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ABSTRACT: We discuss a new approach to reducing excited state contributions from two- and three-point correlation functions in lattice simulations. For the purposes of this talk, we focus on the Delta(1232) resonance and discuss how this new method reduces excited state contamination from two-point functions and mention how this will be applied to three-point functions to extract hadronic form factors. Comment: 4 pages, 3 figures, talk given at MENU 2010, Williambsurg, VA
10/2010;
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ABSTRACT: We calculate the magnetic dipole moment of the Delta(1232) and Omega^- baryons with 2+1-flavors of clover fermions on anisotropic lattices using a background magnetic field. This is the first dynamical calculation of these magnetic moments using a background field technique. The calculation for Omega^- is done at the physical strange quark mass, with the result in units of the physical nuclear magneton mu_Omega^-= -1.93(8)(12) (where the first error is statistical and the second is systematic) compared to the experimental number: -2.02(5). The Delta has been studied at three unphysical quark masses, corresponding to pion mass m_pi = 366, 438, and 548 MeV. The pion mass dependence is compared with the behavior obtained from chiral effective field theory. Comment: 4 pages, 2 figures, 2 tables, uses RevTeX
11/2008;
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ABSTRACT: We calculate the magnetic dipole moment of the Delta baryon using a background magnetic field on 2+1-flavors of clover fermions on anisotropic lattices. We focus on the finite volume effects that can be significant in background field studies, and thus we use two different spatial volumes in addition to several quark masses. Comment: 7 pages, 2 figures, contributed talk at Lattice 2008, to appear in the proceedings
09/2008;
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ABSTRACT: t O(a ). We use the word avor" for dierent staggered elds; lattice avor symmetry is exact for equal masses. MILC's improved staggered (a -tad") simulations [3] use three elds (u; d; s") and reduce the tastes to one per avor by taking 4 p Det. We call these 2 + 1" avor simulations since we take m u = m d m ` . MILC data for m vs. quark mass show clear deviations from linearity, as expected from chiral logarithms. However, the detailed behavior at a 0:13 fm does not agree with continuum chi- talk presented by C. Bernard at Lattice 2002; to be published in the proceedings ral perturbation theory (PT) [4]. Figure 1 shows a t to the continuum forms for m X =(m 1 + m 2 ), where X = or K, and m 1 , m 2 are quark masses. (We de ne pions" to have m 1 = m 2 and kaons" to have m 2 m phys s and m 1 6= m 2 .) The t is very poor, with a con dence level of 5 10 . To get good ts, one needs to include the O(a taste-breaking eects into the chiral
10/2002;
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ABSTRACT: We present results for $f_B$, $f_{B_s}$, $f_D$, $f_{D_s}$ and their ratios in the presence of two flavors of light sea quarks ($N_f=2$). We use Wilson light valence quarks and Wilson and static heavy valence quarks; the sea quarks are simulated with staggered fermions. Additional quenched simulations with nonperturbatively improved clover fermions allow us to improve our control of the continuum extrapolation. For our central values the masses of the sea quarks are not extrapolated to the physical $u$, $d$ masses; that is, the central values are "partially quenched." A calculation using "fat-link clover" valence fermions is also discussed but is not included in our final results. We find, for example, $f_B = 190 (7) (^{+24}_{-17}) (^{+11}_{-2}) (^{+8}_{-0})$ MeV, $f_{B_s}/f_B = 1.16 (1) (2) (2) (^{+4}_{-0})$, $f_{D_s} = 241 (5) (^{+27}_{-26}) (^{+9}_{-4}) (^{+5}_{-0})$ MeV, and $f_{B}/f_{D_s} = 0.79 (2) (^{+5}_{-4}) (3) (^{+5}_{-0})$, where in each case the first error is statistical and the remaining three are systematic: the error within the partially quenched $N_f=2$ approximation, the error due to the missing strange sea quark and to partial quenching, and an estimate of the effects of chiral logarithms at small quark mass. The last error, though quite significant in decay constant ratios, appears to be smaller than has been recently suggested by Kronfeld and Ryan, and Yamada. We emphasize, however, that as in other lattice computations to date, the lattice $u,d$ quark masses are not very light and chiral log effects may not be fully under control.
07/2002;
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ABSTRACT: We present preliminary results for the heavy-light leptonic decay constants in the presence of three light dynamical flavors. We generate dynamical configurations with improved staggered and gauge actions and analyze them for heavy-light physics with tadpole improved clover valence quarks. When the scale is set by $m_\rho$, we find an increase of approximately 23% in $f_B$ with three dynamical flavors over the quenched case. Discretization errors appear to be small (of order 3% or less) in the quenched case but have not yet been measured in the dynamical case.
