329 research outputs found
Fitting Correlated Hadron Mass Spectrum Data
We discuss fitting hadronic Green functions versus time to extract mass
values in quenched lattice QCD. These data are themselves strongly correlated
in . With only a limited number of data samples, the method of minimising
correlated is unreliable. We explore several methods of modelling the
correlations among the data set by a few parameters which then give a stable
and sensible fit even if the data sample is small. In particular these models
give a reliable estimate of the goodness of fit.Comment: 14 pages, Latex text, followed by 3 postscript figures in
self-unpacking file. Also available at
ftp://suna.amtp.liv.ac.uk/pub/cmi/corfit
Efficient Hadronic Operators in Lattice Gauge Theory
We study operators to create hadronic states made of light quarks in quenched
lattice gauge theory. We construct non-local gauge-invariant operators which
provide information about the spatial extent of the ground state and excited
states. The efficiency of the operators is shown by looking at the wave
function of the first excited state, which has a node as a function of the
spatial extent of the operator. This allows one to obtain an uncontaminated
ground state for hadrons.Comment: 18 pages, Latex text, followed by 11 postscript figures in
self-unpacking file. Also available at
ftp://suna.amtp.liv.ac.uk/pub/cmi/wavefn
Quenched Hadron Spectrum and Decay Constants on the lattice
In this talk we present the results obtained from a study of
(quenched) lattice configurations from the APE collaboration, at
, using both the Wilson and the SW-Clover fermion action.
We determine the light hadronic spectrum and the meson decay constants. For the
light-light systems we find an agreement with the experimental data of for mesonic masses and for baryonic masses and pseudoscalar
decay constants; a larger deviation is present for the vector decay constants.
For the heavy-light decay constants we find , in good agreement with previous estimates.Comment: 8 pages, latex, Talk given at XXV ITEP Winter School of Physics,
Moscow - Russia, 18-27 Feb 199
Chiral and Continuum Extrapolation of Partially-Quenched Hadron Masses
Using the finite-range regularisation (FRR) of chiral effective field theory,
the chiral extrapolation formula for the vector meson mass is derived for the
case of partially-quenched QCD. We re-analyse the dynamical fermion QCD data
for the vector meson mass from the CP-PACS collaboration. A global fit,
including finite lattice spacing effects, of all 16 of their ensembles is
performed. We study the FRR method together with a naive polynomial approach
and find excellent agreement ~1% with the experimental value of M_rho from the
former approach. These results are extended to the case of the nucleon mass.Comment: 6 pages, Contribution to Lattice2005, PoS styl
Chiral and Continuum Extrapolation of Partially-Quenched Lattice Results
The vector meson mass is extracted from a large sample of partially quenched,
two-flavor lattice QCD simulations. For the first time, discretisation,
finite-volume and partial quenching artefacts are treated in a unified
framework which is consistent with the low-energy behaviour of QCD. This
analysis incorporates the leading infrared behaviour dictated by chiral
effective field theory. As the two-pion decay channel cannot be described by a
low-energy expansion alone, a highly-constrained model for the decay channel of
the rho-meson is introduced. The latter is essential for extrapolating lattice
results from the quark-mass regime where the rho is observed to be a physical
bound state.Comment: 9 pages, 3 figures; revised version appearing in PL
EoS of finite density QCD with Wilson fermions by Multi-Parameter Reweighting and Taylor expansion
The equation of state (EoS), quark number density and susceptibility at
nonzero quark chemical potential are studied in lattice QCD simulations
with a clover-improved Wilson fermion of 2-flavors and RG-improved gauge
action. To access nonzero , we employ two methods : a multi-parameter
reweighting (MPR) in and and Taylor expansion in . The use
of a reduction formula for the Wilson fermion determinant enables to study the
reweighting factor in MPR explicitly and heigher-order coefficients in Taylor
expansion free from errors of noise method, although calculations are limited
to small lattice size. As a consequence, we can study the reliability of the
thermodynamical quantities through the consistency of the two methods, each of
which has different origin of the application limit.
