5 research outputs found
Final-State Interactions in (e,e'p) Reactions with Polarized Nuclei
The cross section for coincidence, quasielastic proton knock-out by electrons
from a polarized K39 nucleus is computed in DWIA using an optical potential in
describing the wave function of the ejected nucleon. The dependence of the FSI
on the initial polarization angles of the nucleus is analyzed and explained in
a new, semi-classical picture of the reaction in which the nuclear transparency
decreases as a function of the amount of nuclear matter that the proton has to
cross, thus providing a method for obtaining detailed information on its mean
free path in finite nuclei. We propose a procedure to find the best initial
kinematical conditions for minimizing the FSI which will be useful as a guide
for future experiments with polarized nuclei.Comment: 26 pages, 8 Postscript figures, uses epsf.st
Inclusive quasielastic scattering of polarized electrons from polarized nuclei
The inclusive quasielastic response functions that appear in the scattering
of polarized electrons from polarized nuclei are computed and analyzed for
several closed-shell-minus-one nuclei with special attention paid to 39K.
Results are presented using two models for the ejected nucleon --- when
described by a distorted wave in the continuum shell model or by a plane wave
in PWIA with on- and off-shell nucleons. Relativistic effects in kinematics and
in the electromagnetic current have been incorporated throughout. Specifically,
the recently obtained expansion of the electromagnetic current in powers only
of the struck nucleon's momentum is employed for the on-shell current and the
effects of the first-order terms (spin-orbit and convection) are compared with
the zeroth-order (charge and magnetization) contributions. The use of polarized
inclusive quasielastic electron scattering as a tool for determining
near-valence nucleon momentum distributions is discussed.Comment: 51 LaTeX pages, 14 Postscript figure
Relativistic Effects in Electromagnetic Meson-Exchange Currents for One-Particle Emission Reactions
Following recent studies of non-relativistic reductions of the single-nucleon
electromagnetic current operator, here we extend the treatment to include meson
exchange current operators. We focus on one-particle emission electronuclear
reactions. In contrast to the traditional scheme where approximations are made
for the transferred momentum, transferred energy and momenta of the
initial-state struck nucleons, we treat the problem exactly for the transferred
energy and momentum, thus obtaining new current operators which retain
important aspects of relativity not taken into account in the traditional
non-relativistic reductions. We calculate the matrix elements of our current
operators between the Fermi sphere and a particle-hole state for several
choices of kinematics. We present a comparison between our results using
approximate current operators and those obtained using the fully-relativistic
operators, as well as with results obtained using the traditional
non-relativistic current operators.Comment: LaTeX, 31 pages, 7 Postscript figures, to be published in Nucl. Phys.
Meson-exchange contributions to the nuclear charge operator
The role of the meson-exchange current correction to the nuclear charge
operator is studied in electron scattering processes involving the excitation
of medium and heavy nuclei to energies up to the quasi-elastic peak. The effect
of these contributions in the quasi-free electron scattering process is a
reduction of at most a 3% in the longitudinal response at the energy of the
peak, a value which is below the experimental error and must not be taken into
account in calculations in this energy region. On the other hand, the
excitation of low-lying nuclear levels of neutronic character shows, with
respect to the protonic ones, a considerable effect due to the inclusion of the
two-body term in the charge operator. More realistic calculations, such as
those performed in the random-phase approximation framework, give rise to a
mixing of one particle-one hole configurations of both kinds which reduce these
effects. However, it has been found that the excitation of some of these levels
is sizeably affected by the meson-exchange contribution. More precise
experimental data concerning some of these states, such as e.g. the high-spin
states in 208Pb, could throw some light in the problem of a more feasible
determination of these effects and, as a consequence, could provide an
alternative procedure to obtain the charge neutron form factor.Comment: 26 pages, 10 figures, LateX file and Postscript figure
Analysis of Meson Exchange and Isobar Currents in (e,e'p) Reactions from O-16
An analysis of the effects of meson exchange and isobar currents in exclusive
(e,e'p) processes from O-16 under quasi-free kinematics is presented. A model
that has probed its feasibility for inclusive quasi-elastic (e,e') processes is
considered. Sensitivity to final state interactions between the outgoing proton
and the residual nucleus is discussed by comparing the results obtained with
phenomenological optical potentials and a continuum nuclear shell-model
calculation. The contribution of the meson-exchange and isobar currents to the
response functions is evaluated and compared to previous calculations, which
differ notably from our results. These two-body contributions cannot solve the
puzzle of the simultaneous description of the different responses
experimentally separated. Copyright 1999 by The American Physical SocietyComment: 5 pages, plus 3 PS figures. To be published in Phys. Rev. C Updated
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