15,459 research outputs found
The Spectrum from Lattice NRQCD
I review recent results for heavy-heavy spectroscopy using Lattice NRQCD. The
NRQCD collaboration reports that spin-independent splittings for the
are scaling for a sensible range of values in the quenched
approximation. Spin-dependent splittings are not, if the scale is set by
spin-independent splittings. Results which include higher order spin-dependent
relativistic and discretisation corrections show differences from previous
(NRQCD collaboration) results without these. As expected, the differences are
small for but rather large for charmonium. New results from the
SESAM collaboration for spectroscopy on configurations with Wilson
dynamical fermions show good agreement with previous results on HEMCGC
configurations with staggered dynamical fermions.Comment: 10 pages, Latex. 10 figures, 7 in postscript. Review for Tsukuba
worksho
A review of heavy-heavy spectroscopy
Calculations of the heavy-heavy spectrum present a good opportunity for
precision tests of QCD using lattice techniques. All methods make use of a
non-relativistic expansion of the action and its systematic improvement to
remove lattice artefacts. There was convincing demonstration this year that
these methods work and that the associated perturbation theory is well-behaved.
Comparison to experimental results yields an accurate value for the lattice
spacing, a, a key result in the determination of \alpha_{s}, and (for the first
time this year) the mass of the b quark (4.7(1) GeV).Comment: talk at Lattice'93, Dallas. 6 pages of latex espcrc2.sty needed and
figures on reques
Latest Results from Heavy Quark Simulations
The status of b-bbar and c-cbar calculations, numerical and analytic, are
reviewed. The extraction of alpha_s and quark masses from spectrum calculations
is discussed. The NRQCD and Improved Heavy Wilson formulations of heavy quarks
are compared, and recent calculations using a Heavy Staggered formulation are
discussed.Comment: 15 pages, latex, 9 postscript figures, self-unpacking uuencoded
compressed file, requires espcrc2.sty (included) and epsf.sty. Contribution
to Lattice '9
Heavy Meson Spectroscopy at Beta=6.0
We present results of a quenched calculation of the heavy-light and
quarkonium spectrum using the tadpole improved clover action. We resolve
completely the triplet chi P-states in quarkonium systems, and obtain evidence
for fine structure of the heavy-light P-states. Approximate scaling of the
hyperfine splittings is observed, producing results that are significantly
below experiment.Comment: Contribution to Lattice 97 proceedings: 3 pages, 7 postscript
figures, LaTeX2e, uses espcrc2.st
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 , where is the dynamical strange quark mass and
is the common mass of the and 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.Comment: 10 pages, 17 figures (16 in color), Lattice2003(plenary), Plenary
talk presented at Lattice 2003, Tsukuba, Japan, July 15-19. Also presented at
Lattice Hadron Physics workshop, Cairns, Australia, July 22-30, 200
A precise determination of the Bc mass from dynamical lattice QCD
We perform a precise calculation of the mass of the B_c meson using
unquenched configurations from the MILC collaboration including 2+1 flavours of
improved staggered quarks. Lattice NRQCD and the Fermilab formalism are used to
describe the b and c quarks respectively. We find the mass of the B_c meson to
be 6.304(16) GeVComment: Talk presented at Lattice2004(heavy), Fermilab, June 21-26. 3 pages,
2 figure
Quarkonium spin structure in lattice NRQCD
Numerical simulations of the quarkonium spin splittings are done in the
framework of lattice nonrelativistic quantum chromodynamics (NRQCD). At leading
order in the velocity expansion the spin splittings are of , where
is the renormalized quark mass and is the mean squared quark
velocity. A systematic analysis is done of all next-to-leading order
corrections. This includes the addition of relativistic
interactions, and the removal of discretization errors in the
leading-order interactions. Simulations are done for both S- and P-wave mesons,
with a variety of heavy quark actions and over a wide range of lattice
spacings. Two prescriptions for the tadpole improvement of the action are also
studied in detail: one using the measured value of the average plaquette, the
other using the mean link measured in Landau gauge. Next-to-leading order
interactions result in a very large reduction in the charmonium splittings,
down by about 60% from their values at leading order. There are further
indications that the velocity expansion may be poorly convergent for
charmonium. Prelimary results show a small correction to the hyperfine
splitting in the Upsilon system.Comment: 16 pages, REVTEX v3.1, 5 postscript figures include
Non-Perturbative Improvement of the Anisotropic Wilson QCD Action
We describe the first steps in the extension of the Symanzik O()
improvement program for Wilson-type quark actions to anisotropic lattices, with
a temporal lattice spacing smaller than the spatial one. This provides a fully
relativistic and computationally efficient framework for the study of heavy
quarks. We illustrate our method with accurate results for the quenched
charmonium spectrum.Comment: LATTICE98(improvement), 3 pages, 4 figure
Lattice QCD on Small Computers
We demonstrate that lattice QCD calculations can be made -- times
faster by using very coarse lattices. To obtain accurate results, we replace
the standard lattice actions by perturbatively-improved actions with
tadpole-improved correction terms that remove the leading errors due to the
lattice. To illustrate the power of this approach, we calculate the
static-quark potential, and the charmonium spectrum and wavefunctions using a
desktop computer. We obtain accurate results that are independent of the
lattice spacing and agree well with experiment.Comment: 15 pages, 3 figs incl as LaTex pictures Minor additions to tables and
tex
Tadpole renormalization and relativistic corrections in lattice NRQCD
We make a comparison of two tadpole renormalization schemes in the context of
the quarkonium hyperfine splittings in lattice NRQCD. Improved gauge-field and
NRQCD actions are analyzed using the mean-link in Landau gauge, and
using the fourth root of the average plaquette . Simulations are done
for , , and systems. The hyperfine splittings are
computed both at leading and at next-to-leading order in the relativistic
expansion. Results are obtained at lattice spacings in the range of about
0.14~fm to 0.38~fm. A number of features emerge, all of which favor tadpole
renormalization using . This includes much better scaling behavior of
the hyperfine splittings in the three quarkonium systems when is
used. We also find that relativistic corrections to the spin splittings are
smaller when is used, particularly for the and
systems. We also see signs of a breakdown in the NRQCD expansion when the bare
quark mass falls below about one in lattice units. Simulations with
also appear to be better behaved in this context: the bare quark masses turn
out to be larger when is used, compared to when is used on
lattices with comparable spacings. These results also demonstrate the need to
go beyond tree-level tadpole improvement for precision simulations.Comment: 14 pages, 7 figures (minor changes to some phraseology and
references
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