The pion-pion scattering phase shift is computed using LapH propagators. The LapH method for computing quark propagators is used to form two-particle correlation functions with a number of different operators. Excited state energies of two-particle states on 2+1 dynamical, anisotropic lattices (Mpi=390 MeV) are computed to determine the phase shift in the isospin-2 channel. The signal for t-to-t diagrams for the isospin-0 channel are also presented to demonstrate the efficacy of the stochastic LapH method which combines LapH with diluted Z4 noise sources.
Progress in calculating scattering phase shifts on $N_f=2+1$ anisotropic clover Wilson lattices is described. The stochastic LapH method facilitates computations in large volumes and for light pion masses. Results for pion masses down to 240 MeV, keeping $m_pi L > 4$, are presented.
Recent results in computing excited-state energies and meson-meson scattering phase shifts in lattice QCD are presented. A stochastic method of treating the low-lying modes of quark propagation that exploits Laplacian Heaviside quark-field smearing makes such studies possible now on large 32^3 x 256 and 48^3 x 128 lattices at near physical pion masses. Levels are identified using a variety of probe interpolating operators, which include both single-hadron and a large number of two-hadron operators.
We present results of phase shift for I=2 $S$-wave $pipi$ system with the Wilson fermions in the quenched approximation. The finite size method proposed by Luscher is employed, and calculations are carried out at $beta=5.9$ ($a^{-1}=1.934(16)$ GeV from $m_rho$) on $24^3 times 60$, $32^3 times 60$, and $48^3 times 60$ lattices.
Progress in computing the spectrum of excited baryons and mesons in lattice QCD is described. Results in the zero-momentum bosonic I=1/2, S=1, T1u symmetry sector of QCD using a correlation matrix of 58 operators are presented. All needed Wick contractions are efficiently evaluated using a stochastic method of treating the low-lying modes of quark propagation that exploits Laplacian Heaviside quark-field smearing. Level identification using probe operators is discussed.
Progress in computing the hadron spectrum in lattice QCD using stochastic LapH quark propaga- tors is described. The stochastic LapH algorithm is a particular quark smearing algorithm that also allows the computation of all-to-all quark propagators. All-to-all quark propagators are required in our approach of using a large set of spatially extended hadron operators and explicit multi- particle operators to access excited states. We report on the progress made in the various isospin channels on 2+1 dynamical, anisotropic lattices generated by the Hadron Spectrum Collaboration.