Narrow Results

Recent BESIII data indicate a significant rate of the process e⁺e^- →h_c π⁺ π^- at the Y(4260) and Y(4360) resonances, implying a substantial breaking of the heavy quark spin symmetry. We consider these resonances within the picture of hadrocharmonium, i.e. of (relatively) compact charmonium embedded in a light-quark mesonic excitation. We suggest that the resonances Y(4260) and Y(4360) are a mixture, with mixing close to maximal, of two states of hadrochamonium, one containing a spin-triplet pair and the other containing a spin-singlet heavy quark pair. We argue that this model is in a reasonable agreement with the available data and produces distinctive and verifiable predictions for the energy dependence of the production rate in e⁺e^- annihilation of the final states J/ψππ, ψ′ππ and h_c ππ, including the pattern of interference between the two resonances.

In this paper, we apply the method of QCD sum rules to study the doubly heavy tetraquark states $QQ\bar{q}\bar{n}$ with spin-parity $J^P=1^{+}$ and strangeness $S=0,-1$ using careful estimates of the Borel and threshold parameters involved. Masses of the doubly bottom and charmed tetraquarks with isospin $I=0,1/2,1$ are computed precisely via taking into account multifarious condensates up to dimension 10. Compared with the two-heavy meson thresholds, we find that all nonstrange doubly-bottom tetraquarks and a doubly-charmed tetraquarks associated with $J_3$ with $J^P=1^{+}$ are stable against strong decay into two bottom mesons while a doubly-charmed tetraquark associated with current $J_2$ is unstable against strong decay. By the way, weak decay widths of the doubly bottom tetraquarks are also given.