We discuss in general the construction of gauge-invariant non-local meson operators on the lattice. We use such operators to study the $P$- and $D$-wave mesons as well as hybrid mesons in quenched QCD, with quark masses near the strange quark mass. The resulting spectra are compared with experiment for the orbital excitations. For the states produced by gluonic excitations (hybrid mesons) we find evidence of mixing for non-exotic quantum numbers. We give predictions for masses of the spin-exotic hybrid mesons with $J^{PC}=1^{-+},\ 0^{+-}$, and $2^{+-}$.Comment: 31 pages, LATEX, 8 postscript figures. Reference adde

Abstract:We calculate the strong isospin breaking and QED corrections to meson masses and the hadronic vacuum polarization in an exploratory study on a 64 × 24 3 lattice with an inverse lattice spacing of a −1 = 1.78 GeV and an isospin symmetric pion mass of m π = 340 MeV. We include QED in an electro-quenched setup using two different methods, a stochastic and a perturbative approach. We find that the electromagnetic correction to the leading hadronic contribution to the anomalous magnetic moment of the muon is smaller than 1% for the up quark and 0.1% for the strange quark, although it should be noted that this is obtained using unphysical light quark masses. In addition to the results themselves, we compare the precision which can be reached for the same computational cost using each method. Such a comparison is also made for the meson electromagnetic mass-splittings.

We present a comprehensive study of the masses of pseudoscalar and vector mesons, as well as octet and decuplet baryons computed in O(a)-improved quenched lattice QCD. Results have been obtained using the nonperturbative definition of the improvement coefficient c sw , and also its estimate in tadpole improved perturbation theory. We investigate effects of improvement on the incidence of exceptional configurations, mass splittings, and the parameter J. By combining the results obtained using nonperturbative and tadpole improvement in a simultaneous continuum extrapolation, we can compare our spectral data to experiment. We confirm earlier findings by the CP-PACS Collaboration that the quenched light hadron spectrum agrees with experiment at the 10% level.

Abstract:We report on an exploratory study of domain wall fermions (DWF) as a lattice regularisation for heavy quarks. Within the framework of quenched QCD with the tree-level improved Symanzik gauge action we identify the DWF parameters which minimise discretisation effects. We find the corresponding effective 4d overlap operator to be exponentially local, independent of the quark mass. We determine a maximum bare heavy quark mass of am h ≈ 0.4, below which the approximate chiral symmetry and O(a)-improvement of DWF are sustained. This threshold appears to be largely independent of the lattice spacing. Based on these findings, we carried out a detailed scaling study for the heavy-strange meson dispersion relation and decay constant on four ensembles with lattice spacings in the range 2.0-5.7 GeV. We observe very mild a 2 scaling towards the continuum limit. Our findings establish a sound basis for heavy DWF in dynamical simulations of lattice QCD with relevance to Standard Model phenomenology.

We present an investigation of a gauge invariant smearing technique that allows the construction of smearing functions with arbitrary radial behaviour, by foresaking the space filling nature of traditional smearing techniques. This is applied to both heavy-heavy, heavy-light, and light-light systems with one particular choice of radial "wavefunction" -the hydrogenic solutions -and we find good stability for both fitted masses and amplitudes of the radially excited states. The dependence of the amplitudes on the smearing radius is demonstrated to be well understood, while near optimal smearing radii may be found with extremely low statistics using a property of the smeared-local correlator. The smearing technique is inexpensive since it is non-iterative, achieves a good signal to noise ratio, and can be altered to use wavefunctions from, say, potential models or the BetheSalpether equations in future simulations.