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

Inspired by the observation of the X(6900) by LHCb and the X(6600) (with mass 6552 ± 10 ± 12 MeV) recently by CMS and ATLAS experiments of the LHC in the di- J / Ψ invariant mass spectrum, we systemically study masses of all ground-state configurations of the hidden heavy-flavor tetraquarks q 1 Q 2 q ¯ 3 Q ¯ 4 and Q 1 Q 2 Q ¯ 3 Q ¯ 4 (Q = c , b ; 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 + + ground states of hidden-charm tetraquark c c c ¯ c ¯ with computed masses 6572 MeV, which has a 0 + + color partner around 6469 MeV. The fully bottom system of tetraquark b b b ¯ b ¯ has masses of 19685 MeV and 19717 MeV for the 0 + + ground states. Further calculation of the tetraquark systems s c s ¯ c ¯ , s b s ¯ b ¯ , c b c ¯ b ¯ , n c n ¯ c ¯ and n b n ¯ b ¯ shows that Z c (4200) is a 1 + - state of tetraquark n c n ¯ c ¯ and Z(4020) is a 1 + - state of tetraquark 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. [ABSTRACT FROM AUTHOR]