Tetraquark states with open flavors

Abstract

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 $$[8_c]_{\bar{b} s} \otimes [8_c]_{\bar{d} u}$$ tetraquark currents with $$J^P = 0^+$$ , 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 $$m_\mathrm{s}$$ , and in the end we find two possible tetraquark states with masses $$(5.57 \pm 0.15)$$ and $$(5.58 \pm 0.15)$$ GeV. We find that their charmed-partner masses lie in $$(2.54 \pm 0.13)$$ and $$(2.55 \pm 0.13)$$ GeV, respectively, and are hence accessible in experiments like BESIII and Belle.