26 research outputs found
Nuclear transparencies in relativistic A(e,e'p) models
Relativistic and unfactorized calculations for the nuclear transparency
extracted from exclusive A(e,e'p) reactions for 0.3 \leq Q^2 \leq 10 (GeV/c)^2
are presented for the target nuclei C, Si, Fe and Pb. For Q^2 \geq 0.6
(GeV/c)^2, the transparency results are computed within the framework of the
recently developed relativistic multiple-scattering Glauber approximation
(RMSGA). The target-mass and Q^2 dependence of the RMSGA predictions are
compared with relativistic distorted-wave impulse approximation (RDWIA)
calculations. Despite the very different model assumptions underlying the
treatment of the final-state interactions in the RMSGA and RDWIA frameworks,
they predict comparable nuclear transparencies for kinematic regimes where both
models are applicable.Comment: 15 pages, 4 figure
Correlations and the Cross Section of Exclusive () Reactions for O
The reduced cross section for exclusive () reactions has been studied
in DWIA for the example of the nucleus O using a spectral function
containing effects of correlations. The spectral function is evaluated directly
for the finite nucleus starting from a realistic nucleon-nucleon interaction
within the framework of the Green's function approach. The emphasis is focused
on the correlations induced by excitation modes at low energies described
within a model-space of shell-model configurations including states up to the
shell. Cross sections for the -wave quasi-hole transitions at low
missing energies are presented and compared with the most recent experimental
data. In the case of the so-called perpendicular kinematics the reduced cross
section derived in DWIA shows an enhancement at high missing momenta as
compared to the PWIA result. Furthermore the cross sections for the - and
-wave quasi-hole transitions are presented and compared to available data at
low missing momenta. Also in these cases, which cannot be described in a model
without correlations, a good agreement with the experiment is obtained.Comment: 12 pages, LaTeX, 4 figures include
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.
Meson Exchange Currents in (e,e'p) recoil polarization observables
A study of the effects of meson-exchange currents and isobar configurations
in reactions is presented. We use a distorted wave
impulse approximation (DWIA) model where final-state interactions are treated
through a phenomenological optical potential. The model includes relativistic
corrections in the kinematics and in the electromagnetic one- and two-body
currents. The full set of polarized response functions is analyzed, as well as
the transferred polarization asymmetry. Results are presented for proton
knock-out from closed-shell nuclei, for moderate to high momentum transfer.Comment: 44 pages, 18 figures. Added physical arguments explaining the
dominance of OB over MEC, and a summary of differences with previous MEC
calculations. To be published in PR
Polarization transfer in the HeH reaction
Polarization transfer in the 4He(e,e'p)3H reaction at a Q^2 of 0.4 (GeV/c)^2
was measured at the Mainz Microtron MAMI. The ratio of the transverse to the
longitudinal polarization components of the ejected protons was compared with
the same ratio for elastic ep scattering. The results are consistent with a
recent fully relativistic calculation which includes a predicted medium
modification of the proton form factor based on a quark-meson coupling model.Comment: 5 pages, Latex, 2 postscript figures, submitted to Physics Letters
The USCT reference database
Ultrasound Computer Tomography (USCT) is an emerging technology mostly aimed at breast cancer imaging. Following the idea of open science a USCT reference database is established with open and easy to use data and code interfaces. The aim is to promote and facilitate the exchange of available reconstruction algorithms and raw data sets from different USCT devices throughout the growing USCT community. Additionally, the feedback about data and system architecture of the scientists working on reconstruction methods will be published online to help to drive further development of the various measurement setups
Nuclear Medium Effects in the Relativistic Treatment of Quasifree Electron Scattering
Non-relativistic reduction of the S-matrix for the quasifree electron
scattering process is studied in order to
understand the source of differences between non-relativistic and relativistic
models. We perform an effective Pauli reduction on the relativistic expression
for the S-matrix in the one-photon exchange approximation. The reduction is
applied to the nucleon current only; the electrons are treated fully
relativistically. An expansion of the amplitude results in a power series in
the nuclear potentials. The series is found to converge rapidly only if the
nuclear potentials are included in the nuclear current operator. The results
can be cast in a form which reproduces the non-relativistic amplitudes in the
limit that the potentials are removed from the nuclear current operator. Large
differences can be found between calculations which do and do not include the
nuclear potentials in the different orders of the nuclear current operator. In
the high missing momentum region we find that the non-relativistic calculations
with potentials included in the nuclear current up to second order give results
which are close to those of the fully relativistic calculation. This behavior
is an indication of the importance of the medium modifications of the nuclear
currents in this model, which are naturally built into the relativistic
treatment of the reaction.Comment: Latex, 26 pages including 5 uuencoded postscript figures. accepted
for publication in Phys. Rev. C
Superscaling predictions for neutrino-induced charged-current charged pion production at MiniBooNE
Superscaling approximation (SuSA) predictions to neutrino-induced
charged-current charged pion production in the \Delta-resonance region are
explored under MiniBooNE experimental conditions. The results obtained within
SuSA for the flux-averaged double-differential cross sections of the \pi+
production for the \nu_\mu+CH_2 reaction as a function of the muon kinetic
energy and of the scattering angle, the cross sections averaged over the angle,
the total cross section for the \pi+ production, as well as CC1\pi+ to CCQE
cross section ratio are compared with the corresponding MiniBooNE experimental
data. The SuSA predictions are in good agreement with data on neutrino flux
average cross-sections, but a somewhat different dependence on the neutrino
energy is predicted than the one resulting from the experimental analysis.Comment: 15 pages, 6 figures, accepted for publication in Physics Letters
Nuclear isospin mixing and elastic parity-violating electron scattering
The influence of nuclear isospin mixing on parity-violating elastic electron
scattering is studied for the even-even, N=Z nuclei 12C, 24Mg, 28Si, and 32S.
Their ground-state wave functions have been obtained using a self-consistent
axially-symmetric mean-field approximation with density-dependent effective
two-body Skyrme interactions. Some differences from previous shell-model
calculations appear for the isovector Coulomb form factors which play a role in
determining the parity-violating asymmetry. To gain an understanding of how
these differences arise, the results have been expanded in a spherical harmonic
oscillator basis. Results are obtained not only within the plane-wave Born
approximation, but also using the distorted-wave Born approximation for
comparison with potential future experimental studies of parity-violating
electron scattering. To this end, for each nucleus the focus is placed on
kinematic ranges where the signal (isospin-mixing effects on the
parity-violating asymmetry) and the experimental figure-of-merit are maximized.
Strangeness contributions to the asymmetry are also briefly discussed, since
they and the isospin mixing contributions may play comparable roles for the
nuclei being studied at the low momentum transfers of interest in the present
work.Comment: 25 pages, 9 figure
ORBITAL 1+ STRENGTHS FROM SELF-CONSISTENT DEFORMED MEAN FIELD CALCULATIONS
We present results for summed orbital 1+ strengths in Sm and Nd isotopes obtained from deformed Hartree-Fock + BCS calculations, using a microscopic formulation of the scissors mode (the PHFB model) that excludes spurious contributions. It is found that the calculated 1+ strengths for the two chains of isotopes are proportional to delta-2 and that the summed strengths up to 4 MeV are in fair agreement with experimental data. It is also found that when pairing is neglected the total scissors mode strength is proportional to delta-rather than to delta-2. Analytical expressions are given for the explicit dependence on the deformation parameter with and without pairing, valid for the anisotropic harmonic oscillator model.Peer reviewe