1,505 research outputs found
Precision determination of the pi-N scattering lengths and the charged pi-NN coupling constant
We critically evaluate the isovector GMO sumrule for the charged
coupling constant using recent precision data from p and d atoms
and with careful attention to systematic errors. From the d scattering
length we deduce the pion-proton scattering lengths (statistic) (systematic))~ and . From this a direct evaluation gives (statistic)(systematic) or .Comment: 4 pages, 1 figure, latex and postscript; invited talk at PANIC99; to
appear in Nucl. Phys. A; changed notation: g^2 and f^2 replaced by
conventional g^2/4\pi and f^2/4\p
Chiral Dynamics of Deeply Bound Pionic Atoms
We present and discuss a systematic calculation, based on two-loop chiral
perturbation theory, of the pion-nuclear s-wave optical potential. A proper
treatment of the explicit energy dependence of the off-shell pion self-energy
together with (electromagnetic) gauge invariance of the Klein-Gordon equation
turns out to be crucial. Accurate data for the binding energies and widths of
the 1s and 2p levels in pionic ^{205}Pb and ^{207}Pb are well reproduced, and
the notorious "missing repulsion" in the pion-nuclear s-wave optical potential
is accounted for. The connection with the in-medium change of the pion decay
constant is clarified.Comment: preprint ECT*-02-16, 4 pages, 3 figure
How Precisely can we Determine the \piNN Coupling Constant from the Isovector GMO Sum Rule?
The isovector GMO sum rule for zero energy forward pion-nucleon scattering iscritically studied to obtain the charged pion-nucleon coupling constant usingthe precise negatively charged pion-proton and pion-deuteron scattering lengthsdeduced recently from pionic atom experiments. This direct determination leadsto a pseudoscalar charged pion-nucleon coupling constant of 14.23 +- 0.09(statistic) +- 0.17 (systematic). We obtain also accurate values for thepion-nucleon scattering lengths
How precisely can we determine the pion-nucleon coupling constant from the isovector GMO sum rule?
The isovector GMO sum rule for zero energy forward pion-nucleon scattering is
critically studied to obtain the charged pion-nucleon coupling constant using
the precise negatively charged pion-proton and pion-deuteron scattering lengths
deduced recently from pionic atom experiments. This direct determination leads
to a pseudoscalar charged pion-nucleon coupling constant of 14.23 +- 0.09
(statistic) +- 0.17 (systematic). We obtain also accurate values for the
pion-nucleon scattering lengths.Comment: Talk given at the Eighth International Symposium on Meson-Nucleon
Physics and the Structure of the Nucleon, Zuoz, Switzerland, August 15-21,
1999, 5 pages, 2 figures, file menu.cls include
In-Place Stabilization of Waste Phosphatic Clays Using Lime Columns
This paper will present the results of a laboratory testing program and field implementation of the lime column stabilization technique to waste phosphatic clays. Results show increases in clay shear strength by 2 to 3 orders of magnitude and reduce the time of primary consolidation by 1 to 2 orders of magnitude
Regge phenomenology of pion photoproduction off the nucleon at forward angles
We present a Regge model for pion photoproduction which is basically free of
parameters within the framework of the s-channel helicity amplitude. We use
coupling constants of all exchanged mesons determined from empirical decay
widths or from the SU(3) relations together with consistency check with
existing estimates that are widely accepted in other reaction processes. Cross
sections and spin polarization asymmetries at various photon energies are
analyzed and results are obtained in better agreement with experimental data
without referring to any fitting procedure.Comment: 19 pages, 20 figures, two column, revtex
Meson-induced correlations of nucleons in nuclear Compton scattering
The non-resonant (seagull) contribution to the nuclear Compton amplitude at
low energies is strongly influenced by nucleon correlations arising from meson
exchange. We study this problem in a modified Fermi gas model, where nuclear
correlation functions are obtained with the help of perturbation theory. The
dependence of the mesonic seagull amplitude on the nuclear radius is
investigated and the influence of a realistic nuclear density on this amplitude
is dicussed. We found that different form factors appear for the static part
(proportional to the enhancement constant ) of the mesonic seagull
amplitude and for the parts, which contain the contribution from
electromagnetic polarizabilities.Comment: 15 pages, Latex, epsf.sty, 9 eps figures
Precise strength of the NN coupling constant
We report here a preliminary value for the piNN coupling constant deduced from the GMO sumrule for forward piN scattering. As in our previous determination from np backward differential scattering cross sections we give a critical discussion of the analysis with careful attention not only to the statistical, but also to the systematic uncertainties. Our preliminary evaluation gives (GMO) = 13.99(24)
Hadron attenuation in deep inelastic lepton-nucleus scattering
We present a detailed theoretical investigation of hadron attenuation in deep
inelastic scattering (DIS) off complex nuclei in the kinematic regime of the
HERMES experiment. The analysis is carried out in the framework of a
probabilistic coupled-channel transport model based on the
Boltzmann-Uehling-Uhlenbeck (BUU) equation, which allows for a treatment of the
final-state interactions (FSI) beyond simple absorption mechanisms.
Furthermore, our event-by-event simulations account for the kinematic cuts of
the experiments as well as the geometrical acceptance of the detectors. We
calculate the multiplicity ratios of charged hadrons for various nuclear
targets relative to deuterium as a function of the photon energy nu, the hadron
energy fraction z_h=E_h/nu and the transverse momentum p_T. We also confront
our model results on double-hadron attenuation with recent experimental data.
Separately, we compare the attenuation of identified hadrons (pi^\pm, \pi^0,
K^\pm, p and pbar) on Ne and Kr targets with the data from the HERMES
Collaboration and make predictions for a Xe target. At the end we turn towards
hadron attenuation on Cu nuclei at EMC energies. Our studies demonstrate that
(pre-)hadronic final-state interactions play a dominant role in the kinematic
regime of the HERMES experiment while our present approach overestimates the
attenuation at EMC energies.Comment: 61 pages, 19 figures, version accepted for publication in Phys. Rev.
Polaron Variational Methods In The Particle Representation Of Field Theory : II. Numerical Results For The Propagator
For the scalar Wick-Cutkosky model in the particle representation we perform
a similar variational calculation for the 2-point function as was done by
Feynman for the polaron problem. We employ a quadratic nonlocal trial action
with a retardation function for which several ans\"atze are used. The
variational parameters are determined by minimizing the variational function
and in the most general case the nonlinear variational equations are solved
numerically. We obtain the residue at the pole, study analytically and
numerically the instability of the model at larger coupling constants and
calculate the width of the dressed particle.Comment: 25 pages standard LaTeX, 9 uuencoded postscript figures embedded with
psfig.st
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