922 research outputs found
Form factors for semi-leptonic B decays
We report on form factors for the B->K l^+ l^- semi-leptonic decay process.
We use several lattice spacings from a=0.12 fm down to 0.06 fm and a variety of
dynamical quark masses with 2+1 flavors of asqtad quarks provided by the MILC
Collaboration. These ensembles allow good control of the chiral and continuum
extrapolations. The b-quark is treated as a clover quark with the Fermilab
interpretation. We update our results for f_\parallel and f_\perp, or,
equivalently, f_+ and f_0. In addition, we present new results for the tensor
form factor f_T. Model independent results are obtained based upon the
z-expansion.Comment: 7 pages, 4 figures, presented at The XXXth International Symposium on
Lattice Field Theory - Lattice 2012, June 24-29, 2012 Cairns, Australia, to
appear as PoS(Lattice 2012)12
Semileptonic B to D decays at nonzero recoil with 2+1 flavors of improved staggered quarks
The Fermilab Lattice-MILC collaboration is completing a comprehensive program
of heavy-light physics on the MILC (2+1)-flavor asqtad ensembles with lattice
spacings as small as 0.045 fm and light-to-strange-quark mass ratios as low as
1/20. We use the Fermilab interpretation of the clover action for heavy valence
quarks and the asqtad action for light valence quarks. The central goal of the
program is to provide ever more exacting tests of the unitarity of the CKM
matrix. We give a progress report on one part of the program, namely the
analysis of the semileptonic decay B to D at both zero and nonzero recoil.
Although final results are not presented, we discuss improvements in the
analysis methods, the statistical errors, and the parameter coverage that we
expect will lead to a significant reduction in the final error for |V_cb| from
this decay channel.Comment: 7 pages, 3 figures, LATTICE 2011 conferenc
Topological susceptibility with the asqtad action
Chiral perturbation theory predicts that in quantum chromodynamics (QCD),
light dynamical quarks suppress the gauge-field topological susceptibility of
the vacuum. The degree of suppression depends on quark multiplicity and masses.
It provides a strong consistency test for fermion formulations in lattice QCD.
Such tests are especially important for staggered fermion formulations that
lack a full chiral symmetry and use the "fourth-root" procedure to achieve the
desired number of sea quarks. Over the past few years we have measured the
topological susceptibility on a large database of 18 gauge field ensembles,
generated in the presence of 2+1 flavors of dynamical asqtad quarks with up and
down quark masses ranging from 0.05 to 1 in units of the strange quark mass and
lattice spacings ranging from 0.045 fm to 0.12 fm. Our study also includes
three quenched ensembles with lattice spacings ranging from 0.06 to 0.12 fm. We
construct the topological susceptibility from the integrated point-to-point
correlator of the discretized topological charge density F-Fdual. To reduce its
variance, we model the asymptotic tail of the correlator. The continuum
extrapolation of our results for the topological susceptibility agrees nicely
at small quark mass with the predictions of lowest-order SU(3) chiral
perturbation theory, thus lending support to the validity of the fourth-root
procedure.Comment: 28 pp, 6 figs. Version 2 corrects some discussion, some numbers, and
some figures and adds some reference
Finite-volume effects and the electromagnetic contributions to kaon and pion masses
We report on the MILC Collaboration calculation of electromagnetic effects on
light pseudoscalar mesons. The simulations employ asqtad staggered dynamical
quarks in QCD plus quenched photons, with lattice spacings varying from 0.12 to
0.06 fm. Finite volume corrections for the MILC realization of lattice
electrodynamics have been calculated in chiral perturbation theory and applied
to the lattice data. These corrections differ from those calculated by Hayakawa
and Uno because our treatment of zero modes differs from theirs. Updated
results for the corrections to "Dashen's theorem" are presented.Comment: 7 pages, 2 figures. Presented at Lattice 2014, Columbia University,
June 23-28, 201
Symanzik flow on HISQ ensembles
We report on a scale determination with gradient-flow techniques on the HISQ ensembles generated by the MILC collaboration. The lattice
scale , originally proposed by the BMW collaboration, is computed using
Symanzik flow at four lattice spacings ranging from 0.15 to 0.06 fm. With a
Taylor series ansatz, the results are simultaneously extrapolated to the
continuum and interpolated to physical quark masses. We give a preliminary
determination of the scale in physical units, along with associated
systematic errors, and compare with results from other groups. We also present
a first estimate of autocorrelation lengths as a function of flowtime for these
ensembles.Comment: 7 pages, 6 pdf figures, 2 tables, presented at the 31st International
Symposium on Lattice Field Theory (Lattice 2013), 29 July - 3 August 2013,
Mainz, German
Lattice QCD ensembles with four flavors of highly improved staggered quarks
We present results from our simulations of quantum chromodynamics (QCD) with
four flavors of quarks: u, d, s, and c. These simulations are performed with a
one-loop Symanzik improved gauge action, and the highly improved staggered
quark (HISQ) action. We are generating gauge configurations with four values of
the lattice spacing ranging from 0.06 fm to 0.15 fm, and three values of the
light quark mass, including the value for which the Goldstone pion mass is
equal to the physical pion mass. We discuss simulation algorithms, scale
setting, taste symmetry breaking, and the autocorrelations of various
quantities. We also present results for the topological susceptibility which
demonstrate the improvement of the HISQ configurations relative to those
generated earlier with the asqtad improved staggered action.Comment: 43 pages, 11 postscript figures, 15 tables, minor changes in text,
version published in Phys. Rev.
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