Scalar fully-heavy tetraquark states $$QQ^\prime {\bar{Q}} \bar{Q^\prime }$$ in QCD sum rules

Abstract

Very recently, the LHCb Collaboration observed distinct structures with the $$cc{\bar{c}}{\bar{c}}$$ c c c ¯ c ¯ in the $$J/\Psi $$ J / Ψ -pair mass spectrum. In this work, we construct four scalar ($$J^{PC} = 0^{++}$$ J PC = 0 + + ) $$[8_c]_{Q\bar{Q^\prime }}\otimes [8_c]_{Q^\prime {\bar{Q}}}$$ [ 8 c ] Q Q ′ ¯ ⊗ [ 8 c ] Q ′ Q ¯ type currents to investigate the fully-heavy tetraquark state $$Q Q^\prime {\bar{Q}} \bar{Q^\prime }$$ Q Q ′ Q ¯ Q ′ ¯ in the framework of QCD sum rules, where $$Q=c, b$$ Q = c , b and $$Q^\prime = c, b$$ Q ′ = c , b . Our results suggest that the broad structure around 6.2-6.8 GeV can be interpreted as the $$0^{++}$$ 0 + + octet–octet tetraquark states with masses $$6.44\pm 0.11$$ 6.44 ± 0.11 GeV and $$6.52\pm 0.10$$ 6.52 ± 0.10 GeV, and the narrow structure around 6.9 GeV can be interpreted as the $$0^{++}$$ 0 + + octet–octet tetraquark states with masses $$6.87\pm 0.11$$ 6.87 ± 0.11 GeV and $$6.96\pm 0.11$$ 6.96 ± 0.11 GeV, respectively. Extending to the b-quark sector,the masses of their fully-bottom partners are found to be around 18.38-18.59 GeV. Additionally, we also analyze the spectra of the $$[8_c]_{c{\bar{c}}}\otimes [8_c]_{b {\bar{b}}}$$ [ 8 c ] c c ¯ ⊗ [ 8 c ] b b ¯ and $$[8_c]_{c{\bar{b}}}\otimes [8_c]_{b {\bar{c}}}$$ [ 8 c ] c b ¯ ⊗ [ 8 c ] b c ¯ tetraquark states, which lie in the range of 12.51–12.74 GeV and 12.49–12.81 GeV, respectively.

An updated review of the new hadron states

“…More theoretical studies considering both the meson-meson and diquark-antidiquark configurations can be found in Refs. [616,617,618,619], and there also exist some theoretical studies [620,621] taking the two heavy quark-antiquark pairs as the colored clusters.…”

Higher fully-charmed tetraquarks: Radial excitations and P-wave states

“…The experimental results inspired numerous theoretical discussions [39,40,[40][41][42]. The most popular interpretations are the compact tetraquark states [39][40][41][42][43][44][45][46][47][48][49][50]. Other rare interpretations, such as coupled-channel effects of double-charmonium channels [51,52], cc hybrid [53], a Higgs-like boson [54] and so on, are also proposed.…”

All Heavy Tetraquarks: The Dynamical Diquark Model and Other Approaches

“…The broad structure around 6400-6500 MeV lies at the upper limit of where models predict 1S ground states to occur (e.g., Refs. [26,27]). In LHCb's Model I [1], for example, the structure is treated as a superposition of (at least) two resonances, irrespective of quantum numbers.…”