The thermodynamical quantities are obtained from simulations on a lattice with an intermediate quark mass(. The MPR
and Taylor expansion are consistent for the EoS and number density up to
and for the number susceptibility up to . This
implies within a given statistics that the overlap problem for the MPR and
truncation error for the Taylor expansion method are negligible in these
regions.
In order to make MPR methods work, the fluctuation of the reweighting factor
should be small. We derive the equation of the reweighting line where the
fluctuation is small, and show that the equation of the reweighting line is
consistent with the fluctuation minimum condition.Comment: 20 pages, 11 figures. Accepted to JHEP. Discussions are added.
Figures for Taylor coefficients (Fig. 7) are modifie
The charm quark mass with dynamical fermions
We compute the charm quark mass in lattice QCD and compare different
formulations of the heavy quark, and quenched data to that with dynamical sea
quarks. We take the continuum limit of the quenched data by extrapolating from
three different lattice spacings, and compare to data with two flavours of
dynamical sea quarks with a mass around the strange at the coarsest lattice
spacing. Both the FNAL and ALPHA formalism are used. We find the different
heavy quark formulations have the same continuum limit in the quenched
approximation, and limited evidence that this approximation overestimates the
charm quark mass.Comment: Lattice2004(heavy) 3 pages, 2 figure
Heavy Quark Spectroscopy and Matrix Elements: A Lattice Study using the Static Approximation
We present results of a lattice analysis of the parameter, , the
decay constant , and several mass splittings using the static
approximation. Results were obtained for 60 quenched gauge configurations
computed at on a lattice size of . Light quark
propagators were calculated using the -improved Sheikholeslami-Wohlert
action. We find \Bbstat(m_b) = 0.69\er{3}{4} {\rm(stat)}\er{2}{1}
{\rm(syst)}, corresponding to \Bbstat = 1.02\er{5}{6}\er{3}{2}, and \fbstat
= 266\err{18}{20}\err{28}{27} \mev, f_{B_s}^2 B_{B_s}/f_B^2 B_B =
1.34\er{9}{8}\er{5}{3}, where a variational fitting technique was used to
extract \fbstat. For the mass splittings we obtain M_{B_s}-M_{B_d} =
87\err{15}{12}\err{6}{12} \mev, M_{\Lambda_b}-M_{B_d} =
420\errr{100}{90}\err{30}{30} \mev and M_{B^*}^2-M_B^2 =
0.281\err{15}{16}\err{40}{37} \gev^2. We compare different smearing techniques
intended to improve the signal/noise ratio. From a detailed assessment of
systematic effects we conclude that the main systematic uncertainties are
associated with the renormalisation constants relating a lattice matrix element
to its continuum counterpart. The dependence of our findings on lattice
artefacts is to be investigated in the future.Comment: 40 pages, uuencoded compressed tar file, containing one LaTeX file
and 14 postscript files (to be included with epsf). Minor change in the value
of the B parameter. Contains corrected value for the B*-B mass splitting.
Version accepted for publication in Phys. Rev.
Unified chiral analysis of the vector meson spectrum from lattice QCD
The chiral extrapolation of the vector meson mass calculated in
partially-quenched lattice simulations is investigated. The leading one-loop
corrections to the vector meson mass are derived for partially-quenched QCD. A
large sample of lattice results from the CP-PACS Collaboration is analysed,
with explicit corrections for finite lattice spacing artifacts. To incorporate
the effect of the opening decay channel as the chiral limit is approached, the
extrapolation is studied using a necessary phenomenological extension of chiral
effective field theory. This chiral analysis also provides a quantitative
estimate of the leading finite volume corrections. It is found that the
discretisation, finite-volume and partial quenching effects can all be very
well described in this framework, producing an extrapolated value of M_\rho in
excellent agreement with experiment. This procedure is also compared with
extrapolations based on polynomial forms, where the results are much less
enlightening.Comment: 30 pages, 13 fig
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