206 research outputs found
Irreducible pionic effects in nucleon-deuteron scattering below 20 MeV
The consequences of a recently introduced irreducible pionic effect in low
energy nucleon-deuteron scattering are analyzed. Differential cross-sections,
nucleon (vector) and deuteron (vector and tensor) analyzing powers, and four
different polarization transfer coefficients have been considered. This
3NF-like effect is generated by the pion-exchange diagram in presence of a
two-nucleon correlation and is partially cancelled by meson-retardation
contributions. Indications are provided that such type of effects are capable
to selectively increase the vector (nucleon and deuteron) analyzing powers,
while in the considered energy range they are almost negligible on the
differential cross sections. These indications, observed with different
realistic nucleon-nucleon interactions, provide additional evidences that such
3NF-like effects have indeed the potential to solve the puzzle of the vector
analyzing powers. Smaller but non negligible effects are observed for the other
spin observables. In some cases, we find that the modifications introduced by
such pionic effects on these spin observables (other than the vector analyzing
powers) are significant and interesting and could be observed by experiments.Comment: 33 pages, 17 figures, 3 Tables, RevTe
Comparison of triton bound state properties using different separable representations of realistic potentials
The quality of two different separable expansion methods ({\sl W} matrix and
Ernst-Shakin-Thaler) is investigated. We compare the triton binding energies
and components of the triton wave functions obtained in this way with the
results of a direct two-dimensional treatment. The Paris, Bonn {\sl A} and Bonn
{\sl B} potentials are employed as underlying two-body interactions, their
total angular momenta being incorporated up to . It is found that the
most accurate results based on the Ernst-Shakin-Thaler method agree within 1.5%
or better with the two-dimensional calculations, whereas the results for the
{\sl W}-matrix representation are less accurate.Comment: 27 pages, 6 postscript figures included, uses psfi
Spin observables for pion production from pd collisions
We have calculated the proton analyzing power A_{y0} of the pion-production
reaction from pd collisions for one energy close to threshold and for another
in the region of the -resonance. A fair reproduction of the
experimental data could be obtained in both cases with a model which includes
isoscalar and isovector rescatterings in s waves, as well as the p-wave
rescattering mechanisms mediated by the and vertices.
For the analyzing power at threshold we found that the initial-state
interaction (ISI) is also quite important.Comment: Talk at XVIth International Conference on Few-Body Problems in
Physics, Taipei, Taiwan, March 6-10 2000. 3 pages, latex, 2 figures -- To
appear in Nuclear Physics A -- fleqn.sty and espcrc1.sty require
Three-nucleon portrait with pion
We report on recent results obtained by the above collaboration on the
collision processes involving three nucleons, where we pay particular attention
on the dynamical role of the pion. After discussing the case at intermediate
energies, where real pions can be produced and detected, we have considered the
case at lower energies, where the pions being exchanged are virtual. The study
has revealed the presence of some new pion-exchange mechanisms, which leads to
a new three-nucleon force of tensor structure. Recently, the effect of this
tensor three-nucleon force to the spin observables for neutron-deuteron
scattering at low energy has been analyzed, and will be briefly reviewed.Comment: To appear in the Proceedings of 8th Convegno su Problemi di Fisica
Nucleare Teorica (Cortona 2000), Cortona, Italy, 18-21 Oct 2000. 8 pages,
uses ws-p8-50x6-00.cl
Comparison of triton bound state properties using different separable representations of realistic potentials
The quality of two different separable expansion methods ({\sl W} matrix and Ernst-Shakin-Thaler) is investigated. We compare the triton binding energies and components of the triton wave functions obtained in this way with the results of a direct two-dimensional treatment. The Paris, Bonn {\sl A} and Bonn total angular momenta being incorporated up to . It is found that the most accurate results based on the Ernst-Shakin-Thaler method agree within 1.5% or better with the two-dimensional calculations, whereas the results for th
Radiative capture of protons by deuterons
The differential cross section for radiative capture of protons by deuterons
is calculated using different realistic NN interactions. We compare our results
with the available experimental data below . Excellent agreement
is found when taking into account meson exchange currents, dipole and
quadrupole contributions, and the full initial state interaction. There is only
a small difference between the magnitudes of the cross sections for the
different potentials considered. The angular distributions, however, are
practically potential independent.Comment: 4 pages (twocolumn), 4 postscript figures included, submitted for
publication, revised versio
Photonuclear Reactions of Three-Nucleon Systems
We discuss the available data for the differential and the total cross
section for the photodisintegration of He and H and the corresponding
inverse reactions below MeV by comparing with our calculations
using realistic interactions. The theoretical results agree within the
errorbars with the data for the total cross sections. Excellent agreement is
achieved for the angular distribution in case of He, whereas for H a
discrepancy between theory and experiment is found.Comment: 11 pages (twocolumn), 12 postscript figures included, uses psfig,
RevTe
Isoscalar off-shell effects in threshold pion production from pd collisions
We test the presence of pion-nucleon isoscalar off-shell effects in the
reaction around the threshold region. We find that these
effects significantly modify the production cross section and that they may
provide the missing strength needed to reproduce the data at threshold.Comment: 6 pages, REVTeX, twocolumn, including 3 figures (Postscript), uses
psfig, updated and extended versio
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