Near-threshold structures in the Ds plus Ds- mass distribution of the decay B plus ? Ds plus Ds- K

Abstract

Two near-threshold peaking structures with spin-parities JPC = 0++ were recently discovered by the LHCb Collaboration in the D+s D-s invariant mass distribution of the decay B+ -> D+s D-s K+. The first of them is the resonance X(3960), whereas the second one, X0(4140), is a structure with the mass around 4140 MeV. To explore their natures and model them, we study the hadronic molecule M = D+s D-s and calculate its mass, current coupling, and width. The mass and current coupling of the molecule are extracted from the QCD two-point sum rule analyses by taking into account vacuum condensates up to dimension 10. To evaluate its full width, we consider the processes M -> D+s D-s , M -> eta c eta(0), and M -> J=psi phi. Partial widths of these decays are determined by the strong couplings gi; i = 1, 2, 3, 4 at vertices MD+s D-s , M eta c eta(0), and MJ=psi phi. They are computed by means of the three-point sum rule method. Predictions for the mass m = (4117 +/- 85) MeV and width Gamma M = (62 +/- 12) MeV of the molecule M are compared with the corresponding LHCb data, and also with our results for the diquark-antidiquark state X = [cs][c over bar s over bar ]. We argue that the structure X0(4140) may be interpreted as the hadronic molecule D+s D-s , whereas the resonance X(3960) can be identified with the tetraquark X.