Charmed-meson decay constants in three-flavor lattice QCD

Journal ArticleWe present the first lattice QCD calculation with realistic sea quark content of the D+-meson decay constant fD+. We use the MILC Collaboration's publicly available ensembles of lattice gauge fields, which have a quark sea with two flavors (up and down) much lighter than a third (strange). We obtain fD+ = 201 + 3 + 17 MeV, where the errors are statistical and a combination of systematic errors. We also obtain fDs = 249 + 3 + 16 MeV for the Ds meson

Semileptonic decays of heavy mesons with the fat clover action

ManuscriptWe are studying a variety of semileptonic decays of heavy-light mesons in an effort to improve the determination of the heavy-quark Standard-Model CKM matrix elements. Our fermion action is a novel, improved "fat" clover action that promises to reduce problems with exceptional configurations. Dynamical sea quarks are included in a mixed approach, i.e. we use staggered sea quarks and fat-clover valence quarks. Here we report preliminary results

Light pseudoscalar decay constants, quark masses, and low energy constants from three-flavor lattice QCD

Journal ArticleAs part of our program of lattice simulations of three-flavor QCD with improved staggered quarks, we have calculated pseudoscalar meson masses and decay constants for a range of valence quark masses and sea-quark masses on lattices with lattice spacings of about 0.125 and 0.09 fm. We fit the lattice data to forms computed with ‘‘staggered chiral perturbation theory.'' Our results provide a sensitive test of the lattice simulations, and especially of the chiral behavior, including the effects of chiral logarithms. We find: frr= 129.5 + 0.9 + 3.5 MeV, fK = 156.6 + 1.0 + 3.6 MeV, and fK/frr = 1.210(4)(13), where the errors are statistical and systematic

Quark loop effects in semileptonic form factors for heavy-light mesons

ManuscriptWe present preliminary results of a determination of the semileptonic form factor for the decay of pseudoscalar heavy-light mesons to pseudoscalar light-light mesons in full QCD. In this preliminary study we focus on the effects of dynamical quark loops. Accordingly, we compare results of simulations with matched quenched and Asqtad dynamical gauge configurations. The latter include three flavors of light quarks. Our simulation uses clover Wilson valence quarks, treated in the Fermilab formalism. Preliminary results, as yet uncorrected by continuum matching factors, suggest a measurable enhancement in the form factor due to dynamical quark loops over the accessible range of q2

Semileptonic decays of D mesons in three-flavor lattice QCD

Journal ArticleWe present the first three-flavor lattice QCD calculations for D→ rrlv and D→ Klv semileptonic decays. Simulations are carried out using ensembles of unquenched gauge fields generated by the MILC Collaboration. With an improved staggered action for light quarks, we are able to simulate at light quark masses down to 1=8 of the strange mass. Consequently, the systematic error from the chiral extrapolation is much smaller than in previous calculations with Wilson-type light quarks. Our results for the form factors at q2 = 0 are fD→rr(0)= 0:64(3)(6) and fD→K (0) = 0:73(3)(7), where the first error is statistical and the second is systematic, added in quadrature. Combining our results with experimental branching ratios, we obtain the Cabibbo-Kobayashi-Maskawa matrix elements [Vcd] = 0:239(10)(24)(20) and [Vcs]= 0.969(39)(94)(24), where the last errors are from experimental uncertainties

First determination of the strange and light quark masses from full lattice QCD

Journal ArticleWe compute the strange quark mass ms and the average of the u and d quark masses mˆ using full lattice QCD with three dynamical quarks combined with the experimental values for the rr and K masses. The simulations have degenerate u and d quarks with masses mu=md=mˆ αs low as ms/8, and two different values of the lattice spacing. The bare lattice quark masses obtained are converted to the MS scheme using perturbation theory at O(αS). Our results are ms MS(2 GeV)576(0)(3)(7)(0) MeV, mˆ MS(2 GeV) 52.8(0)(1)(3)(0) MeV, and ms /mˆ =27.4(1)(4)(0)(1), where the errors are from statistics, simulation, perturbation theory, and electromagnetic effects, respectively

Lattice calculation of 1-+ hybrid mesons with improved Kogut-Susskind fermions

Journal ArticleWe report on a lattice determination of the mass of the exotic 1-+ hybrid meson using an improved Kogut-Susskind action. Results from both quenched and dynamical quark simulations are presented. We also compare with earlier results using Wilson quarks at heavier quark masses. The results on lattices with three flavors of dynamical quarks show effects of sea quarks on the hybrid propagators which probably result from coupling to two meson states. We extrapolate the quenched results to the physical light quark mass to allow comparison with experimental candidates for the 1-+ hybrid meson. The lattice result remains somewhat heavier than the experimental result, although it may be consistent with the rr 1 (1600)

QCD equation of state with 2+1 flavors of improved staggered quarks

Journal ArticleWe report results for the interaction measure, pressure, and energy density for nonzero-temperature QCD with 2 + 1 flavors of improved staggered quarks. In our simulations, we use a Symanzik improved gauge action and the Asqtad O(a2) improved staggered quark action for lattices with temporal extent Nt = 4 and 6. The heavy quark mass ms is fixed at approximately the physical strange quark mass and the two degenerate light quarks have masses mud ≈ 0:1ms or 0:2ms. The calculation of the thermodynamic observables employs the integral method where energy density and pressure are obtained by integration over the interaction measure

Light hadrons with improved staggered quarks: approaching the continuum limit

Journal ArticleWe have extended our program of QCD simulations with an improved Kogut-Susskind quark action to a smaller lattice spacing, approximately 0.09 fm. Also, the simulations with a ≈ 0:12 fm have been extended to smaller quark masses. In this paper we describe the new simulations and computations of the static quark potential and light hadron spectrum. These results give information about the remaining dependences on the lattice spacing.We examine the dependence of computed quantities on the spatial size of the lattice, on the numerical precision in the computations, and on the step size used in the numerical integrations.We examine the effects of autocorrelations in ‘‘simulation time'' on the potential and spectrum.We see possible effects of decays, or coupling to two-meson states in the 0++ and 1+ meson propagators. A state consistent with rr + K is seen as a ‘‘parity partner'' in the Goldstone kaon propagator, and we make a preliminary mass computation for a radially excited 0- meson