3,876 research outputs found
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.
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
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
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
Role of 2p-2h MEC excitations in superscaling
Following recent studies of inclusive electron scattering from nuclei at high
energies which focused on two-nucleon emission mediated by meson-exchange
currents, in this work the superscaling behavior of such contributions is
investigated. Comparisons are made with existing data below the quasielastic
peak where at high momentum transfers scaling of the second kind is known to be
excellent and scaling of the first kind is good, in the proximity of the peak
where both 1p-1h and 2p-2h contributions come into play, and above the peak
where inelasticity becomes important and one finds scaling violations of the
two kinds.Comment: 27 pages, 12 figures; references adde
Superscaling and neutral current quasielastic neutrino-nucleus scattering
The superscaling approach is applied to studies of neutral current neutrino
reactions in the quasielastic regime. Using input from scaling analyses of
electron scattering data, predictions for high-energy neutrino and antineutrino
cross sections are given and compared with results obtained using the
relativistic Fermi gas model. The influence of strangeness content inside the
nucleons in the nucleus is also explored.Comment: 28 pages, 8 figures, accepted for publication in Phys.Rev.
Radiative pion capture in nuclei: a continuum shell-model approach
The radiative pion capture process in nuclei is approached by using a
continuum shell-model description of the nucleus, together with a
phenomenological treatment of the two particle-two hole effects. It is found
that these effects play an important role to reproduce the observed
experimental photon energy distribution. This distribution as well as the
integrated one depends significantly on the details of the mean field
potential. This makes this process interesting to investigate the nuclear
structure dynamics.Comment: 21 pages, LateX file + 5 figures, epsf.st
A model of short-range correlations in the charge response
The validity of a model treating the short-range correlations up to the first
order is studied by calculating the charge response of an infinite system and
comparing the obtained results with those of a Fermi Hypernetted Chain
calculation.Comment: 6 pages, 3 Postscript figures, to be published on Phys. Rev.
Using Electron Scattering Superscaling to predict Charge-changing Neutrino Cross Sections in Nuclei
Superscaling analyses of few-GeV inclusive electron scattering from nuclei
are extended to include not only quasielastic processes, but now also into the
region where -excitation dominates. It is shown that, with reasonable
assumptions about the basic nuclear scaling function extracted from data and
information from other studies of the relative roles played by correlation and
MEC effects, the residual strength in the resonance region can be accounted for
through an extended scaling analysis. One observes scaling upon assuming that
the elementary cross section by which one divides the residual to obtain a new
scaling function is dominated by the transition and employing a
new scaling variable which is suited to the resonance region. This yields a
good representation of the electromagnetic response in both the quasielastic
and regions. The scaling approach is then inverted and predictions are
made for charge-changing neutrino reactions at energies of a few GeV, with
focus placed on nuclei which are relevant for neutrino oscillation
measurements. For this a relativistic treatment of the required weak
interaction vector and axial-vector currents for both quasielastic and
-excitation processes is presented.Comment: 42 pages, 9 figures, accepted for publication in Physical Review
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