237 research outputs found
Neutrinoless double beta decay within Self-consistent Renormalized Quasiparticle Random Phase Approximation and inclusion of induced nucleon currents
The first, to our knowledge, calculation of neutrinoless double beta decay
(-decay) matrix elements within the self-consistent
renormalised Quasiparticle Random Phase Approximation (SRQRPA) is presented.
The contribution from the momentum-dependent induced nucleon currents to
-decay amplitude is taken into account. A detailed nuclear
structure study includes the discussion of the sensitivity of the obtained
SRQRPA results for -decay of Ge to the parameters of
nuclear Hamiltonian, two-nucleon short-range correlations and the truncation of
the model space. A comparision with the standard and renormalized QRPA is
presented. We have found a considerable reduction of the SRQRPA nuclear matrix
elements, resulting in less stringent limits for the effective neutrino mass.Comment: 13 pages, 3 figures, 1 tabl
A deformed QRPA formalism for single and two-neutrino double beta decay
We use a deformed QRPA formalism to describe simultaneously the energy
distributions of the single beta Gamow-Teller strength and the two-neutrino
double beta decay matrix elements. Calculations are performed in a series of
double beta decay partners with A = 48, 76, 82, 96, 100, 116, 128, 130, 136 and
150, using deformed Woods-Saxon potentials and deformed Skyrme Hartree-Fock
mean fields. The formalism includes a quasiparticle deformed basis and residual
spin-isospin forces in the particle-hole and particle-particle channels. We
discuss the sensitivity of the parent and daughter Gamow-Teller strength
distributions in single beta decay, as well as the sensitivity of the double
beta decay matrix elements to the deformed mean field and to the residual
interactions. Nuclear deformation is found to be a mechanism of suppression of
the two-neutrino double beta decay. The double beta decay matrix elements are
found to have maximum values for about equal deformations of parent and
daughter nuclei. They decrease rapidly when differences in deformations
increase. We remark the importance of a proper simultaneous description of both
double beta decay and single Gamow-Teller strength distributions. Finally, we
conclude that for further progress in the field it would be useful to improve
and complete the experimental information on the studied Gamow-Teller strengths
and nuclear deformations.Comment: 33 pages, 19 figures. To be published in Phys. Rev.
Uncertainty in the 0νββ decay nuclear matrix elements
The nuclear matrix elements M0nu of the neutrinoless double-beta decay (0nubetabeta) are evaluated for 76Ge,100Mo,130Te, and 136Xe within the renormalized quasiparticle random phase approximation (RQRPA) and the simple QRPA. Three sets of single particle level schemes are used, ranging in size from 9 to 23 orbits. When the strength of the particle-particle interaction is adjusted so that the 2nubetabeta decay rate is correctly reproduced, the resulting M0nu values become essentially independent of the size of the basis, and of the form of different realistic nucleon-nucleon potentials. Thus, one of the main reasons for variability of the calculated M0nu within these methods is eliminated
Effect of deformation on two-neutrino double beta decay matrix elements
We study the effect of deformation on the two-neutrino double beta decay for
ground state to ground state transitions in all the nuclei whose half-lives
have been measured. Our theoretical framework is a deformed QRPA based in
Woods-Saxon or Hartree-Fock mean fields. We are able to reproduce at the same
time the main characteristics of the two single beta branches, as well as the
double beta matrix elements. We find a suppression of the double beta matrix
element with respect to the spherical case when the parent and daughter nuclei
have different deformations
Erratum: Assessment of uncertainties in QRPA -decay nuclear matrix elements [Nucl. Phys. A 766, 107 (2006)]
This is an erratum to our previously published paper.Comment: Accepted for publication in Nucl. Phys. A, see also nucl-th/050306
Nuclear matrix elements for neutrinoless double-beta decay and double-electron capture
A new generation of neutrinoless double beta decay experiments with improved
sensitivity is currently under design and construction. They will probe
inverted hierarchy region of the neutrino mass pattern. There is also a revived
interest to the resonant neutrinoless double-electron capture, which has also a
potential to probe lepton number conservation and to investigate the neutrino
nature and mass scale. The primary concern are the nuclear matrix elements.
