Tetraquark states with open flavors

In this work, we estimate the masses of tetraquark states with four different flavors by virtue of QCD sum rules, in both b and c sectors. We construct four [8c]b̄ s ⊗ [8c]d̄ u tetraquark currents with JP = 0⁺ , and then we perform an analytic calculation up to dimension eight in the operator product expansion. We keep terms which are linear in the strange quark mass mₛ , and in the end we find two possible tetraquark states with masses (5.57 ± 0.15) and (5.58 ± 0.15) GeV. We find that their charmed-partner masses lie in (2.54 ± 0.13) and (2.55 ± 0.13) GeV, respectively, and are hence accessible in experiments like BESIII and Belle.