We report on recent results for the spectrum of heavy quarkonia. Using coarse and anisotropic lattices we achieved an unprecedented control over statistical and systematic errors for higher excited states such as exotic hybrid states. In a parallel study on isotropic lattices we also investigate the effect of two dynamical flavours on the spin structure of charmonium and bottomonium for several symmetric lattices.
We study in detail the spectrum of heavy quarkonia with different orbital angular momentum along with their radial and gluonic excitations. Using an anisotropic formulation of Lattice QCD we achieved an unprecedented control over statistical errors and were able to study systematic errors such as lattice spacing artefacts, finite volume effects and relativistic corrections. First results on the spin structure in heavy hybrids are also presented.
We report on new results for the spectrum of quarkonia using a fully relativistic approach on anisotropic lattices with quark masses in the range from strange to bottom. A fine temporal discretisation also enables us to resolve excitations high above the ground state. In particular we studied the mass dependence and scaling of hybrid states.
We report on a study of heavy hybrid states using the NRQCD approach on coarse and asymmetric lattices, where we discard vacuum polarisation effects and neglect all spin-correction terms. We find a clear hybrid signal on all our lattices ($a_s= 0.15 ... 0.47$ fm). We have studied in detail the lattice spacing artefacts, finite volume effects and mass dependence. Within the above approximations we predict the hybrid excitation in Charmonium to be 1.323(13) GeV above its ground state. The bottomonium hybrid was found to be 1.542(8) GeV above its ground state.
We report on our results from a fully relativistic simulation of the quenched bottomonium spectrum. Using an anisotropic formulation of Lattice QCD, we were able to retain a very fine resolution into the temporal direction for a range of different lattice spacings. At fixed renormalized anisotropy we study the scaling properties of the spectrum and compare our results with non-relativistic calculations.
We report on a first relativistic calculation of the quenched bottomonium spectrum from anisotropic lattices. Using a very fine discretisation in the temporal direction we were able to go beyond the non-relativistic approximation and perform a continuum extrapolation of our results from five different lattice spacings (0.04-0.17 fm) and two anisotropies (4 and 5). We investigate several systematic errors within the quenched approximation and compare our results with those from non-relativistic simulations.