Clearly, the accuracy of the determination of the effective Majorana neutrino
mass from the measured 0\nu\beta\beta-decay half-life is mainly determined by
our knowledge of the nuclear matrix elements. We review recent progress
achieved in the calculation of 0\nu\beta\beta and 0\nu ECEC nuclear matrix
elements within the quasiparticle random phase approximation. A considered
self-consistent approach allow to derive the pairing, residual interactions and
the two-nucleon short-range correlations from the same modern realistic
nucleon-nucleon potentials. The effect of nuclear deformation is taken into
account. A possibility to evaluate 0\nu\beta\beta-decay matrix elements
phenomenologically is discussed.Comment: 24 pages; 80 references. arXiv admin note: substantial text overlap
with arXiv:1101.214
Two-neutrino double beta decay of deformed nuclei within QRPA with realistic interaction
A method to implement realistic nucleon-nucleon residual interaction (Bonn CD
force) based on the Brueckner G-matrix into the Quasiparticle Random Phase
Approximation (QRPA) for deformed nuclei is formulated. The two-neutrino double
decay for ground state to ground state transitions GeSe and
Nd Sm is calculated along with the Gamow-Teller strength
distributions. The effect of deformation on the observables is studied.Comment: 18 pages, 6 figures, accepted for publication in in Phys. Rev.
Chiral two-body currents and neutrinoless double-β decay in the quasiparticle random-phase approximation
We test the effects of an approximate treatment of two-body contributions to the axial-vector current on the quasiparticle random-phase approximation (QRPA) matrix elements for neutrinoless double-beta decay in a range of isotopes. The form and strength of the two-body terms come from chiral effective-field theory. The two-body currents typically reduce the matrix elements by about 20%, not as much as in shell-model calculations. One reason for the difference is that standard practice in the QRPA is to adjust the strength of the isoscalar pairing interaction to reproduce two-neutrino double-beta decay lifetimes. Another may be the larger QRPA single-particle space. Whatever the reasons, the effects on neutrinoless decay are significantly less than those on two-neutrino decay, both in the shell model and the QRPA
Searching for New Physics in Two-Neutrino Double Beta Decay
Motivated by non-zero neutrino masses and the possibility of New Physics
discovery, a number of experiments search for neutrinoless double beta decay.
While hunting for this hypothetical nuclear process, a significant amount of
two-neutrino double beta decay data has become available. Although these events
are regarded and studied mostly as the background of neutrinoless double beta
decay, they can be also used to probe physics beyond the Standard Model. In
this paper we show how the presence of right-handed leptonic currents would
affect the energy distribution and angular correlation of the outgoing
electrons in two-neutrino double beta decay. Consequently, we estimate
constraints imposed by currently available data on the existence of
right-handed neutrino interactions without having to assume their nature. In
this way our results complement the bounds coming from the non-observation of
neutrinoless double beta decay as they limit also the exotic interactions of
Dirac neutrinos. We perform a detailed calculation of two-neutrino double beta
decay under the presence of exotic (axial-)vector currents and we demonstrate
that current experimental searches can be competitive to existing limits.Comment: 28 pages, 6 figures, including appendi
The 0nbb-decay nuclear matrix elements with self-consistent short-range correlations
A self-consistent calculation of nuclear matrix elements of the neutrinoless
double beta decays (0nbb) of 76Ge, 82Se, 96Zr, 100Mo, 116Cd, 128Te, 130Te and
130Xe is presented in the framework of the renormalized quasiparticle random
phase approximation (RQRPA) and the standard QRPA. The pairing and residual
interactions as well as the two-nucleon short-range correlations are for the
first time derived from the same modern realistic nucleon-nucleon potentials,
namely from charge-dependent Bonn potential (CD-Bonn) and the Argonne V18
potential. In a comparison with the traditional approach of using the
Miller-Spencer Jastrow correlations matrix elements for the 0nbb-decay are
obtained, which are larger in magnitude. We analyze the differences among
various two-nucleon correlations including those of the unitary correlation
operator method (UCOM) and quantify the uncertainties in the calculated
0nbb-decay matrix elements.Comment: 11 pages, 5 figure
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