47 research outputs found
Results from the NEMO 3 experiment
The aim of the NEMO 3 experiment is the search for neutrinoless double beta
decay and precise measurement of two-neutrino double beta decay of several
isotopes. The experiment has been taking data since 2003. Since no evidence for
neutrinoless double beta decay of Mo100 and Se82 has been found, a 90% C.L.
lower limit on the half-life of this process and corresponding upper limit on
the effective Majorana neutrino mass are derived. The data are also interpreted
in terms of alternative models, such as weak right-handed currents or Majoron
emission. In addition, NEMO 3 has performed precision measurements of the
two-neutrino double beta decay for seven different isotopes. The most recent
experimental results of NEMO 3 are presented in this paper.Comment: 5 pages, 2 tables, talk at the 10th ICATPP Conference (Como, Italy, 8
- 12 October 2007
Sharpening Low-Energy, Standard-Model Tests via Correlation Coefficients in Neutron Beta-Decay
The correlation coefficients a, A, and B in neutron beta-decay are
proportional to the ratio of the axial-vector to vector weak coupling
constants, g_A/g_V, to leading recoil order. With the advent of the next
generation of neutron decay experiments, the recoil-order corrections to these
expressions become experimentally accessible, admitting a plurality of Standard
Model (SM) tests. The measurement of both a and A, e.g., allows one to test the
conserved-vector-current (CVC) hypothesis and to search for second-class
currents (SCC) independently. The anticipated precision of these measurements
suggests that the bounds on CVC violation and SCC from studies of nuclear
beta-decay can be qualitatively bettered. Departures from SM expectations can
be interpreted as evidence for non-V-A currents.Comment: 4 pages, REVTeX, intro. broadened, typos fixed, to appear in PR
Selection rules in the double beta decay of deformed nuclei
The 2 nu double beta decay half-lives of six nuclei, whose decays were
previously reported as theoretically forbidden, are calculated by including the
pairing interaction, which mixes different occupations and opens up the
possibility of the decay. All allowed channels for the 0 nu double beta decay
are also computed. The estimated 2 nu double beta half-lives suggest that
measurements in 244Pu may find positive signals, and that planned experiments
would succeed in detecting the 2 nu double beta decay in 160Gd. Limits for the
zero neutrino mode, in the analyzed deformed emitters, are predicted.Comment: 4 pages, 4 table
Shape of the 8B Alpha and Neutrino Spectra
The beta-delayed alpha spectrum from the decay of 8B has been measured with a
setup that minimized systematic uncertainties that affected previous
measurements. Consequently the deduced neutrino spectrum presents much smaller
uncertainties than the previous recommendation. The 8B neutrino spectrum is
found to be harder than previously recommended with about (10-20)% more
neutrinos at energies between 12-14 MeV. The efficiencies of the 37Cl, 71Ga,
40Ar, and SuperKamiokande detectors are respectively, 3.6%, 1.4%, 5.7% and 1.8%
larger than previously thought.Comment: 4 pages, 5 figure
Search for EC and ECEC processes in Sn and decay of Sn to the excited states of Te
Limits on EC and ECEC processes in Sn and on
decay of Sn to the excited states of Te have
been obtained using a 380 cm HPGe detector and an external source
consisting of natural tin. A limit with 90% C.L. on the Sn half-life of
y for the ECEC(0) transition to the excited
state in Cd (1871.0 keV) has been established. This transition is
discussed in the context of a possible enhancement of the decay rate by several
orders of magnitude given that the ECEC process is nearly degenerate
with an excited state in the daughter nuclide. Prospects for investigating such
a process in future experiments are discussed. The decay
limits for Sn to the excited states of Te were obtained on the
level of y at the 90% C.L.Comment: 17 pages, 5 figure
New Results for Double-Beta Decay of Mo-100 to Excited Final States of Ru-100 Using the TUNL-ITEP Apparatus
The coincidence detection efficiency of the TUNL--ITEP apparatus designed for
measuring half-life times of two-neutrino double-beta decay transitions to
excited final states in daughter nuclei has been measured with a factor of 2.4
improved accuracy. In addition, the previous measuring time of 455 days for the
study of the Mo-100 two-neutrino double-beta decay to the first excited 0+
state in Ru-100 has been increased by 450 days, and a new result (combined with
the previous measurement obtained with the same apparatus) for this transition
is presented: T_(1/2) = [5.5 (+1.2/-0.8) (stat) +/- 0.3 (syst)] x 10^20 y.
Measured two-neutrino double-beta decay half-life times to excited states can
be used to test the reliability of nuclear matrix element calculations needed
for determining the effective neutrino mass from zero-neutrino double-beta
decay data. We also present new limits for transitions to higher excited states
in Ru-100 which, if improved, may be of interest for more exotic conjectures,
like a bosonic component to neutrino statistics
Solar Fusion Cross Sections
We review and analyze the available information for nuclear fusion cross
sections that are most important for solar energy generation and solar neutrino
production. We provide best values for the low-energy cross-section factors
and, wherever possible, estimates of the uncertainties. We also describe the
most important experiments and calculations that are required in order to
improve our knowledge of solar fusion rates.Comment: LaTeX file, 48 pages (figures not included). To appear in Rev. Mod.
Phys., 10/98. All authors now listed. Full postscript version with figures
available at http://www.sns.ias.edu/~jnb/Papers/Preprints/nuclearfusion.htm
Large-basis shell-model calculations for p-shell nuclei
Results of large-basis shell-model calculations for nuclei with A=7-11 are
presented. The effective interactions used in the study were derived
microscopically from the Reid93 potential and take into account the Coulomb
potential as well as the charge dependence of T=1 partial waves. For A=7, a
model space was used, while for the rest of the studied
nuclides, the calculations were performed in a model space. It
is demonstrated that the shell model combined with microscopic effective
interactions derived from modern nucleon-nucleon potentials is capable of
providing good agreement with the experimental properties of the ground state
as well as with those of the low-lying excited states.Comment: 17 pages. REVTEX. 16 PostScript figure