100 research outputs found
Where do perturbative and non-perturbative QCD meet?
We computed the static potential and Wilson loops to in
perturbation theory for different lattice quark and gluon actions. In general,
we find short distance lattice data to be well described by ``boosted
perturbation theory''. For Wilson-type fermions at present-day quark masses and
lattice spacings agreement within 10% between measured ``-shifts'' and
those predicted by perturbation theory is found. We comment on prospects for a
determination of the real world QCD running coupling.Comment: 3 pages, 4 figures, Talk at Lattice 2001 in renormalisation and
improvement sessio
A nonperturbative determination of cA
We describe a non-perturbative determination of using correlators
containing the axial-vector and pseudoscalar currents at zero and non-zero
momentum. We apply the method of Bhattacharya et al to extract from the
requirement that the ratio of appropriate correlators for the PCAC relation
becomes independent of time in the excited state region. We find that the
result depends strongly on the order of the derivatives used in the PCAC
relation. We also find that, using the lowest order derivatives, we cannot get
a consistent value of between zero and non-zero momentum cases. The
values that we obtain as we improve the derivatives are consistent and decrease
in magnitude heading towards the perturbative result.Comment: Lattice 2000 (Improvment and Renormalisation) 5 pages Latex, 7
postscript figure
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
Computation of the Heavy-Light Decay Constant using Non-relativistic Lattice QCD
We report results on a lattice calculation of the heavy-light meson decay
constant employing the non-relativistic QCD approach for heavy quark and Wilson
action for light quark. Simulations are carried out at on a
lattice. Signal to noise ratio for the ground state is
significantly improved compared to simulations in the static approximation,
enabling us to extract the decay constant reliably. We compute the heavy-light
decay constant for several values of heavy quark mass and estimate the
magnitude of the deviation from the heavy mass scaling law . For the meson we find MeV, while
an extrapolation to the static limit yields = MeV.Comment: 34 pages in LaTeX including 10 figures using epsf.sty,
uuencoded-gziped-shar format, HUPD-940
A study of the quenched bc mass spectrum at beta=6.2
We present an analysis of the mass spectrum of heavy quarkonia with
non-degenerate quark masses. The heavier (bottom) valence quark is treated in a
non-relativistic fashion and the other (charm) is a relativistic Wilson-like
quark using the improved SW action. Such states provide and interesting probe
between the relativistic B meson states and the non-relativistic bottomonium
states.Comment: 4 pages LaTeX, 4 postscript figures. requires espcrc2.sty and
epsf.sty. To be published in the proceedings of Lattice 97, Edinburgh,
Scotlan
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
Estimate of the hadronic vacuum polarization disconnected contribution to the anomalous magnetic moment of the muon from lattice QCD
The quark-line disconnected diagram is a potentially important ingredient in lattice QCD calculations of the hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon. It is also a notoriously difficult one to evaluate. Here, for the first time, we give an estimate of this contribution based on lattice QCD results that have a statistically significant signal, albeit at one value of the lattice spacing and an unphysically heavy value of the u/d quark mass. We use HPQCDâs method of determining the anomalous magnetic moment by reconstructing the Adler function from time moments of the current-current correlator at zero spatial momentum. Our results lead to a total (including u, d and s quarks) quark-line disconnected contribution to aÎŒ of â0.15% of the u/d hadronic vacuum polarization contribution with an uncertainty which is 1% of that contribution
Constrained fitting of three-point functions
We determine matrix elements for semileptonic decay. The use of the
constrained fitting method and multiple smearings for both two- and three-point
correlators allows an improved calculation of the form factors.Comment: Talk given at Lattice2001(heavyquark), 3 pages, 4 figure
Renormalising vector currents in lattice QCD using momentum-subtraction schemes
No abstract available
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
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