199 research outputs found
Spin Observables in Coincidence Electron Scattering from Nuclei I: Reduced Response Functions
A theoretical description of nucleon knockout reactions initiated by
polarized electron scattering from polarized nuclei is presented. Explicit
expressions for the complete set of reduced response functions (independent of
the polarization angle) that can be experimentally obtained assuming plane
waves for the electron are given in a general multipole expansion. The
formalism is applied to the particular case of closed-shell-minus-one nuclei
using two models for the ejected nucleon, including the final-state interaction
phenomenologically with a complex optical potential and in the factorized
plane-wave impulse approximation. Relativistic effects in the kinematics and in
the electromagnetic current are incorporated throughout --- specifically a new
expansion of the electromagnetic current in powers only of the struck nucleon
momentum is employed. Results are presented for the nucleus 39K.Comment: 51 pages (LaTeX), 17 figures (postScript
Superscaling and Charge-changing Neutrino Cross Sections
The superscaling function extracted from inclusive electron scattering data
is used to predict high energy charge-changing neutrino cross sections in the
quasi-elastic and regions.Comment: 3 pages, 2 figures, to appear in the Proceedings of the 7th
International Workshop on Neutrino Factories and Superbeams, Laboratori
Nazionali di Frascati, Frascati (Rome), June 21 - 26, 200
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
Scaling and isospin effects in quasielastic lepton-nucleus scattering in the Relativistic Mean Field Approach
The role of isospin in quasielastic electron scattering and charge-changing
neutrino reactions is investigated in the relativistic impulse approximation.
We analyze proton and neutron scaling functions making use of various
theoretical descriptions for the final-state interactions, focusing on the
effects introduced by the presence of strong scalar and vector terms in the
relativistic mean field approach. An explanation for the differences observed
in the scaling functions evaluated from and reactions is
provided by invoking the differences in isoscalar and isovector contributions.Comment: 10 pages, 5 figures, submitted to Phys. Lett.
Relativistic pionic effects in quasielastic electron scattering
The impact of relativistic pionic correlations and meson-exchange currents on
the response functions for electromagnetic quasielastic electron scattering
from nuclei is studied in detail. Results in first-order perturbation theory
are obtained for one-particle emission electronuclear reactions within the
context of the relativistic Fermi gas model. Improving upon previous analyses
where non-relativistic reductions of the currents were performed, here a fully
relativistic analysis in which both forces and currents are treated
consistently is presented. Lorentz covariance is shown to play a crucial role
in enforcing the gauge invariance of the theory. Effects stemming uniquely from
relativity in the pionic correlations are identified and, in particular, a
comprehensive study of the self-energy contributions and of the currents
associated with the pion is presented. First- and second-kind scaling for high
momentum transfer is investigated.Comment: 43 pages, 21 figure
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
Electron helicity-dependence in (e,e'p) reactions with polarized nuclei and the fifth response function
The cross section for electron-induced proton knockout reactions with
polarized beam and target is computed in a DWIA model. The analysis is focused
on the electron helicity-dependent (HD) piece of the cross section. For the
case of in-plane emission a new symmetry is found in the HD cross section,
which takes opposite values for specific opposing pairs of nuclear
orientations, explaining why the fifth response (involving polarized electrons,
but unpolarized nuclei) is zero for this choice of kinematics. Even when this
symmetry breaks down in the case of nucleon emission out of the scattering
plane, it is shown that it is still present in the separate response functions.
A physical explanation of these results is presented using a semi-classical
model of the reaction based on the PWIA and on the concept of a nucleon orbit
with its implied expectation values of position and spin.Comment: 38 pages, 15 PS figure
Meson-exchange currents and quasielastic neutrino cross sections in the SuperScaling Approximation model
We evaluate the quasielastic double differential neutrino cross sections
obtained in a phenomenological model based on the superscaling behavior of
electron scattering data. We compare our results with the recent experimental
data for neutrinos of MiniBooNE and estimate the contribution of the vector
meson-exchange currents in the 2p-2h sector.Comment: 6 pages, 4 figure
Extended Superscaling of Electron Scattering from Nuclei
An extended study of scaling of the first and second kinds for inclusive
electron scattering from nuclei is presented. Emphasis is placed on the
transverse response in the kinematic region lying above the quasielastic peak.
In particular, for the region in which electroproduction of resonances is
expected to be important, approximate scaling of the second kind is observed
and the modest breaking of it is shown probably to be due to the role played by
an inelastic version of the usual scaling variable.Comment: LaTeX, 36 pages including 5 color postscript figures and 4 postscript
figure
Delta-isobar relativistic meson exchange currents in quasielastic electron scattering
We study the role of the -isobar current on the response functions
for high energy inclusive quasielastic electron scattering from nuclei. We
consider a general Lagrangian which is compatible with contact invariance and
perform a fully relativistic calculation in first-order perturbation theory for
one-particle emission. The dependence of the responses upon off-shell
parametrizations is analyzed and found to be mild. A discussion of scaling
behaviour and a comparison with various non-relativistic approaches are also
presented.Comment: 26 pages, 9 figures; one page of text added; corrected errors in eq
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