Mass spectra of hidden heavy-flavor tetraquarks with two and four heavy quarks

Abstract

Abstract Inspired by the observation of the X(6900) by LHCb and the X(6600) (with mass $$6552\pm 10\pm 12$$ 6552 ± 10 ± 12 MeV) recently by CMS and ATLAS experiments of the LHC in the di- $$J/\varPsi $$ J / Ψ invariant mass spectrum, we systemically study masses of all ground-state configurations of the hidden heavy-flavor tetraquarks $$q_{1}Q_{2}{\bar{q}}_{3}{\bar{Q}}_{4}$$ q 1 Q 2 q ¯ 3 Q ¯ 4 and $$Q_{1}Q_{2}{\bar{Q}}_{3}{\bar{Q}}_{4}$$ Q 1 Q 2 Q ¯ 3 Q ¯ 4 $$(Q=c,b$$ ( Q = c , b ; $$q=u,d,s)$$ q = u , d , s ) containing two and four heavy quarks in the MIT bag model with chromomagnetic interaction and enhanced binding energy. Considering color-spin mixing due to chromomagnetic interaction, our mass computation indicates that the observed X(6600) is likely to be the $$0^{++}$$ 0 + + ground states of hidden-charm tetraquark $$cc{\bar{c}}{\bar{c}}$$ c c c ¯ c ¯ with computed masses 6572 MeV, which has a $$0^{++}$$ 0 + + color partner around 6469 MeV. The fully bottom system of tetraquark $$bb{\bar{b}}{\bar{b}}$$ b b b ¯ b ¯ has masses of 19685 MeV and 19717 MeV for the $$0^{++}$$ 0 + + ground states. Further calculation of the tetraquark systems $$sc{\bar{s}}{\bar{c}}$$ s c s ¯ c ¯ , $$sb{\bar{s}}{\bar{b}}$$ s b s ¯ b ¯ , $$cb{\bar{c}}{\bar{b}}$$ c b c ¯ b ¯ , $$nc{\bar{n}}{\bar{c}}$$ n c n ¯ c ¯ and $$nb{\bar{n}}{\bar{b}}$$ n b n ¯ b ¯ shows that $$Z_{c}(4200)$$ Z c ( 4200 ) is a $$1^{+-}$$ 1 + - state of tetraquark $$nc{\bar{n}}{\bar{c}}$$ n c n ¯ c ¯ and Z(4020) is a $$1^{+-}$$ 1 + - state of tetraquark $$nc{\bar{n}}{\bar{c}}$$ n c n ¯ c ¯ with a mass of 4079 MeV. All of these tetraquarks are above their lowest thresholds of two mesons and unstable against the strong decays.