11/2001;
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ABSTRACT: a Symanzik improved glue [2,3]. This action has small discretization errors for many quantities [4,5]. For the valence quarks, we employ a tadpole-improved (Landau link) clover action and the Fermilab formalism [6]. The analysis is done in a "partially quenched" manner: the valence quark masses are extrapolated to their physical values with the sea quark masses held fixed. The chiral extrapolation of the sea quark masses (at fixed lattice spacing) is performed afterwards. presented by C. Bernard Table 1 shows the parameters of our lattices and the current state of this project. As we decrease the dynamical quark masses from large values in the three-flavor case, we keep the three masses degenerate until the physical strange quark mass is reached. We then keep the strange quark mass fixed as we further decrease m u;d . Configurations with varying dynamical quark mass (including quenched and two-flavor configurations) have been matched in lattice spacing using the quantity r 1
11/2001;
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ABSTRACT: We present preliminary results from exploring the phase diagram of finite temperature QCD with three degenerate flavors and with two light flavors and the mass of the third held approximately at the strange quark mass. We use an order $\alpha_s^2 a^2, a^4$ Symanzik improved gauge action and an order $\alpha_s a^2, a^4$ improved staggered quark action. The improved staggered action leads to a dispersion relation with diminished lattice artifacts, and hence better thermodynamic properties. It decreases the flavor symmetry breaking of staggered quarks substantially, and we estimate that at the transition temperature for an $N_t=8$ to $N_t=10$ lattice {\em all} pions will be lighter than the lightest kaon. Preliminary results on lattices with $N_t=4$, 6 and 8 are presented.
11/2001;
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ABSTRACT: The separation of a heavy quark and antiquark pair leads to the formation of a tube of flux, or "string", which should break in the presence of light quark-antiquark pairs. This expected zero-temperature phenomenon has proven elusive in simulations of lattice QCD. We study mixing between the string state and the two-meson decay channel in QCD with two flavors of dynamical sea quarks. We confirm that mixing is weak and find that it decreases at level crossing. While our study does not show direct effects of internal quark loops, our results, combined with unitarity, give clear confirmation of string breaking.
04/2001;
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ABSTRACT: We present results for pseudoscalar decay constants of heavy-light mesons using both quenched and N_f = 2 dynamical fermion configurations. A variety of fermion actions is investigated : Wilson, nonperturbative clover, and fat-link clover. For heavy quarks the Fermilab formalism is applied. In the quenched approximation, results with the nonperturbatively improved clover action of the Alpha collaboration allow us to study the systematic error of the continuum extrapolation from the Wilson action. In addition, we use quenched configurations to explore the effects of fattening. The lessons from the quenched analyses are then applied to data with dynamical fermions, where both Wilson and fat-link clover actions have been used. This allows us to attempt a continuum extrapolation of the dynamical results.
12/2000;
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ABSTRACT: We have been studying effects of dynamical quarks on various hadronic observables, using our recently formulated improvement for staggered fermions. To illustrate improvement, we show that the light hadron spectrum in the quenched approximation gives remarkably good scaling. We highlight three new results: (1) We find no apparent quark loop effects in the Edinburgh plot with 2+1 flavors of dynamical quarks at a = 0.14 fm. (2) We show that dynamical quarks modify the shape of the heavy quark potential. (3) We present results hinting at meson decay effects in light hadron spectroscopy.
11/2000;
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ABSTRACT: The separation of a heavy quark and antiquark pair leads to the formation of a tube of flux, or "string", which should break in the presence of light quark-antiquark pairs. This expected zero-temperature phenomenon has proven elusive in simulations of lattice QCD. In an extension of work reported last year we present clear evidence for string breaking in QCD with two flavors of dynamical staggered sea quarks and apply our results to a simple three-state mixing model for string breaking. We find that mixing is weak and falls to zero at level crossing.
11/2000;
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ABSTRACT: We study the effects of dynamical quarks on the static quark potential at distances shorter than those where string breaking is expected. Quenched calculations and calculations with three flavors of dynamical quarks are done on sets of lattices with the lattice spacings matched within about one percent. The effect of the sea quarks on the shape of the potential is clearly visible. We investigate the consequences of these effects in a very crude model, namely solving Schroedinger's equation in the resulting potential. Comment: 20 pages RevTeX, color postscript figures included Table heading fixed, Fig. 4 improved, reference added, lines tightened
02/2000;
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ABSTRACT: Improved lattice actions for Kogut-Susskind quarks have been shown to improve rotational symmetry and flavor symmetry. In this work we find improved scaling behavior of the rho and nucleon masses expressed in units of a length scale obtained from the static quark potential, and better behavior of the Dirac operator in instanton backgrounds.
