191 research outputs found
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
Particle-unstable light nuclei with a Sturmian approach that preserves the Pauli principle
Sturmian theory for nucleon-nucleus scattering is discussed in the presence
of all the phenomenological ingredients necessary for the description of
weakly-bound (or particle-unstable) light nuclear systems. Currently, we use a
macroscopic potential model of collective nature. The analysis shows that the
couplings to low-energy collective-core excitations are fundamental but they
are physically meaningful only if the constraints introduced by the Pauli
principle are taken into account. The formalism leads one to discuss a new
concept, Pauli hindrance, which appears to be important to understand the
structure of weakly-bound and unbound systems.Comment: 5 pages, 2 figures, 1 table, contribution to proceedings of "18th
International IUPAP Conference on Few-Body Problems in Physics," Santos,
Brazil, August 21-26, 200
Complex Conjugate Pairs in Stationary Sturmians
Sturmian eigenstates specified by stationary scattering boundary conditions
are particularly useful in contexts such as forming simple separable two
nucleon t matrices, and are determined via solution of generalised eigenvalue
equation using real and symmetric matrices. In general, the spectrum of such an
equation may contain complex eigenvalues. But to each complex eigenvalue there
is a corresponding conjugate partner. In studies using realistic
nucleon--nucleon potentials, and in certain positive energy intervals, these
complex conjugated pairs indeed appear in the Sturmian spectrum. However, as we
demonstrate herein, it is possible to recombine the complex conjugate pairs and
corresponding states into a new, sign--definite pair of real quantities with
which to effect separable expansions of the (real) nucleon--nucleon reactance
matrices.Comment: (REVTEX) 8 Pages, Padova DFPD 93/TH/78 and University of Melbourn
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