Double-heavy axial-vector tetraquark [formula omitted

Abstract

The mass and coupling of the axial-vector tetraquark Tbc;u¯d¯0 (in a short form Tbc0) are calculated by means of the QCD two-point sum rule method. In computations we take into account contributions arising from various quark, gluon and mixed vacuum condensates up to dimension 10. The central value of the mass m=(7105±155)MeV lies below the thresholds for the strong and electromagnetic decays of the Tbc0 state, and hence it transforms to conventional mesons only through the weak decays. In the case of m=7260MeV the tetraquark Tbc0 becomes the strong- and electromagnetic-interaction unstable particle. In the first case, we find the full width and mean lifetime of Tbc0 using its semileptonic decays Tbc0→Tcc;u¯d¯+lν‾l (l=e,μ,τ), where the final-state tetraquark is a scalar state. We compute also partial widths of the nonleptonic weak decays Tbc0→Tcc;u¯d¯+π−(K−,D−,Ds−), and take into account their effects on the full width of Tbc0. In the context of the second scenario we calculate partial widths of S-wave strong decays Tbc0→B⁎−D+ and Tbc0→B‾⁎0D0, and using these channels evaluate the full width of Tbc0. Predictions for Γfull=(3.98±0.51)×10−10MeV and mean lifetime τ=1.65−0.18+0.25ps of Tbc0 obtained in the context of the first option, as well as the full width Γfull=(63.5±8.9)MeV extracted in the second scenario may be useful for experimental and theoretical exploration of double-heavy exotic mesons.