Showing papers by "Petr Vogel published in 1993"

Quasielastic neutrino scattering from oxygen and the atmospheric neutrino problem.

Abstract: 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 μ and e neutrinos from cosmic-ray collisions in the atmosphere. We nevertheless conclude that the neglected physics cannot account for the anomalous μ-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.

Nuclear structure and double beta decay

Abstract: Study of the neutrinoless double beta decay, 0νββ, includes a variety of problems of nuclear structure theory. They are reviewed here. The problems range from the mechanism of the decay, i.e. exchange of the light Majorana neutrino versus the exchange of some heavy, so far unobserved particle. Next, the proper expressions for the corresponding operator are described that should include the effects of the nucleon size and of the recoil order terms in the hadronic current. The issue of proper treatment of the short range correlations, in particular for the case of the heavy particle exchange, is discussed also. The variety of methods employed these days in the theoretical evaluation of the nuclear matrix elements M^(0ν) is briefly described and the difficulties causing the spread and hence uncertainty in the values of M^(0ν) are discussed. Finally, the issue of the axial current quenching, and of the resonance enhancement in the case of double electron capture are described.

Spin-isospin SU(4) symmetry in sd- and fp-shell nuclei.

Abstract: For all even-A nuclei in the sd shell we evaluate the overlap between several low-lying states, obtained by diagonalizing the realistic Wildenthal interaction, and the eigenstates of the SU(4) Casimir operator. We find that the J=0+ ground states of even-even nuclei near the middle of the shell have rather small overlaps (less than 0.5) with the lowest SU(4) Young tableaux, while the J=0+ and 1+ lowest states of odd-odd nuclei have noticeably larger overlaps (0.6–0.7). We also find that the expansion in the SU(4) Young tableaux converges quite rapidly, and that the two or three lowest tableaux usually account for more than 90% of the nuclear wave function. We then extend the calculation to the fp shell and evaluate the overlaps between the J=0+ ground states obtained by diagonalizing a realistic interaction and the SU(4) eigenstates for even-even nuclei with maximum isospin. For the fp shell the overlaps are even smaller than in the sd shell. Since we observe such sizable SU(4) symmetry breaking effects in the relatively simple sd and pf nuclei, we are rather pessimistic about the prospects of using conclusions based on SU(4) in heavier, more complex nuclei.

A low-energy neutrino oscillation detector at the San Onofre nuclear reactor

Abstract: The San Onofre experiment consists of a large liquid scintillation detector for studying neutrino oscillations with a projected sensitivity for �m2 of 10-3e V2 and a mixing angle sensitivity of sin220 = 01 The detector is a segmented 13 ton liquid scintillator A novel scheme of neutron background rejection based on a positron annihilation coincidence requirement has been developed Our detector will be installed at a distance of 650 m from the San Onofre reactors in Southern California, 20 mwe below surface We employ a passive neutron buffer and an active muon veto to reduce the background The event rate is expected to be 22/d with a signal-to-background of about 2 : 1

Nuclear detection of galactic dark matter

Abstract: The elastic scattering of weak1y interacting dark matter particles (assumed to be "neutralinos" -neutral fermions predicted by supersymmetry theories) from nuclei is described. The cross sections associated with this process will govern count rates in laboratory experiments. Particular empbasis is given to a proper description of the structure of the detector nuclei. A brief discussion of the prospects for detecting neutralinos in the next few years is given.