193 research outputs found
Constraints on light neutrino parameters derived from the study of neutrinoless double beta decay
The study of the neutrinoless double beta () decay mode can
provide us with important information on the neutrino properties, particularly
on the electron neutrino absolute mass. In this work we revise the present
constraints on the neutrino mass parameters derived from the
decay analysis of the experimentally interesting nuclei. We use the latest
results for the phase space factors (PSFs) and nuclear matrix elements (NMEs),
as well as for the experimental lifetimes limits. For the PSFs we use values
computed with an improved method reported very recently. For the NMEs we use
values chosen from literature on a case-by-case basis, taking advantage of the
consensus reached by the community on several nuclear ingredients used in their
calculation. Thus, we try to restrict the range of spread of the NME values
calculated with different methods and, hence, to reduce the uncertainty in
deriving limits for the Majorana neutrino mass parameter. Our results may be
useful to have an up-date image on the present neutrino mass sensitivities
associated with measurements for different isotopes and to
better estimate the range of values of the neutrino masses that can be explored
in the future double beta decay (DBD) experiments.Comment: 11 page
Fast, Efficient Calculations of the Two-Body Matrix Elements of the Transition Operators for Neutrinoless Double Beta Decay
To extract information about the neutrino properties from the study of
neutrinoless double-beta (0\nu\beta\beta) decay one needs a precise computation
of the nuclear matrix elements (NMEs) associated with this process. Approaches
based on the Shell Model (ShM) are among the nuclear structure methods used for
their computation. ShM better incorporates the nucleon correlations, but have
to face the problem of the large model spaces and computational resources. The
goal is to develop a new, fast algorithm and the associated computing code for
efficient calculation of the two-body matrix elements (TBMEs) of the
0\nu\beta{\beta} decay transition operator, which are necessary to calculate
the NMEs. This would allow us to extend the ShM calculations for double-beta
decays to larger model spaces, of about 9-10 major harmonic oscillator shells.
The improvement of our code consists in a faster calculation of the radial
matrix elements. Their computation normally requires the numerical evaluation
of two-dimensional integrals: one over the coordinate space and the other over
the momentum space. By rearranging the expressions of the radial matrix
elements, the integration over the coordinate space can be performed
analytically, thus the computation reduces to sum up a small number of
integrals over momentum. Our results for the NMEs are in a good agreement with
similar results from literature, while we find a significant reduction of the
computation time for TBMEs, by a factor of about 30, as compared with our
previous code that uses two-dimensional integrals.Comment: 6 pages, one figur
Spin-Isospin Excitations and Muon Capture by Nuclei
By analyzing the energy-weighted moments of the strength function calculated
in RPA and beyond it is shown that the explanation of the effect of missing
strength of Gamow-Teller transitions requires that residual interaction produce
high-excited particle-hole collective states. The example of this
interaction is presented. The manifestations of spin-isospin nuclear response
in nuclear muon capture are discussed.Comment: 16 pages, 5 figures, 2 tables. The talk at the XVI International
School on Nuclear Physics, Neutron Physics and Nuclear Energy, September
19-26, Varna, Bulgari
Phase Space Factors for Double-Beta Decays
Double-beta decay is presently a very studied process both theoretically and experimentally due to its potential to provide valuable information about important, but still unknown issues related to the neutrino properties and conservation of some symmetries. In the theoretical study of the double-beta decay two key quantities entering the half-life formulas are important, namely the phase space factors embedding the influence of the Coulomb field of the daughter nucleus on the emitted electrons/positrons, and the nuclear matrix elements embedding the nuclear structure effects of the nuclei participating in the decay. Accurate calculation of both of them are needed for good predictions of the double-beta decay half-lives and transitions still unmeasured, and for constraining various beyond Standard Model parameters associated with mechanisms that may contribute to the neutrinoless double-beta decay modes. During time much attention has been paid to the nuclear matrix elements that were considered to bring the largest uncertainties in the computation of the double-beta decay half-lives, while the phase space factors were considered until the recent past to be computed with enough precision. However, newer computation of the phase space factors performed with more precise methods revealed relevant deviations from their values reported previously, especially for heavier nuclei and for positron emitting and electron capture decay modes. In this paper we review the progress made in the computation of the phase space factors for double beta decay. We begin with the non-relativistic approaches, continue with the relativistic approaches which use approximate electron/positron wave functions, and end up with recent, more precise, computations of the phase space factors where exact electron wave functions are obtained from the resolution of a Dirac equation in a Coulomb-type potential and with inclusion of finite nuclear size and screening effects. We report an up-dated and complete list of the phase space factors (PSF) for the following DBD modes: β−β−, β+β+, ECβ+, and ECEC and for transitions to final ground and first excited 2+ and 0+ states of the daughter nuclei. We also make a comparison between different values of the phase space factors found in literature and discuss the differences between these results
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