234 research outputs found
Lattice QCD meets experiment in hadron physics
We review recent results in lattice QCD from numerical simulations that allow
for a much more realistic QCD vacuum than has been possible before. Comparison
with experiment for a variety of hadronic quantities gives agreement to within
statistical and systematic errors of 3%. We discuss the implications of this
for future calculations in lattice QCD, particularly those which will provide
input for B factory experiments.Comment: Review talk at HADRON2003, Aschaffenberg, Germany, September 200
B_s Mesons using Staggered Light Quarks
Last year we proposed using staggered fermions as the light quarks, combined
with nonrelativistic heavy quarks, in simulations of heavy-light mesons. A
first round of tests which focuses on the B_s meson has been completed using
quenched lattices, and results are presented here for the kinetic B_s mass, the
B_s^* - B_s splitting, and f_{B_s}. The next project, already underway, is to
compute the B and B_s decay constants and spectra on the n_f = 2+1 and 3 MILC
lattices. We report on progress with one set of these configurations.Comment: Talk presented by M.W. at Lattice2002(heavyquark
semileptonic decay using lattice QCD with HISQ at physical pion masses
The quark flavor sector of the Standard Model is a fertile ground to look for
new physics effects through a unitarity test of the Cabbibo-Kobayashi-Maskawa
(CKM) matrix. We present a lattice QCD calculation of the scalar and the vector
form factors (over a large region including ) associated with
the semi-leptonic decay. This calculation will then
allow us to determine the central CKM matrix element, in the Standard
Model, by comparing the lattice QCD results for the form factors and the
experimental decay rate. This form factor calculation has been performed on the
MILC HISQ ensembles with the physical light quark masses.Comment: Proceedings for the 35th International Symposium on Lattice Field
Theory (Lattice 2017), 8 pages, 5 figure
Taste-Changing in Staggered Quarks
We present results from a systematic perturbative investigation of
taste-changing in improved staggered quarks. We show one-loop taste-changing
interactions can be removed perturbatively by an effective four-quark term and
calculate the necessary coefficients.Comment: 3 pages using espcrc2.sty and amsmath.sty, 1 Feynman diagram using
feynmp.sty for Lattice2002(improve
B semileptonic decays with 2+1 dynamical quark flavors
We study semileptonic B decays, using MILC dynamical configurations with
. NRQCD heavy and AsqTad light quark actions are used. We obtain the
semileptonic form factors and in the chiral limit.Comment: 6 pages, 3 figures, talk presented at Lattice 2005 (Heavy quark
physics
Light meson form factors at high from lattice QCD
Measurements and theoretical calculations of meson form factors are essential
for our understanding of internal hadron structure and QCD, the dynamics that
bind the quarks in hadrons. The pion electromagnetic form factor has been
measured at small space-like momentum transfer ~GeV by pion
scattering from atomic electrons and at values up to ~GeV by
scattering electrons from the pion cloud around a proton. On the other hand, in
the limit of very large (or infinite) , perturbation theory is
applicable. This leaves a gap in the intermediate where the form factors
are not known.
As a part of their 12 GeV upgrade Jefferson Lab will measure pion and kaon
form factors in this intermediate region, up to of ~GeV. This is
then an ideal opportunity for lattice QCD to make an accurate prediction ahead
of the experimental results. Lattice QCD provides a from-first-principles
approach to calculate form factors, and the challenge here is to control the
statistical and systematic uncertainties as errors grow when going to higher
values.
Here we report on a calculation that tests the method using an
meson, a 'heavy pion' made of strange quarks, and also present preliminary
results for kaon and pion form factors. We use the ensembles made
by the MILC collaboration and Highly Improved Staggered Quarks, which allows us
to obtain high statistics. The HISQ action is also designed to have small
discretisation errors. Using several light quark masses and lattice spacings
allows us to control the chiral and continuum extrapolation and keep systematic
errors in check.Comment: Presented at Lattice 2017, the 35th International Symposium on
Lattice Field Theory at Granada, Spain (18-24 June 2017
Progress Calculating Decay Constants with NRQCD and AsqTad Actions
We combine a light AsqTad antiquark with a nonrelativistic heavy quark to
compute the decay constants of heavy-light pseudoscalar mesons using the
ensemble of 3-flavor gauge field configurations generated by the MILC
collaboration. Preliminary results for and are given and
status of the chiral extrapolation to is reported. We also touch upon
results of the perturbative calculation which matches matrix elements in the
effective theory to the full theory at 1-loop order.Comment: Talk delivered at Lattice2003(heavy), 3 page
Nonperturbative tests of the renormalization of mixed clover-staggered currents in lattice QCD
The Fermilab Lattice and MILC collaborations have shown in one-loop lattice QCD perturbation theory that the renormalization constants of vector and axial-vector mixed clover-asqtad currents are closely related to the product of those for clover-clover and asqtad-asqtad (local) vector currents. To be useful for future higher precision calculations this relationship must be valid beyond one-loop and very general. We test its validity nonperturbatively using clover and Highly Improved Staggered (HISQ) strange quarks, utilising the absolute normalization of the HISQ temporal axial current. We find that the renormalization of the mixed current differs from the square root of the product of the pure HISQ and pure clover currents by 2−3%. We also compare discretization errors between the clover and HISQ formalisms
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