Exploring fully heavy scalar tetraquarks $QQ\overline{Q}\overline{Q}$

Abstract

The masses, current couplings and widths of the fully heavy scalar tetraquarks $X_{4Q}=QQ\overline{Q}\overline{Q}$, $Q=c,b$ are calculated by modeling them as four-quark systems composed of axial-vector diquark and antidiquark. The masses $m^{(\prime )}$ and couplings $f^{(\prime )}$ of these tetraquarks are computed in the context of the QCD sum rule method by taking into account a nonperturbative term proportional to the gluon condensate $⟨{\alpha }_s{G}^2/\pi ⟩$. Results $m=(6570\pm 55)\mathrm{MeV}$ and $m^{\prime }=(18540\pm 50)\mathrm{MeV}$ are used to fix kinematically allowed hidden-flavor decay channels of these states. It turns out that, the processes $X_{4c}\to J/\psi J/\psi$, $X_{4c}\to {\eta }_c{\eta }_c$, and $X_{4c}\to {\eta }_c{\chi }_{c1}(1P)$ are possible decay modes of $X_{4c}$. The partial widths of these channels are evaluated by means of the couplings $g_i,i=1,2,3$ which describe strong interactions of tetraquark $X_{4c}$ and mesons at relevant vertices. The couplings $g_i$ are extracted from the QCD three-point sum rules by extrapolating corresponding form factors $g_i(Q^2)$ to the mass-shell of a final meson. The mass of the scalar tetraquark $X_{4b}$ is below the ${\eta }_b{\eta }_b$ and ${\rm Y}(1S){\rm Y}(1S)$ thresholds, therefore it does not fall apart to these bottomonia, but transforms to conventional particles through other mechanisms. Comparing $m=(6570\pm 55)\mathrm{MeV}$ and ${\Gamma }_{4c}=(110\pm 21)\mathrm{MeV}$ with parameters of structures observed by the LHCb, ATLAS and CMS collaborations, we interpret $X_{4c}$ as the resonance $X(6600)$ reported by CMS. Comparisons are made with other theoretical predictions.

arXiv comment13 Pages, 4 Figures and 2 Tables

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• Investigation of Mass and Decay Characteristics of the Light-Strange Tetraquark
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