Masses, magnetic moments and color-spin structures of nonstrange and strange tetraquarks with two heavy quarks are systematically studied in QCD string picture with chromomagnetic interaction. Our mass computations combined with weak and radiative decays indicate that there are two doubly-heavy tetraquarks, the bottom-charmed tetraquark T₂₁ (7173, 01^+) ⁰ and the doubly-bottom tetraquark T₁₁ (10406, 01^+) ^-, to be stable against the strong decay, having the lifetimes of 0. 069 fs and 326 fs, respectively. Magnetic moments are also computed and found to be sensitive to chromomagnetic mixing of the color-spin configurations of these tetraquarks, being valuable probe to experimentally detect the nontrivial color configuration 6₂6₂.
Zhang et al. (Wed,) studied this question.