694 research outputs found
Nuclear moments for the neutrinoless double beta decay II
The recently developed formalism for the evaluation of nuclear form factors
in neutrinoless double beta decay is applied to , ,
, , and nuclei. Explicit analytical
expressions that follows from this theoretical development, in the single mode
model for the decay of , have been worked out. They are useful both
for testing the full numerical calculations, and for analytically checking the
consistency with other formalisms. Large configuration space calculations are
compared with previous studies, where alternative formulations were used. Yet,
besides using the G-matrix as residual interaction, we here use a simple
-force. Attention is paid to the connected effects of the short range
nuclear correlations and the finite nucleon size. Constraints on lepton number
violating terms in the weak Hamiltonian (effective neutrino Majorana mass and
effective right-handed current coupling strengths) are deduced.Comment: 18 pages, latex, minor changes, to appear in Nucl. Phys.
Exact evaluation of the nuclear form factor for new kinds of majoron emission in neutrinoless double beta decay
We have developed a formalism, based on the Fourier-Bessel expansion, that
facilitates the evaluation of matrix elements involving nucleon recoil
operators, such as appear in serveral exotic forms of neutrinoless double beta
decay (). The method is illustrated by applying it to the
``charged'' majoron model, which is one of the few that can hope to produce an
observable effect. From our numerical computations within the QRPA performed
for , , , and nuclei, we
test the validity of approximations made in earlier work to simplify the new
matrix elements, showing that they are accurate to within 15%. Our new method
is also suitable for computing other previously unevaluated
nuclear matrix elements.Comment: 11pp., latex, fixed minor typographical error
Shell Model Study of the Double Beta Decays of Ge, Se and Xe
The lifetimes for the double beta decays of Ge, Se and
Xe are calculated using very large shell model spaces. The two neutrino
matrix elements obtained are in good agreement with the present experimental
data. For eV we predict the following upper bounds to the
half-lives for the neutrinoless mode: , and . These results are the first from a new generation of Shell
Model calculations reaching O(10) dimensions
A New Class of Majoron-Emitting Double-Beta Decays
Motivated by the excess events that have recently been found near the
endpoints of the double beta decay spectra of several elements, we re-examine
models in which double beta decay can proceed through the neutrinoless emission
of massless Nambu-Goldstone bosons (majorons). Noting that models proposed to
date for this process must fine-tune either a scalar mass or a VEV to be less
than 10 keV, we introduce a new kind of majoron which avoids this difficulty by
carrying lepton number . We analyze in detail the requirements that
models of both the conventional and our new type must satisfy if they are to
account for the observed excess events. We find: (1) the electron sum-energy
spectrum can be used to distinguish the two classes of models from one another;
(2) the decay rate for the new models depends on different nuclear matrix
elements than for ordinary majorons; and (3) all models require a (pseudo)
Dirac neutrino, having a mass of a several hundred MeV, which mixes with
.Comment: 43 pages, 10 figures (included), [figure captions are now included
Neutrinoless Double Beta Decay within QRPA with Proton-Neutron Pairing
We have investigated the role of proton-neutron pairing in the context of the
Quasiparticle Random Phase approximation formalism. This way the neutrinoless
double beta decay matrix elements of the experimentally interesting A= 48, 76,
82, 96, 100, 116, 128, 130 and 136 systems have been calculated. We have found
that the inclusion of proton-neutron pairing influences the neutrinoless double
beta decay rates significantly, in all cases allowing for larger values of the
expectation value of light neutrino masses. Using the best presently available
experimental limits on the half life-time of neutrinoless double beta decay we
have extracted the limits on lepton number violating parameters.Comment: 16 RevTex page
The Single State Dominance Hypothesis and the Two-Neutrino Double Beta Decay of Mo100
The hypothesis of the single state dominance (SSD) in the calculation of the
two-neutrino double beta decay of Mo100 is tested by exact consideration of the
energy denominators of the perturbation theory. Both transitions to the ground
state as well as to the 0+ and 2+ excited states of the final nucleus Ru100 are
considered. We demonstrate, that by experimental investigation of the single
electron energy distribution and the angular correlation of the outgoing
electrons, the SSD hypothesis can be confirmed or ruled out by a precise
two-neutrino double beta decay measurement (e.g. by NEMO III collaboration).Comment: 13 pages, RevTex, 1 figur
Two neutrino double beta decay within the -approximation
We examine the contributions of odd-parity nuclear operators to the
two-neutrino double beta decay amplitude, which come from
the -wave Coulomb corrections to the electron wave functions and the recoil
corrections to the nuclear currents. Although they are formally of higher order
in or of the nucleon than the usual Fermi and Gamow-Teller
matrix elements, explicit calculations performed within the QRPA show that they
are significant when confronted with the experimental data.Comment: 9 pages, latex, no figure
Double beta decay of : the deformed limit
The double beta decay of to the ground state and excited states of
is analysed in the context of the pseudo SU(3) scheme. The results
of this deformed limit are compared with the vibrational one based on the QRPA
formalism. Consistency between the deformed limit and the experimental
information is found for various transitions, although, in this
approximation some energies and B(E2) intensities cannot reproduced.Comment: 16 pages, revtex, no figures. Submmitted to Phys. Rev.
CUORE: A Cryogenic Underground Observatory for Rare Events
CUORE is a proposed tightly packed array of 1000 TeO2 bolometers, each being
a cube 5 cm on a side with a mass of 760 g. The array consists of 25 vertical
towers, arranged in a square of 5 towers by 5 towers, each containing 10 layers
of 4 crystals. The design of the detector is optimized for ultralow-background
searches: for neutrinoless double beta decay of 130Te (33.8% abundance), cold
dark matter, solar axions, and rare nuclear decays. A preliminary experiment
involving 20 crystals 3x3x6 cm3 of 340 g has been completed, and a single CUORE
tower is being constructed as a smaller scale experiment called CUORICINO. The
expected performance and sensitivity, based on Monte Carlo simulations and
extrapolations of present results, are reported.Comment: 39 pages, 12 figures, submitted to NI
A Calorimetric Search on Double Beta Decay of 130Te
We report on the final results of a series of experiments on double decay of
130Te carried out with an array of twenty cryogenic detectors. The set-up is
made with crystals of TeO2 with a total mass of 6.8 kg, the largest operating
one for a cryogenic experiment. Four crystals are made with isotopically
enriched materials: two in 128Te and two others in 130Te. The remaining ones
are made with natural tellurium, which contains 31.7 % and 33.8 % 128Te and
130Te, respectively. The array was run under a heavy shield in the Gran Sasso
Underground Laboratory at a depth of about 3500 m.w.e. By recording the pulses
of each detector in anticoincidence with the others a lower limit of 2.1E23
years has been obtained at the 90 % C.L. on the lifetime for neutrinoless
double beta decay of 130Te. In terms of effective neutrino mass this is the
most restrictive limit in direct experiments, after those obtained with Ge
diodes. Limits on other lepton violating decays of 130Te and on the
neutrinoless double beta decay of 128Te to the ground state of 128Xe are also
reported and discussed. An indication is presented for the two neutrino double
beta decay of 130Te. Some consequences of the present results in the
interpretation of geochemical experiments are discussed.Comment: 14 pages, 3 figures, 2 tables; more analysis details. Accepted for
publication on Physics Letters
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