415 research outputs found
On the and as Bound States and Approximate Nambu-Goldstone Bosons
We reconsider the two different facets of and mesons as
bound states and approximate Nambu-Goldstone bosons. We address several topics,
including masses, mass splittings between and and between and
, meson wavefunctions, charge radii, and the wavefunction overlap.Comment: 15 pages, late
Di-electron and two-photon widths in charmonium
The vector and pseudoscalar decay constants are calculated in the framework
of the Field Correlator Method. Di-electron widths:
keV, keV,
keV, in good agreement with experiment, are obtained with the same coupling,
, in QCD radiative corrections. We show that the larger
is needed to reach agreement with experiment for
keV, keV, keV, and
also for keV,
keV. Meanwhile even larger gives rise to good description of
keV, keV, and
provides correct ratio of the branching fractions: Comment: 8 pages, no figure
Leptonic widths of high excitations in heavy quarkonia
Agreement with the measured electronic widths of the ,
, and resonances is shown to be reached if two
effects are taken into account: a flattening of the confining potential at
large distances and a total screening of the gluon-exchange interaction at
r\ga 1.2 fm. The leptonic widths of the unobserved and
resonances: keV and
keV are predicted.Comment: 11 pages revtex
Vector Meson Production at HERA
We show that the lowest-order QCD calculation in a simple model of elastic
vector-meson production does reproduce correctly the ratios of cross sections
for rho, phi and J/psi, both in photoproduction and in high-Q2 quasi-elastic
scattering. The dependence of the slopes on the mass of the vector meson is
reproduced as well. We examine the lower-energy data, and find that the energy
dependence of the cross section does not depend on Q2, but may depend on the
vector-meson mass.Comment: 12 pages, Latex, 6 figures. Shortened version of the previous paper,
which also includes a clearer criticism of the work by Martin, Ryskin and
Teubner, hep-ph/960944
Which factors prognosticate rotational instability following lumbar laminectomy?
Purpose: Reduced strength and stiffness of lumbar spinal motion segments following laminectomy may lead to instability. Factors that predict shear biomechanical properties of the lumbar spine were previously published. The purpose of the present study was to predict spinal torsion biomechanical properties with and without laminectomy from a total of 21 imaging parameters. Method: Radiographs and MRI of ten human cadaveric lumbar spines (mean age 75.5, range 59-88 years) were obtained to quantify geometry and degeneration of the motion segments. Additionally, dual X-ray absorptiometry (DXA) scans were performed to measure bone mineral content and density. Facet-sparing lumbar laminectomy was performed either on L2 or L4. Spinal motion segments were dissected (L2-L3 and L4-L5) and tested in torsion, under 1,600 N axial compression. Torsion moment to failure (TMF), early torsion stiffness (ETS, at 20-40 % TMF) and late torsion stiffness (LTS, at 60-80 % TMF) were determined and bivariate correlations with all parameters were established. For dichotomized parameters, independent-sample t tests were used. Results: Univariate analyses showed that a range of geometric characteristics and disc and bone quality parameters were associated with torsion biomechanical properties of lumbar segments. Multivariate models showed that ETS, LTS and TMF could be predicted for segments without laminectomy (
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