116 research outputs found
Chiral two-pion exchange and proton-proton partial-wave analysis
The chiral two-pion exchange component of the long-range pp interaction is
studied in an energy-dependent partial-wave analysis. We demonstrate its
presence and importance, and determine the chiral parameters c_i (i=1,3,4). The
values agree well with those obtained from pion-nucleon amplitudes.Comment: 13 pages, no figure
On the pion-nucleon coupling constant
In view of persisting misunderstanding about the determination of the
pion-nucleon coupling constants in the Nijmegen multienergy partial-wave
analyses of pp, np, and pbar-p scattering data, we present additional
information which may clarify several points of discussion. We comment on
several recent papers addressing the issue of the pion-nucleon coupling
constant and criticizing the Nijmegen analyses.Comment: 19 pages, Nijmegen preprint THEF-NYM-92-0
Angle-dependent normalization of neutron-proton differential cross sections
Systematic errors in the database of differential cross sections below
350 MeV are studied. By applying angle-dependent normalizations with the help
of the energy-dependent Nijmegen partial-wave analysis PWA93 the
-values of some seriously flawed data sets can be reduced significantly
at the expense of a few degrees of freedom. It turns out that in these special
cases the renormalized data sets can be made statistically acceptable such that
they do not have to be discarded any longer in partial-wave analyses of the
two-nucleon scattering data.Comment: 11 pages, 1 figure; expanded versio
Baryon-Baryon Interactions
After a short survey of some topics of interest in the study of baryon-baryon
scattering, the recent Nijmegen energy dependent partial wave analysis (PWA) of
the nucleon-nucleon data is reviewed. In this PWA the energy range for both pp
and np is now 0 < Tlab < 350 MeV and a chi^2_{d.o.f.}=1.08 was reached. The
implications for the pion-nucleon coupling constants are discussed. Comments
are made with respect to recent discussions around this coupling constant in
the literature. In the second part, we briefly sketch the picture of the baryon
in several, more or less QCD-based, quark-models that have been rather
prominent in the literature. Inspired by these pictures we constructed a new
soft-core model for the nucleon-nucleon interaction and present the first
results of this model in a chi^2 -fit to the new multi-energy Nijmegen PWA.
With this new model we succeeded in narrowing the gap between theory and
experiment at low energies. For the energies Tlab = 25-320 MeV we reached a
record low chi^2_{p.d.p.} = 1.16. We finish the paper with some conclusions and
an outlook describing the extension of the new model to baryon-baryon
scattering.Comment: 12 pages LaTeX and one postscript figure included. Invited talk
presented at the XIVth European Conference of Few-Body Problems in Physics,
Amsterdam, August 23-28, 199
pi-NN Coupling Constants from NN Elastic Data between 210 and 800 Mev
High partial waves for and elastic scattering are examined
critically from 210 to 800 MeV. Non-OPE contributions are compared with
predictions from theory. There are some discrepancies, but sufficient agreement
that values of the coupling constants for exchange
and for charged exchange can be derived. Results are and , where the first error is statistical and the
second is an estimate of the likely systematic error, arising mostly from
uncertainties in the normalisation of total cross sections and
.Comment: 21 pages of LaTeX, UI-NTH-940
Multipair contributions to the spin response of nuclear matter
We analyse the effect of non-central forces on the magnetic susceptibility of
degenerate Fermi systems. These include the presence of contributions from
transitions to states containing more than one quasiparticle-quasihole pair,
which cannot be calculated within the framework of Landau Fermi-liquid theory,
and renormalization of the quasiparticle magnetic moment, as well as explicit
non-central contributions to the quasiparticle interaction. Consequently, the
relationship between the Landau parameters and the magnetic susceptibility for
Fermi systems with non-central forces is considerably more complicated than for
systems with central forces. We use sum-rule arguments to place a lower bound
on the contribution to the static susceptibility coming from transitions to
multipair states
Quantum Monte Carlo Calculations of Nuclei
The energies of , , and ground states, the
and scattering states of , the
ground states of , , and and the and
excited states of have been accurately calculated with the Green's
function Monte Carlo method using realistic models of two- and three-nucleon
interactions. The splitting of the isospin and
isospin , multiplets is also studied. The observed
energies and radii are generally well reproduced, however, some definite
differences between theory and experiment can be identified.Comment: 12 pages, 1 figur
proton-deuteron elastic scattering above the deuteron breakup
The complex Kohn variational principle and the (correlated) hyperspherical
harmonics method are applied to study the proton-deuteron elastic scattering at
energies above the deuteron breakup threshold. Results for the elastic cross
section and various elastic polarization observables have been obtained by
fully taking into account the long-range effect of the Coulomb interaction and
using a realistic nucleon-nucleon interaction model. Detailed comparison
between the theoretical predictions and the accurate and abundant
proton-deuteron experimental data can now be performed.Comment: 6 pages, 2 figure
Phenomenological Lambda-Nuclear Interactions
Variational Monte Carlo calculations for (ground and
excited states) and are performed to decipher information on
-nuclear interactions. Appropriate operatorial nuclear and
-nuclear correlations have been incorporated to minimize the
expectation values of the energies. We use the Argonne two-body
NN along with the Urbana IX three-body NNN interactions. The study demonstrates
that a large part of the splitting energy in () is
due to the three-body NN forces. hypernucleus is
analyzed using the {\it s}-shell results. binding to nuclear matter
is calculated within the variational framework using the
Fermi-Hypernetted-Chain technique. There is a need to correctly incorporate the
three-body NN correlations for binding to nuclear matter.Comment: 18 pages (TeX), 2 figure
Role of heavy-meson exchange in pion production near threshold
Recent calculations of -wave pion production have severely underestimated
the accurately known \ total cross section near
threshold. In these calculations, only the single-nucleon axial-charge operator
is considered. We have calculated, in addition to the one-body term, the
two-body contributions to this reaction that arise from the exchange of mesons.
We find that the inclusion of the scalar -meson exchange current (and
lesser contributions from other mesons) increases the cross section by about a
factor of five, and leads to excellent agreement with the data. The results are
neither very sensitive to changes in the distorting potential that generates
the wave function, nor to different choices for the meson-nucleon form
factors. We argue that \ data provide direct
experimental evidence for meson-exchange contributions to the axial current.Comment: 28 Pages, IU-NTC #93-0
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