633 research outputs found
Test of Fermi Gas Model and Plane-Wave Impulse Approximation Against Electron-Nucleus Scattering Data
A widely used relativistic Fermi gas model and plane-wave impulse
approximation are tested against electron-nucleus scattering data. Inclusive
quasi-elastic cross section are calculated and compared with high-precision
data for C, O, and Ca. A dependence of agreement between calculated cross
section and data on a momentum transfer is shown. Results for the C(nu_mu,mu)
reaction are presented and compared with experimental data of the LSND
collaboration.Comment: 10 pages, 8 figure
Quasi-elastic neutrino charged-current scattering cross sections on oxygen
The charged-current quasi-elastic scattering of muon neutrinos on oxygen
target is computed for neutrino energies between 200 MeV and 2.5 GeV using the
relativistic distorted-wave impulse approximation with relativistic optical
potential, which was earlier successfully applied to describe electron-nucleus
data. We study both neutrino and electron processes and show that the reduced
exclusive cross sections for neutrino and electron scattering are similar. The
comparison with the relativistic Fermi gas model (RFGM), which is widely used
in data analyses of neutrino experiments, shows that the RFGM fails completely
when applied to exclusive cross section data and leads to overestimated values
of inclusive and total cross sections. We also found significant nuclear-model
dependence of exclusive, inclusive and total cross sections for about 1 GeV
energy.Comment: 30 pages, 11 figures; final version to appear in Phys. Rev.
Analysis of quasi-elastic neutrino charged-current scattering off O and neutrino energy reconstruction
The charged-current quasi-elastic scattering of muon neutrino on the oxygen
target is analyzed for neutrino energy up to 2.5 GeV using the Relativistic
Distorted-Wave Impulse Approximation (RDWIA). The inclusive cross sections
, calculated within the RDWIA, are lower than the Relativistic
Fermi Gas Model (RFGM) results in the range of the square of four-momentum
transfer 0.2 (GeV/c). We have also studied the nuclear-model
dependence of the neutrino energy reconstruction accuracy using the
charged-current quasi-elastic events with no detector effects and background.
We found that for one-track events the accuracy is nuclear-model dependent for
neutrino energy up to 2.5 GeV.Comment: 29 pages, 10 figure
Kinetic energy sum spectra in nonmesonic weak decay of hypernuclei
We evaluate the coincidence spectra in the nonmesonic weak decay (NMWD)
\Lambda N\go nN of hypernuclei He, He,
C, O, and Si, as a function of the
sum of kinetic energies for . The strangeness-changing
transition potential is described by the one-meson-exchange model, with
commonly used parameterization. Two versions of the Independent-Particle Shell
Model (IPSM) are employed to account for the nuclear structure of the final
residual nuclei. They are: (a) IPSM-a, where no correlation, except for the
Pauli principle, is taken into account, and (b) IPSM-b, where the highly
excited hole states are considered to be quasi-stationary and are described by
Breit-Wigner distributions, whose widths are estimated from the experimental
data. All and spectra exhibit a series of peaks in the energy
interval 110 MeV MeV, one for each occupied shell-model state.
The IPSM-a could be a pretty fair approximation for the light He
and He hypernuclei. For the remaining, heavier, hypernuclei it is
very important, however, to take into account the spreading in strength of the
deep-hole states, and bring into play the IPSM-b approach. Notwithstanding the
nuclear model that is employed the results depend only very weakly on the
details of the dynamics involved in the decay process proper. We propose that
the IPSM is the appropriate lowest-order approximation for the theoretical
calculations of the of kinetic energy sum spectra in the NMWD. It is in
comparison to this picture that one should appraise the effects of the final
state interactions and of the two-nucleon-induced decay mode.Comment: v1: 20 pages, 3 figures, 1 table, submitted for publication; v2:
minor corrections, improved figures, published versio
Exclusive production in proton-nucleus collisions
The exclusive meson production in a proton-nucleus collision, leading
to two body final states, is investigated in a fully covariant two-nucleon
model based on the effective Lagrangian picture. The explicit kaon production
vertex is described via creation, propagation and decay into relevant channel
of (1650), (1710) and (1720) intermediate baryonic states in the
initial collision of the projectile nucleon with one of its target counterparts
which is modeled by the one-pion exchange process. The calculated cross
sections show strong sensitivity to the medium effects on pion propagator and
to the final hypernuclear state excited in the reaction.Comment: Two new figures, version accepted for publication by Phys. Rev.
