2,460 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
Meson Dynamics and the resulting "3-Nucleon-Force" diagrams: Results from a simplified test case
A simplified 1D (one-dimensional) model for a generalized 3N system is
considered, as a testing ground for the explicit treatment of the meson
dynamics in this system. We focus attention on the irreducible diagrams
generated by the pion dynamics in the 3N system, and in particular to a new
type of three-nucleon force discussed recently in the literature, and generated
by the one-pion-exchange mechanism in presence of a nucleon-nucleon
correlation. It is found that these new terms in the simplified model have an
approximately 30% effect compared to the standard three-nucleon force terms in
a `Triton' binding energy calculation. It is suggested that this effect should
also not be ignored in realistic calculations.Comment: 4 pages, Contribution to "Mesons and Light Nuclei 2001", Prague 2-6,
200
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
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