44,651 research outputs found
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
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
Precision Charmonium Spectroscopy From Lattice QCD
We present results for Charmonium spectroscopy using Non-Relativistic QCD
(NRQCD). For the NRQCD action the leading order spin-dependent and next to
leading order spin-independent interactions have been included with
tadpole-improved coefficients. We use multi-exponential fits to multiple
correlation functions to extract ground and excited states. Splittings
between the lowest , and states are given and we have accurate
values for the state hyperfine splitting and the fine structure.
Agreement with experiment is good - the remaining systematic errors are
discussed.Comment: 23 pages uuencoded latex file. Contains figures in late
Decoherence-free quantum-information processing using dipole-coupled qubits
We propose a quantum-information processor that consists of decoherence-free
logical qubits encoded into arrays of dipole-coupled qubits. High-fidelity
single-qubit operations are performed deterministically within a
decoherence-free subsystem without leakage via global addressing of bichromatic
laser fields. Two-qubit operations are realized locally with four physical
qubits, and between separated logical qubits using linear optics. We show how
to prepare cluster states using this method. We include all
non-nearest-neighbor effects in our calculations, and we assume the qubits are
not located in the Dicke limit. Although our proposal is general to any system
of dipole-coupled qubits, throughout the paper we use nitrogen-vacancy (NV)
centers in diamond as an experimental context for our theoretical results.Comment: 7 pages, 5 figure
Direct determination of the strange and light quark condensates from full lattice QCD
We determine the strange quark condensate from lattice QCD for the first time and compare its value to that of the light quark and chiral condensates. The results come from a direct calculation of the expectation value of the trace of the quark propagator followed by subtraction of the appropriate perturbative contribution, derived here, to convert the non-normal-ordered mÏÌ
Ï to the MSÌ
scheme at a fixed scale. This is then a well-defined physical ânonperturbativeâ condensate that can be used in the operator product expansion of current-current correlators. The perturbative subtraction is calculated through O(αs) and estimates of higher order terms are included through fitting results at multiple lattice spacing values. The gluon field configurations used are âsecond generationâ ensembles from the MILC collaboration that include 2+1+1 flavors of sea quarks implemented with the highly improved staggered quark action and including u/d sea quarks down to physical masses. Our results are âšsÌ
sâ©MSÌ
(2ââGeV)=-(290(15)ââMeV)3, âšlÌ
lâ©MSÌ
(2ââGeV)=-(283(2)ââMeV)3, where l is a light quark with mass equal to the average of the u and d quarks. The strange to light quark condensate ratio is 1.08(16). The light quark condensate is significantly larger than the chiral condensate in line with expectations from chiral analyses. We discuss the implications of these results for other calculations
Precision Upsilon Spectroscopy from Nonrelativistic Lattice QCD
The spectrum of the Upsilon system is investigated using the Nonrelativistic
Lattice QCD approach to heavy quarks and ignoring light quark vacuum
polarization. We find good agreement with experiment for the Upsilon(1S),
Upsilon(2S), Upsilon(3S) and for the center of mass and fine structure of the
chi_b states. The lattice calculations predict b-bbar D-states with center of
mass at (10.20 +/- 0.07 +/- 0.03)GeV. Fitting procedures aimed at extracting
both ground and excited state energies are developed. We calculate a
nonperturbative dispersion mass for the Upsilon(1S) and compare with
tadpole-improved lattice perturbation theory.Comment: 8 pages, latex, SCRI-94-57, OHSTPY-HEP-T-94-00
The Heavy-Light Spectrum from Lattice NRQCD
We present a lattice investigation of heavy-light mesons in the quenched
approximation, using non-relativistic QCD for the heavy quark and a clover
improved Wilson formulation for the light quark. A comprehensive calculation of
the heavy-light spectrum has been performed for various heavy quark masses
around the . Our results for the splitting agree well with the
experimental value. We find the splitting to be compatible with
experiment, albeit with large error bars. Our splitting is slightly
low, which could be explained as an effect of quenching. For the first time, we
are able to estimate the mass of states at the and compare them with
experiment.Comment: 24 pages, latex, 10 figures in uuencoded compressed postscrip
- âŠ