01/2000;
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ABSTRACT: We study improved Kogut-Susskind fermion actions focusing on flavor symmetry restoration. Several variants of fat actions suitable for dynamical simulations are considered, including an action with no tree level order a-squared errors. The spectrum of all the pions is computed and used as a measure of flavor symmetry violation. Finally, the Naik term is introduced to restore rotational symmetry.
10/1999;
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ABSTRACT: We 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. Comment: LATTICE99(heavyqk) - 3p, 4 Postscript figs
09/1999;
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ABSTRACT: We present results for $f_B$, $f_{B_s}$, $f_D$, $f_{D_s}$ and their ratios in the presence of two flavors of light sea quarks ($N_f=2$). We use Wilson light valence quarks and Wilson and static heavy valence quarks; the sea quarks are simulated with staggered fermions. Additional quenched simulations with nonperturbatively improved clover fermions allow us to improve our control of the continuum extrapolation. For our central values the masses of the sea quarks are not extrapolated to the physical $u$, $d$ masses; that is, the central values are "partially quenched." A calculation using "fat-link clover" valence fermions is also discussed but is not included in our final results. We find, for example, $f_B = 190 (7) (^{+24}_{-17}) (^{+11}_{-2}) (^{+8}_{-0})$ MeV, $f_{B_s}/f_B = 1.16 (1) (2) (2) (^{+4}_{-0})$, $f_{D_s} = 241 (5) (^{+27}_{-26}) (^{+9}_{-4}) (^{+5}_{-0})$ MeV, and $f_{B}/f_{D_s} = 0.79 (2) (^{+5}_{-4}) (3) (^{+5}_{-0})$, where in each case the first error is statistical and the remaining three are systematic: the error within the partially quenched $N_f=2$ approximation, the error due to the missing strange sea quark and to partial quenching, and an estimate of the effects of chiral logarithms at small quark mass. The last error, though quite significant in decay constant ratios, appears to be smaller than has been recently suggested by Kronfeld and Ryan, and Yamada. We emphasize, however, that as in other lattice computations to date, the lattice $u,d$ quark masses are not very light and chiral log effects may not be fully under control.
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ABSTRACT: We present results for pseudoscalar decay constants of heavy-light mesons using both quenched and Nf = 2 dynamical fermion configurations. A variety of fermion actions is investigated: Wilson, nonperturbative clover, and fat-link clover. For heavy quarks the Fermilab formalism is applied. In the quenched approximation, results with the nonperturbatively improved clover action of the Alpha collaboration allow us to study the systematic error of the continuum extrapolation from the Wilson action. In addition, we use quenched configurations to explore the effects of fattening. The lessons from the quenched analyses are then applied to data with dynamical fermions, where both Wilson and fat-link clover actions have been used. This allows us to attempt a continuum extrapolation of the dynamical results.
Nuclear Physics B - Proceedings Supplements.
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ABSTRACT: We describe a calculation of heavy-light decay constants including virtual quark loop effects. We have generated dynamical gauge configurations at three β values using two flavors of Kogut-Susskind quarks with a range of masses. These are analyzed with a Wilson valence quark action. Preliminary results based on a “fat-link” clover valence quark action are also reported. Results from the two methods differ by 30 to 50 MeV, which is presumably due to significant — but as yet unobserved — lattice spacing dependence in one or both of the approaches.
Nuclear Physics B - Proceedings Supplements.
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ABSTRACT: We present preliminary results [1] from exploring the phase diagram of finite temperature QCD with three degenerate flavors and with two light flavors and the mass of the third held approximately at the strange quark mass. We use an order α2sa2, a4 Symanzik improved gauge action and an order αsa2, a4 improved staggered quark action. The improved staggered action leads to a dispersion relation with diminished lattice artifacts, and hence better thermodynamic properties. It decreases the flavor symmetry breaking of staggered quarks substantially, and we estimate that at the transition temperature for an Nt = 8 to Nt = 10 lattice all pions will be lighter than the lightest kaon. Preliminary results on lattices with Nt = 4, 6 and 8 are presented.
Nuclear Physics B - Proceedings Supplements.
