660 research outputs found

### Weak reactions on 12C within the Continuum Random Phase Approximation with partial occupancies

We extend our previous studies of the neutrino-induced reactions on 12C and
muon capture to include partial occupation of nuclear subshells in the
framework of the continuum random phase approximation. We find, in contrast to
the work by Auerbach et al., that a partial occupation of the p1/2 subshell
reduces the inclusive cross sections only slightly. The extended model
describes the muon capture rate and the 12C(nu_e,e-)12N cross section very
well. The recently updated flux and the improved model bring the calculated
12C(nu_mu,mu^-)12N cross section (~ 17.5 10^{-40} cm^2) and the data (12.4 +/-
0.3(stat.) +/- 1.8(syst.) 10^{-40} cm^2) closer together, but does not remove
the discrepancy fully.Comment: 12 pages, 2 figure

### Estimates of weak and electromagnetic nuclear decay signatures for neutrino reactions in Super-Kamiokande

We estimate possible delayed β decay signatures of the neutrino induced reactions on 16O in a two-step model: the primary neutrino (ν,l) process, where l is the lepton in the final state, is described within the random phase approximation, while the subsequent decay of the excited nuclear state in the final channel is treated within the statistical model. We calculate partial reaction cross sections leading to β unstable nuclei. We consider neutrino energies up to 500 MeV, relevant for atmospheric neutrino detection in Super-Kamiokande, and supernova neutrino spectra

### Neutrino-nucleus reactions and their role for supernova dynamics and nucleosynthesis

The description of nuclear reactions induced by supernova neutrinos has
witnessed significant progress during the recent years. At the energies and
momentum transfers relevant for supernova neutrinos neutrino-nucleus cross
sections are dominated by allowed transitions, however, often with
non-negligible contributions from (first) forbidden transitions. For several
nuclei allowed Gamow-Teller strength distributions could be derived from
charge-exchange reactions and from inelastic electron scattering data.
Importantly the diagonalization shell model has been proven to accurately
describe these data and hence became the appropriate tool to calculate the
allowed contributions to neutrino-nucleus cross sections for supernova
neutrinos. Higher multipole contributions are usually calculated within the
framework of the Quasiparticle Random Phase Approximation, which describes the
total strength and the position of the giant resonances quite well.
This manuscript reviews the recent progress achieved in calculating
supernova-relevant neutrino-nucleus cross sections and discusses its
verification by data. Moreover, the review summarizes also the impact which
neutrino-nucleus reactions have on the dynamics of supernovae and on the
associated nucleosynthesis. These include the absorption of neutrinos by nuclei
(the inverse of nuclear electron capture which is the dominating
weak-interaction process during collapse), inelastic neutrino-nucleus
scattering and nuclear de-excitation by neutrino-pair emission. We also discuss
the role of neutrino-induced reactions for the recently discovered $\nu p$
process, for the r-process and for the neutrino process, for which
neutrino-nucleus reactions have the largest impact. Finally, we briefly review
neutrino-nucleus reactions important for the observation of supernova neutrinos
by earthbound detectors. (Abridged)Comment: 77 pages, 29 figures, 4 tables, submitted to Progress in Particle and
Nuclear Physic

### Quasielastic neutrino scattering from oxygen and the atmospheric neutrino problem

We examine several phenomena beyond the scope of Fermi-gas models that affect
the quasielastic scattering (from oxygen) of neutrinos in the 0.1 -- 3.0 GeV
range. These include Coulomb interactions of outgoing protons and leptons, a
realistic finite-volume mean field, and the residual nucleon-nucleon
interaction. None of these effects are accurately represented in the Monte
Carlo simulations used to predict event rates due to $\mu$ and $e$ neutrinos
from cosmic-ray collisions in the atmosphere. We nevertheless conclude that the
neglected physics cannot account for the anomalous $\mu$ to $e$ ratio observed
at Kamiokande and IMB, and is unlikely to change absolute event rates by more
than 10--15\%. We briefly mention other phenomena, still to be investigated in
detail, that may produce larger changes.Comment: In Revtex version 2. 14 pages, 3 figures (available on request from
J. Engel, tel. 302-831-4354, [email protected]

### Shell Model Monte Carlo Methods

We review quantum Monte Carlo methods for dealing with large shell model
problems. These methods reduce the imaginary-time many-body evolution operator
to a coherent superposition of one-body evolutions in fluctuating one-body
fields; the resultant path integral is evaluated stochastically. We first
discuss the motivation, formalism, and implementation of such Shell Model Monte
Carlo (SMMC) methods. There then follows a sampler of results and insights
obtained from a number of applications. These include the ground state and
thermal properties of {\it pf}-shell nuclei, the thermal and rotational
behavior of rare-earth and $\gamma$-soft nuclei, and the calculation of double
beta-decay matrix elements. Finally, prospects for further progress in such
calculations are discussed

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