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

Abstract

Inspired by the observation of the X(6900) by LHCb and the X(6600) (with mass 6552pm 10pm 12 MeV) recently by CMS and ATLAS experiments of the LHC in the di-J/varPsi 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} and Q_{1}Q_{2}{bar{Q}}_{3}{bar{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 cc{bar{c}}{bar{c}} with computed masses 6572 MeV, which has a 0^{++} color partner around 6469 MeV. The fully bottom system of tetraquark bb{bar{b}}{bar{b}} has masses of 19685 MeV and 19717 MeV for the 0^{++} ground states. Further calculation of the tetraquark systems sc{bar{s}}{bar{c}}, sb{bar{s}}{bar{b}}, cb{bar{c}}{bar{b}}, nc{bar{n}}{bar{c}} and nb{bar{n}}{bar{b}} shows that Z_{c}(4200) is a 1^{+-} state of tetraquark nc{bar{n}}{bar{c}} and Z(4020) is a 1^{+-} state of tetraquark nc{bar{n}}{bar{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.