Dynamical origin and the pole structure of X(3872)

Scalar and Tensor Charmonium Resonances in Coupled-Channel Scattering from Lattice QCD

We determine J^{PC}=0^{++} and 2^{++} hadron-hadron scattering amplitudes in the charmonium energy region up to 4100 MeV using lattice QCD, a first-principles approach to QCD. Working at m_{π}≈391  MeV, more than 200 finite-volume energy levels are computed and these are used in extensions of the Lüscher formalism to determine infinite-volume coupled-channel scattering amplitudes. We find that this energy region contains a single χ_{c0} and a single χ_{c2} resonance. Both are found as pole singularities on the closest unphysical Riemann sheet, just below 4000 MeV with widths around 70 MeV. The largest couplings are to kinematically closed D^{*}D[over ¯]^{*} channels in S-wave, and couplings to several decay channels consisting of pairs of open-charm mesons are found to be large and significant in both cases. Above the ground state χ_{c0}, no other scalar bound states or near-DD[over ¯] threshold resonances are found, in contrast to several theoretical and experimental studies.

Dynamical Approach to Decays of XYZ States

We review the existing results on the exotic XYZ states and their decays obtained within the confined covariant quark model. This dynamical approach is based on a non-local Lagrangian of hadrons with quarks, has built-in quark confinement, and is suited well for the description of different multiquark states, including the four quark ones. We focus our analysis on the various decay modes of five exotic states, X ( 3872 ) , Z c ( 3900 ) , Y ( 4260 ) , Z b ( 10610 ) , and Z b ′ ( 10650 ) , aiming to clarify their internal quark structures. By considering mostly branching fractions and decay widths using the molecular-type or the tetraquark-type interpolating currents, conclusions about the nature of these particles are drawn: the molecular structure is favored for Z c ( 3900 ) , Z b ( 10610 ) , and Z b ′ ( 10650 ) and the tetraquark for X ( 3872 ) and Y ( 4260 ) .