with a meson-meson structure. Using nonrelativistic QCD to simulate the bottom quarks, we study the udbover ¯bover ¯, ℓsbover ¯bover ¯ channels with ℓ=u, d, and find unambiguous signals for strong-interaction-stable J^P=1^+ tetraquarks. These states are found to lie 189 (10) and 98 (7) MeV below the corresponding free two-meson thresholds.