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

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]

Neutrino–nucleus reactions and nuclear structure

The methods used in the evaluation of the neutrino–nucleus cross section are reviewed. Results are shown for a variety of targets of practical importance. Many of the described reactions are accessible in future experiments with neutrino sources from the pion and muon decays at rest, which might be available at the neutron spallation facilities. Detailed comparison between the experimental and theoretical results would establish benchmarks needed for verification and/or parameter adjustment of the nuclear models. Having a reliable tool for such calculation is of great importance in a variety of applications, e.g. the neutrino oscillation studies, detection of supernova neutrinos, description of the neutrino transport in supernovae and description of the r-process nucleosynthesis

Pairing and Isospin Symmetry in Proton-Rich Nuclei

Unlike their lighter counterparts, most odd-odd N=Z nuclei with mass A > 40 40 have ground states with isospin T=1, suggesting an increased role for the isovector pairing interaction. A simple SO(5) seniority-like model of this interaction reveals a striking and heretofore unnoticed interplay between like-particle and neutron-proton isovector pairing near N=Z that is reflected in the number of each kind of pair as a function of A and T. Large scale shell-model calculations exhibit the same trends, despite the simultaneous presence of isoscalar pairs, deformation, and other correlations.Comment: 8 pages + 2 postscript figures, in RevTeX. Discussion of isospin projection in HFB added. This version to appear in Phys. Lett.

Systematic thermal reduction of neutronization in core-collapse supernovae

We investigate to what extent the temperature dependence of the nuclear symmetry energy can affect the neutronization of the stellar core prior to neutrino trapping during gravitational collapse. To this end, we implement a one-zone simulation to follow the collapse until beta equilibrium is reached and the lepton fraction remains constant. Since the strength of electron capture on the neutron-rich nuclei associated to the supernova scenario is still an open issue, we keep it as a free parameter. We find that the temperature dependence of the symmetry energy consistently yields a small reduction of deleptonization, which corresponds to a systematic effect on the shock wave energetics: the gain in dissociation energy of the shock has a small yet non-negligible value of about 0.4 foe (1 foe = 10^51 erg) and this result is almost independent from the strength of nuclear electron capture. The presence of such a systematic effect and its robustness under changes of the parameters of the one-zone model are significative enough to justify further investigations with detailed numerical simulations of supernova explosions.Comment: 15 pages, 2 tables, 3 figure

Neutrino-induced nucleosynthesis and the site of the r process

If the r process occurs deep within a type II supernova, probably the most popular of the proposed sites, abundances of r-process elements may be altered by the intense neutrino flux. We point out that the effects would be especially pronounced for eight isotopes that can be efficiently synthesized by the neutrino reactions following r-process freeze-out. We show that the observed abundances of these isotopes are entirely consistent with neutrino-induced nucleosynthesis, strongly arguing for a supernova r-process site. The deduced neutrino fluences place stringent constraints on the freeze-out radius and dynamic time scale of the r process