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

TL;DR

This paper systematically studies the masses of hidden heavy-flavor tetraquarks using the MIT bag model, providing insights into observed states like X(6600) and predicting masses for various configurations, highlighting their instability against strong decays.

Contribution

The study introduces a comprehensive mass calculation of all ground-state hidden heavy-flavor tetraquarks considering chromomagnetic interactions, offering explanations for observed states and predictions for unobserved ones.

Findings

X(6600) likely the $0^{++}$ $ccar{c}ar{c}$ tetraquark

Predicted masses for $bbar{b}ar{b}$ tetraquarks around 19685-19717 MeV

Identified $Z_c(4200)$ as $ncar{n}ar{c}$ tetraquark with $J^{PC}=1^{+-}$

Abstract

Inspired by the observation of the $X(6900)$ by LHCb and the $X(6600)$ (with mass $6552\pm 10$ $\pm 12$ MeV) recently by CMS and ATLAS experiments of the LHC in the di-$J/\Psi $ 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 $Q_{1}Q_{2}\bar{Q}_{3}\bar{Q}_{4}$ ($Q=c,b$;$q=u,d,s$) contaning 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 the $0^{++}$ ground states. Further computation is given to the tetraquark systems $sc\bar{s}\bar{c}$, $sb\bar{s}\bar{b}$, $cb\bar{c}\bar{b}$, $nc\bar{n}\bar{c}$ and $nb\bar{n}\bar{b}$, suggesting that the $Z_{c}(4200)$ is the tetraquark $nc\bar{n}\bar{c}$ with $J^{PC}=1^{+-}$. All of these tetraquarks are above their lowest thresholds of two mesons and unstable against the strong decays.