1,649 research outputs found
High sensitivity GEM experiment on double beta decay of 76-Ge
The GEM project is designed for the next generation 2 beta decay experiments
with 76-Ge. One ton of ''naked'' HP Ge detectors (natural at the first GEM-I
phase and enriched in 76-Ge to 86% at the second GEM-II stage) are operating in
super-high purity liquid nitrogen contained in the Cu vacuum cryostat (sphere
with diameter 5 m). The latest is placed in the water shield. Monte Carlo
simulation evidently shows that sensitivity of the experiment (in terms of the
T1/2 limit for neutrinoless 2 beta decay) is 10^27 yr with natural HP Ge
crystals and 10^28 yr with enriched ones. These bounds corresponds to the
restrictions on the neutrino mass less than 0.05 eV and 0.015 eV with natural
and enriched detectors, respectively. Besides, the GEM-I set up could advance
the current best limits on the existence of neutralinos - as dark matter
candidates - by three order of magnitudes, and at the same time would be able
to identify unambiguously the dark matter signal by detection of its seasonal
modulation.Comment: LaTeX, 20 pages, 4 figure
Double-beta decay matrix elements for
Double-beta decay matrix elements (ME) for are calculated with different quasi random phase approximation (QRPA)-based methods. First, the ME for the two-neutrino mode are computed using two choices for the single particle (s.p.) basis: i) full shells and ii) full shells. When calculated with the renormalized QRPA (RQRPA) and full-RQRPA their values are rather dependent on the size of the single particle basis used, while calculated with proton-neutron QRPA (pnQRPA) and second-QRPA approaches such a dependence was found to be small. The Ikeda sum rule was well fulfilled within pnQRPA for both choices of the s.p. basis and with a good approximation within second-QRPA, while the RQRPA and full-RQRPA methods give deviations up to 21%. Further, the ME for the neutrinoless mode are calculated with the pnQRPA, RQRPA and full-RQRPA methods. They all give close results for the calculation with the smaller basis (i), while for the larger basis (ii), the results differ significantly either from one method to another or within the same method. Finally, using the most recent experimental limit for the decay half-life of a critical discussion on the upper limits for the neutrino mass parameter obtained with different theoretical approaches is given
Shell-model calculations of two-neutrino double-beta decay rates of Ca with GXPF1A interaction
The two-neutrino double beta decay matrix elements and half-lives of
Ca, are calculated within a shell-model approach for transitions to the
ground state and to the first excited state of Ti. We use the full
model space and the GXPF1A interaction, which was recently proposed to
describe the spectroscopic properties of the nuclei in the nuclear mass region
A=47-66. Our results are =
and = . The result for the
decay to the Ti 0 ground state is in good agreement with experiment.
The half-life for the decay to the 2 state is two orders of magnitude
larger than obtained previously.Comment: 6 pages, 4 figure
Low Energy Neutrino Physics after SNO and KamLAND
In the recent years important discoveries in the field of low energy neutrino
physics (E in the MeV range) have been achieved. Results of the
solar neutrino experiment SNO show clearly flavor transitions from to
. In addition, the long standing solar neutrino problem is
basically solved. With KamLAND, an experiment measuring neutrinos emitted from
nuclear reactors at large distances, evidence for neutrino oscillations has
been found. The values for the oscillation parameters, amplitude and phase,
have been restricted. In this paper the potential of future projects in low
energy neutrino physics is discussed. This encompasses future solar and reactor
experiments as well as the direct search for neutrino masses. Finally the
potential of a large liquid scintillator detector in an underground laboratory
for supernova neutrino detection, solar neutrino detection, and the search for
proton decay is discussed.Comment: Invited brief review, World Scientific Publishing Compan
Structure of Pairs in Heavy Weakly-Bound Nuclei
We study the structure of nucleon pairs within a simple model consisting of a
square well in three dimensions and a delta-function residual interaction
between two weakly-bound particles at the Fermi surface. We include the
continuum by enclosing the entire system in a large spherical box. To a good
approximation, the continuum can be replaced by a small set of
optimally-determined resonance states, suggesting that in many nuclei far from
stability it may be possible to incorporate continuum effects within
traditional shell-model based approximations.Comment: REVTEX format, 9 pages, 2 figures, 2 table
Double Beta Decay, Majorana Neutrinos, and Neutrino Mass
The theoretical and experimental issues relevant to neutrinoless double-beta
decay are reviewed. The impact that a direct observation of this exotic process
would have on elementary particle physics, nuclear physics, astrophysics and
cosmology is profound. Now that neutrinos are known to have mass and
experiments are becoming more sensitive, even the non-observation of
neutrinoless double-beta decay will be useful. If the process is actually
observed, we will immediately learn much about the neutrino. The status and
discovery potential of proposed experiments are reviewed in this context, with
significant emphasis on proposals favored by recent panel reviews. The
importance of and challenges in the calculation of nuclear matrix elements that
govern the decay are considered in detail. The increasing sensitivity of
experiments and improvements in nuclear theory make the future exciting for
this field at the interface of nuclear and particle physics.Comment: invited submission to Reviews of Modern Physics, higher resolution
figures available upon request from authors, Version 2 has fixed typos and
some changes after referee report
Radiative corrections to neutrino mass matrix in the Standard Model and beyond
We study the effect of radiative corrections on the structure of neutrino
mass matrix. We analyze the renormalization of the matrix from the electroweak
scale to the scale at which the effective operator that gives
masses to neutrinos is generated. Apart from Standard Model and MSSM,
non-standard extensions of SM are considered at a scale intermediate
between and . We find that the dominant structure of the neutrino
mass matrix does not change. SM and MSSM corrections produce small (few
percents) independent renormalization of each matrix element. Non-standard
(flavor changing) corrections can modify strongly small (sub-dominant) matrix
elements, which are important for the low energy phenomenology. In particular,
we show that all sub-dominant elements can have purely radiative origin, being
zero at . The set of non-zero elements at can be formed by (i)
diagonal elements (unit matrix); (ii) and ; (iii)
and -block elements; (iv) -block elements. In the case of
unit matrix, both atmospheric and solar mixing angles and mass squared
differences are generated radiatively.Comment: 22 pages, 5 eps figures, JHEP3.cls, some clarifications and one
reference adde
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