Neutron pair correlations in A=100 nuclei involved in neutrinoless double-β decay (original) (raw)
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Neutrinoless Double Beta Decay The Nuclear Matrix Elements Revisited
Journal of Physics: Conference Series, 2011
We explore the influence of the deformation on the nuclear matrix elements of the neutrinoless double beta decay (NME), concluding that the difference in deformation-or more generally in the amount of quadrupole correlations-between parent and grand daughter nuclei quenches strongly the decay. We correlate these differences with the seniority structure of the nuclear wave functions. In this context, we examine the present discrepancies between the NME's obtained in the framework of the Interacting Shell Model and the Quasiparticle RPA. In our view, part of the discrepancy can be due to the limitations of the spherical QRPA in treating nuclei which have strong quadrupole correlations. We surmise that the NME's in a basis of generalized seniority are approximately model independent, i. e. they are "universal". We discuss as well how varies the nuclear matrix element of the 76 Ge decay when the wave functions of the two nuclei involved in the transition are constrained to reproduce the experimental occupancies. In the Interacting Shell Model description the value of the NME is enhanced about 15% compared to previous calculations, whereas in the QRPA the NME's are reduced by 20%-30%. This diminishes the discrepancies between both approaches. In addition, we update the effects of the short range correlations on the NME's in the light of the recently proposed parametrizations obtained by renormalizing the 0νββ transition operator at the same footing than the effective interaction.
Studying Matrix Elements for the Neutrinoless Double Beta Decay of 150Nd via the
2008
The existence of neutrinoless double beta decay would prove that neutrinos have a Majorana nature and that lepton number is not conserved. To extract information about the neutrino mass scale and hierarchy from 0νβ β decay experimental data, accurate nuclear matrix elements are needed. Such information is also crucial for the design of experiments aimed at detecting neutrinoless double beta decay. Nuclear charge-exchange experiments play an important role in constraining the theories used to predict these matrix elements by providing Gamow-Teller strengths and higher order multipole transition strengths. The charge-exchange group at the NSCL focuses on the measurements of 150 Sm(t, 3 He) 150 Pm* and 150 Nd( 3 He,t) 150 Pm* reactions, which are of relevance for the double beta decay of 150 Nd. The details for the 150 Sm(t, 3 He) 150 Pm* experiment and the upcoming 150 Nd( 3 He,t) 150 Pm* experiment are discussed.
Universal features of the nuclear matrix elements governing the mass sector of the decay
Physics Letters B, 2005
In this work we report on manifest universal features found in the nuclear matrix elements which govern the mass sector of the neutrinoless double beta decay. The results are based on the analysis of the calculated matrix elements corresponding to the decays of 76Ge, 82Se, 100Mo, and 116Cd. The results suggest a dominance of few low-lying nuclear states of few multipoles in these matrix elements. Dedicated charge-exchange reactions could be used to probe these key states to determine experimentally the value of the nuclear matrix element.
Nuclear matrix elements for neutrinoless double-beta decay and double-electron capture
Journal of Physics G: Nuclear and Particle Physics, 2012
A new generation of neutrinoless double beta decay (0νββ-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 doubleelectron capture (0νECEC), 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 0νββ-decay half-life is mainly determined by our knowledge of the nuclear matrix elements. We review recent progress achieved in the calculation of 0νββ and 0νECEC 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 0νββ-decay matrix elements phenomenologically is discussed.
Study of nuclear effects in the computation of the 0νββ decay matrix elements
Journal of Physics G: Nuclear and Particle Physics, 2013
We analyze the effects that different nuclear structure approximations associated with the short range correlations (SRC), finite nucleon size (FNS), higher order terms in the nucleon currents (HOC) and with some nuclear input parameters, have on the values of the nuclear matrix elements (NMEs) for the neutrinoless double beta (0νββ) decay. The calculations are performed with a new Shell Model(ShM) code which allows a fast computation of the two-body matrix elements of the transition operators. The treatment of SRC, FNS and HOC and the use of quenched or unquenched values for the axial vector coupling constant produces the most important effects on the NMEs values. Equivalent effects of some of these approximations are also possible, which may lead (accidentally) to close final results. We found that the cumulative effect of all these nuclear ingredients on the calculated nuclear matrix elements NMEs is significant. Since the NMEs values are often obtained with different approximations and/or with different input parameters, a convergent view point on their inclusion/neglecting and an uniformization of the calculations are needed, in order to enter in an era of precision concerning the computation of the NMEs for double beta decay.
Mechanisms of neutrinoless double-beta decay: A comparative analysis of several nuclei
Physics of Atomic Nuclei, 2010
The neutrinoless double beta decay of several nuclei that are of interest from the experimental point of view ( 76 Ge, 82 Se, 100 Mo, 130 Te, and 136 Xe) is investigated on the basis of a general Lorentzinvariant effective Lagrangian describing physics effects beyond the Standard Model. The half-lives and angular-correlation coefficients for electrons are calculated for various decay mechanisms associated, in particular, with the exchange of Majorana neutrinos, supersymmetric particles (with R-parity violation), leptoquarks, and right-handed W R bosons. The effect of theoretical uncertainties in the values of relevant nuclear matrix elements on decay features is considered.
2016
We analyze the effects that different nuclear structure approximations associated with the short range correlations (SRC), finite nucleon size (FNS), higher order terms in the nucleon currents (HOC) and with some nuclear input parameters, have on the values of the nuclear matrix elements (NMEs) for the neutrinoless double beta (0νββ) decay. The calculations are performed with a new Shell Model(ShM) code which allows a fast computation of the two-body matrix elements of the transition operators. The treatment of SRC, FNS and HOC and the use of quenched or unquenched values for the axial vector coupling constant produces the most important effects on the NMEs values. Equivalent effects of some of these approximations are also possible, which may lead (accidentally) to close final results. We found that the cumulative effect of all these nuclear ingredients on the calculated nuclear matrix elements NMEs is significant. Since the NMEs values are often obtained with different approximations and/or with different input parameters, a convergent view point on their inclusion/neglecting and an uniformization of the calculations are needed, in order to enter in an era of precision concerning the computation of the NMEs for double beta decay.
Uncertainties in the 0νββ-decay nuclear matrix elements
Czechoslovak Journal of Physics, 2006
The nuclear matrix elements M 0ν of the neutrinoless double beta decay (0νββ) of most nuclei with known 2νββ-decay rates are systematically evaluated using the Quasiparticle Random Phase Approximation (QRPA) and Renormalized QRPA (RQRPA). The experimental 2νββ-decay rate is used to adjust the most relevant parameter, the strength of the particle-particle interaction. With such procedure the M 0ν values become essentially independent on single-particle basis size, the axial vector quenching factor, etc. Theoretical arguments in favor of the adopted way of determining the interaction parameters are presented. It is suggested that most of the spread among the published M 0ν 's can be ascribed to the choices of implicit and explicit parameters, inherent to the QRPA method.
Anatomy of nuclear matrix elements for neutrinoless double-beta decay
Arxiv preprint arXiv: …, 2007
Abstract: We show that, within the Quasiparticle Random Phase Approximation (QRPA) and the renormalized QRPA (RQRPA) based on the Bonn CD nucleon-nucleon interaction, the competition between the pairing and the neutron-proton particle-particle and particle-hole ...