Induced Nucleon Polarization and Meson-Exchange Currents in (e,e'p) Reactions
Nucleon recoil polarization observables in reactions are
investigated using a semi-relativistic distorted-wave model which includes one-
and two-body currents with relativistic corrections. Results for the induced
polarization asymmetry are shown for closed-shell nuclei and a comparison with
available experimental data for C is provided. A careful analysis of
meson exchange currents shows that they may affect significantly the induced
polarization for high missing momentum.Comment: 7 pages, 9 figures. Revised version with small changes, new curve in
Fig. 3. To be published in PR
Neutrino and antineutrino charge-exchange reactions on 12C
We extend the formalism of weak interaction processes, obtaining new
expressions for the transition rates, which greatly facilitate numerical
calculations, both for neutrino-nucleus reactions and muon capture. Explicit
violation of CVC hypothesis by the Coulomb field, as well as development of a
sum rule approach for the inclusive cross sections have been worked out. We
have done a thorough study of exclusive (ground state) properties of B
and N within the projected quasiparticle random phase approximation
(PQRPA). Good agreement with experimental data achieved in this way put in
evidence the limitations of standard RPA and the QRPA models, which come from
the inability of the RPA in opening the shell, and from the
non-conservation of the number of particles in the QRPA. The inclusive
neutrino/antineutrino () reactions C(N
and C(B are calculated within both the PQRPA, and
the relativistic QRPA (RQRPA). It is found that the magnitudes of the resulting
cross-sections: i) are close to the sum-rule limit at low energy, but
significantly smaller than this limit at high energies both for and
, ii) they steadily increase when the size of the configuration
space is augmented, and particulary for energies MeV,
and iii) converge for sufficiently large configuration space and final state
spin. The quasi-elastic C(N cross section recently
measured in the MiniBooNE experiment is briefly discussed. We study the
decomposition of the inclusive cross-section based on the degree of
forbiddenness of different multipoles. A few words are dedicated to the
-C charge-exchange reactions related with astrophysical
applications.Comment: 21 pages, 13 figures, 1 table, submitted to Physical Review
Clustering aspects in nuclear structure functions
For understanding an anomalous nuclear effect experimentally observed for the
beryllium-9 nucleus at the Thomas Jefferson National Accelerator Facility
(JLab), clustering aspects are studied in structure functions of deep inelastic
lepton-nucleus scattering by using momentum distributions calculated in
antisymmetrized (or fermionic) molecular dynamics (AMD) and also in a simple
shell model for comparison. According to the AMD, the Be-9 nucleus consists of
two alpha-like clusters with a surrounding neutron. The clustering produces
high-momentum components in nuclear wave functions, which affects nuclear
modifications of the structure functions. We investigated whether clustering
features could appear in the structure function F_2 of Be-9 along with studies
for other light nuclei. We found that nuclear modifications of F_2 are similar
in both AMD and shell models within our simple convolution description although
there are slight differences in Be-9. It indicates that the anomalous Be-9
result should be explained by a different mechanism from the nuclear binding
and Fermi motion. If nuclear-modification slopes d(F_2^A/F_2^D)/dx are shown by
the maximum local densities, the Be-9 anomaly can be explained by the AMD
picture, namely by the clustering structure, whereas it certainly cannot be
described in the simple shell model. This fact suggests that the large nuclear
modification in Be-9 should be explained by large densities in the clusters.
For example, internal nucleon structure could be modified in the high-density
clusters. The clustering aspect of nuclear structure functions is an unexplored
topic which is interesting for future investigations.Comment: 11 pages, LaTeX, 10 eps files, Physical Review C in pres
- …