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Steven Gottlieb

Publications and source records attributed to Steven Gottlieb.

At least 181 records · Page 10Linked to original sources
arXiv2004

Heavy-light decay constants using clover valence quarks and three flavors of dynamical improved staggered quarks

Starting in 2001, the MILC Collaboration began a large scale calculation of heavy-light meson decay constants using clover valence quarks on ensembles of three flavor configurations. For the coarse configurations, with a=0.12 fm, eight combinations of dynamical light and strange quarks have been analyzed. For the fine configurations, with a=0.09 fm, three combinations of quark masses are studied. Since we last reported on this calculation, statistics have been increased on the fine ensembles, and, more importantly, a preliminary value for the perturbative renormalization of the axial-vector current has become available. Thus, results for f_B, f_{B_s}, f_D and f_{D_s} can, in principle, be calculated in MeV, in addition to decay-constant ratios that were calculated previously.

hep-lat↗
arXiv2004

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

We compute the strange quark mass $m_s$ and the average of the $u$ and $d$ quark masses $\hat m$ using full lattice QCD with three dynamical quarks combined with experimental values for the pion and kaon masses. The simulations have degenerate $u$ and $d$ quarks with masses $m_u=m_d\equiv \hat m$ as low as $m_s/8$, and two different values of the lattice spacing. The bare lattice quark masses obtained are converted to the $\msbar$ scheme using perturbation theory at $O(alpha_s)$. Our results are: $m_s^\msbar$(2 GeV) = 76(0)(3)(7)(0) MeV, $\hat m^\msbar$(2 GeV) = 2.8(0)(1)(3)(0) MeV and $m_s/\hat m$ = 27.4(1)(4)(0)(1), where the errors are from statistics, simulation, perturbation theory, and electromagnetic effects, respectively.

hep-lat↗
arXiv2004

Semileptonic D->pi/K and B->pi/D decays in 2+1 flavor lattice QCD

We present results for form factors of semileptonic decays of $D$ and $B$ mesons in 2+1 flavor lattice QCD using the MILC gauge configurations. With an improved staggered action for light quarks, we successfully reduce the systematic error from the chiral extrapolation. The results for $D$ decays are in agreement with experimental ones. The results for B decays are preliminary. Combining our results with experimental branching ratios, we then obtain the CKM matrix elements $|V_{cd}|$, $|V_{cs}|$, $|V_{cb}|$ and $|V_{ub}|$. We also check CKM unitarity, for the first time, using only lattice QCD as the theoretical input.

hep-lat↗
arXiv2004

Three Flavor QCD at High Temperatures

We have continued our study of the phase diagram of high temperature QCD with three flavors of improved staggered quarks. We are performing simulations with three degenerate quarks with masses less than or equal to the strange quark mass m_s and with degenerate up and down quarks with masses m_{u,d} less than the strange quark mass. For the quark masses studied to date, we find a crossover that strengthens as m_{u,d} decreases, rather than a bona fide phase transition. We present new results for the crossover temperature extrapolated to the physical value of m_{u,d}, and for quark number susceptibilities.

hep-lat↗
arXiv2004

Topological susceptibility with three flavors of staggered quarks

As one test of the validity of the staggered-fermion fourth-root determinant trick, we examine the suppression of the topological susceptibility of the QCD vacuum in the limit of small quark mass. The suppression is sensitive to the number of light sea quark flavors. Our study is done in the presence of 2+1 flavors of dynamical quarks in the improved staggered fermion formulation. Variance-reduction techniques provide better control of statistical errors. New results from staggered chiral perturbation theory account for taste-breaking effects in the low-quark mass behavior of the susceptibility, thereby reducing scaling violations from this source. Measurements over a range of quark masses at two lattice spacings permit a rough continuum extrapolation to remove the remaining lattice artifacts. The results are consistent with chiral perturbation theory with the correct flavor counting.

hep-lat↗
arXiv2004

Results for light pseudoscalars from three-flavor simulations

We compute pseudoscalar meson masses and decay constants in partially quenched QCD with three dynamical flavors of improved staggered quarks. Fitting the lattice data to staggered chiral perturbation theory forms and extrapolating in quark mass and lattice spacing, we find: $f_π= 129.5 \pm 0.9 \pm 3.5$ MeV, $f_K = 156.6 \pm 1.0 \pm 3.6$ MeV, and $f_K/f_π= 1.210(4)(13)$. The value for $f_K/f_π$ implies $|V_{us}|=0.2219(26)$. We also obtain $m_u/m_d = 0.43(0)(1)(8)$, or, with more input on electromagnetic effects from the continuum, $m_u/m_d = 0.41(0)(1)(4)$. Using the one-loop perturbative mass renormalization, we determine $m_u$ and $m_d$ in the MSbar scheme.

hep-lat↗
arXiv2004

Semileptonic decays of $D$ mesons in three-flavor lattice QCD

We present the first three-flavor lattice QCD calculations for $D\to πlν$ and $D\to K lν$ 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 $q^2=0$ are $f_+^{D\toπ}(0)=0.64(3)(6)$ and $f_+^{D\to K}(0) = 0.73(3)(7)$, where the first error is statistical and the second is systematic, added in quadrature. Combining our results with experimental branching ratios, we obtain the CKM matrix elements $|V_{cd}|=0.239(10)(24)(20)$ and $|V_{cs}|=0.969(39)(94)(24)$, where the last errors are from experimental uncertainties.

