211 research outputs found
Fast Fits for Lattice QCD Correlators
We illustrate a technique for fitting lattice QCD correlators to sums of
exponentials that is significantly faster than traditional fitting methods ---
10--40 times faster for the realistic examples we present. Our examples are
drawn from a recent analysis of the Upsilon spectrum, and another recent
analysis of the D -> pi semileptonic form factor. For single correlators, we
show how to simplify traditional effective-mass analyses.Comment: 5 pages, 4 figure
Highly Improved Staggered Quarks on the Lattice, with Applications to Charm Physics
We use perturbative Symanzik improvement to create a new staggered-quark
action (HISQ) that has greatly reduced one-loop taste-exchange errors, no
tree-level order a^2 errors, and no tree-level order (am)^4 errors to leading
order in the quark's velocity v/c. We demonstrate with simulations that the
resulting action has taste-exchange interactions that are at least 3--4 times
smaller than the widely used ASQTAD action. We show how to estimate errors due
to taste exchange by comparing ASQTAD and HISQ simulations, and demonstrate
with simulations that such errors are no more than 1% when HISQ is used for
light quarks at lattice spacings of 1/10 fm or less. The suppression of (am)^4
errors also makes HISQ the most accurate discretization currently available for
simulating c quarks. We demonstrate this in a new analysis of the psi-eta_c
mass splitting using the HISQ action on lattices where a m_c=0.43 and 0.66,
with full-QCD gluon configurations (from MILC). We obtain a result of~111(5)
MeV which compares well with experiment. We discuss applications of this
formalism to D physics and present our first high-precision results for D_s
mesons.Comment: 21 pages, 8 figures, 5 table
New results on heavy hadron spectroscopy with NRQCD
We present results for the spectrum of b-bbar bound states in the quenched
approximation for three different values of the lattice spacing. Results for
spin-independent splittings are shown to have good scaling behaviour;
spin-dependent splittings are more sensitive to discretisation effects. We
discuss what needs to be done to match the experimental spectrum.Comment: 3 pages, contribution to Lattice'9
Υ and Υ′ leptonic widths, abμ, and mb from full lattice QCD
We determine the decay rate to leptons of the ground-state Ï’ meson and its first radial excitation in lattice
QCD for the first time. We use radiatively improved nonrelativistic QCD for the b quarks and include u, d,
s and c quarks in the sea with u=d masses down to their physical values. We find Γðϒ → eþe−Þ ¼
1.19ð11Þ keV and Γðϒ0 → eþe−Þ ¼ 0.69ð9Þ keV, both in good agreement with experimental results. The
decay constants we obtain are included in a summary plot of meson decay constants from lattice QCD
given in the Conclusions. We also test time moments of the vector current-current correlator against values
determined from the b-quark contribution to σðeþe− → hadronsÞ and calculate the b-quark piece of the
hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon,
ab
μ ¼ 0.271ð37Þ × 10−10. Finally we determine the b-quark mass, obtaining in the MS scheme, ¯
m¯ bðm¯ b; nf ¼ 5Þ ¼ 4.196ð23Þ GeV, the most accurate result from lattice QCD to date
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