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We present results for the spectrum of static-light mesons from Nf=2 lattice QCD. These results were obtained using all-to-all light quark propagators on an anisotropic lattice, yielding an improved signal resolution when compared to more conventional lattice techniques. In particular, we consider the inversion of orbitally-excited multiplets with respect to the `standard ordering, which has been predicted by some quark models.
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We study $I=0$ quarkonium resonances decaying into pairs of heavy-light mesons using static-static-light-light potentials from lattice QCD. To this end, we solve a coupled channel Schrodinger equation with a confined quarkonium channel and channels with a heavy-light meson pair to compute phase shifts and $mbox{T}$ matrix poles for the lightest decay channel. We discuss our results for $S$, $P$, $D$ and $F$ wave states in the context of corresponding experimental results, in particular for $Upsilon(10753)$ and $Upsilon(10860)$.
In previous works we predicted the existence of a $bar b bar b u d$ tetraquark with quantum numbers $I(J^P) = 0(1^+)$ using the static approximation for the $bar b$ quarks and neglecting heavy spin effects. Since the binding energy is of the same order as expected for these heavy spin effects, it is essential to include them in the computation. Here we present a corresponding method and show evidence that binding is only slightly weakened and that the $bar b bar b u d$ tetraquark persists.
Results on semileptonic decay matrix elements of heavy-light mesons and charmonium spectrum and decay constant using a fine quenched lattice are presented.
We present results for the spectrum of light and strange mesons on configurations with two flavors of mass-degenerate Chirally Improved sea quarks. The calculations are performed on seven ensembles of lattice size 16^3x32 at three different gauge couplings and with pion masses ranging from 250 to 600 MeV. To reliably extract excited states, we use the variational method with an interpolator basis containing both gaussian and derivative quark sources. Both conventional and exotic channels up to spin 2 are considered. Strange quarks are treated within the partially quenched approximation. For kaons we investigate the mixing of interpolating fields corresponding to definite C-parity in the SU(3) limit. This enlarged basis allows for an improved determination of the low-lying kaon spectrum. In addition to masses we also extract the ratio of the pseudoscalar decay constants of the kaon and pion and obtain F_K/F_pi=1.215(41). The results presented here include some ensembles from previous publications and the corresponding results supersede the previously published values.
The electromagnetic form factors provide important insight into the internal structure of the nucleon and continue to be of major interest for experiment and phenomenology. For an intermediate range of momenta the form factors can be calculated on the lattice. However, the reliability of the results is limited by systematic errors mostly due to the required extrapolation to physical quark masses. Chiral effective field theories predict a rather strong quark mass dependence in a range which was yet inaccessible for lattice simulations. We give an update on recent results from the QCDSF collaboration using gauge configurations with dynamical Nf=2, non-perturbatively O(a)-improved Wilson fermions at pion masses as low as 350 MeV.
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