hep-ph↗
arXiv2004

Light hadrons with improved staggered quarks: approaching the continuum limit

We 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 approximately 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 effects of decays, or coupling to two-meson states, in the 0++, 1+, and 0- meson propagators, and we make a preliminary mass computation for a radially excited 0- meson.

hep-lat↗
arXiv2003

www.fermiqcd.net

A quick review of the features of FermiQCD, a C++ library for fast development of parallel Lattice QCD applications. FermiQCD is fully Object Oriented and is based on MPI but, it required no previsius knowledge of parallel programming. It includes parallel algorithms for Wilson, Clover, Staggered, Asqtad and Domain Wall fermions. Optimizations are based on M. Luescher's SSE2 macros.

hep-lat↗
arXiv2003

Lattice calculation of $1^{-+}$ hybrid mesons with improved Kogut-Susskind fermions

We 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 $π_1(1600)$.

hep-lat↗
arXiv2003

D_s spectrum and leptonic decays with Fermilab heavy quarks and improved staggered light quarks

We present preliminary results for the D_s meson spectrum and decay constants in unquenched lattice QCD. Simulations are carried out with 2+1 dynamical quarks using gauge configurations generated by the MILC collaboration. We use the ``asqtad'' a^2 improved staggered action for the light quarks, and the clover heavy quark action with the Fermilab interpretation. We compare our spectrum results with the newly discovered 0+ and 1+ states in the D_s system.

hep-lat↗
arXiv2003

Results on improved KS dynamical configurations: spectrum, decay constants, etc

The MILC Collaboration has been producing ensembles of lattice configurations with three dynamical flavors for the past few years. There are now results for three lattice spacings for a variety of light and strange quark masses, ranging down to $m_l=0.1 m_s$, where $m_s$ is the dynamical strange quark mass and $m_l$ is the common mass of the $u$ and $d$ quarks. Recently, the Fermilab, HPQCD, MILC and UKQCD collaborations have presented a summary of results obtained using these lattices. Compared with quenched results, these new calculations show great improvement in agreement with experiment. This talk addresses the technical improvements that make these calculations possible and provides additional details of calculations not presented in the initial summary. We demonstrate that a wide range of hadronic observables can now be calculated to 2--3% accuracy.

hep-lat↗
arXiv2003

Topological susceptibility with the improved Asqtad action

Chiral perturbation theory predicts that in quantum chromodymamics light dynamical quarks suppress the topological (instanton) susceptibility. We investigate this suppression through direct numerical simulation using the Asqtad improved lattice fermion action. This action holds promise for carrying out nonperturbative simulations over a range of quark masses for which chiral perturbation theory is expected to converge. To test the effectiveness of the action in capturing instanton physics, we measure the topological susceptibility as a function of quark masses with 2+1 dynamical flavors. Our results, when extrapolated to zero lattice spacing, are consistent with predictions of leading order chiral perturbation theory. Included in our study is a comparison of three methods for analyzing the topological susceptibility: (1) the Boulder hypercubic blocking technique with the Boulder topological charge operator, (2) the more traditional Wilson cooling method with the twisted plaquette topological charge operator and (3) the improved cooling method of de Forcrand, Perez, and Stamatescu and their improved topological charge operator.

hep-lat↗
arXiv2003

Excited States in Staggered Meson Propagators

We report on preliminary results from multi-particle fits to meson propagators with three flavors of light dynamical quarks. We are able to measure excited states in propagators with pion quantum numbers, which we interpret as the pion 2S state, and is evidence of locality of the action. In the a_0 (0^{++}) propagators we find evidence for excited states which are probably the expected decay channels, pi+eta and K+Kbar.

hep-lat↗
arXiv2003

Semileptonic decays of $D$ mesons in unquenched lattice QCD

We present our preliminary results for semileptonic form factors of $D$ mesons in unquenched lattice QCD. Simulations are carried out with $n_f=2+1$ dynamical quarks using gauge configurations generated by the MILC collaboration. For the valence quarks, we adopt an improved staggered light quark action and the clover heavy quark action. Our results for $D \to K$ and $D \to π$ form factors at $q^2=0$ are in agreement with the experimental values.

hep-lat↗
arXiv2003

The Phase Diagram of High Temperature QCD with Three Flavors of Improved Staggered Quarks

We report on progress in our study of high temperature QCD with three flavors of improved staggered quarks. Simulations are being carried out with three degenerate quarks with masses less than or equal to the strange quark mass, $m_s$, and with degenerate up and down quarks with masses in the range $0.1 m_s \leq m_{u,d}\leq 0.6 m_s$, and the strange quark mass fixed near its physical value. For the quark masses studied to date we find rapid crossovers, which sharpen as the quark mass is reduced, rather than bona fide phase transitions.

hep-lat↗
arXiv2003

Pion and kaon physics with improved staggered quarks

We compute pseudoscalar meson masses and decay constants using staggered quarks on lattices with three flavors of sea quarks and lattice spacings $\approx 0.12$ fm and $\approx 0.09$ fm. We fit partially quenched results to ``staggered chiral perturbation theory'' formulae, thereby taking into account the effects of taste-symmetry violations. Chiral logarithms are observed. From the fits we calculate $f_π$ and $f_K$, extract Gasser-Leutwyler parameters of the chiral Lagrangian, and (modulo rather large perturbative errors) find the light and strange quark masses.

hep-lat↗