Nuclear Matrix Elements of Double Beta Decay in Deformed Nuclei (original) (raw)
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Two neutrino double-β decay in deformed nuclei with an angular momentum projected basis
Physical Review C, 2004
Four nuclei which are proved to be 2νββ emitters ( 76 Ge, 82 Se, 150 Nd, 238 U), and four suspected, due to the corresponding Q-values, to have this property ( 148 Nd, 154 Sm, 160 Gd, 232 Th), were treated within a proton-neutron quasiparticle random phase approximation (pnQRPA) with a projected spherical single particle basis. The advantage of the present procedure over the ones using a deformed Woods Saxon or Nilsson single particle basis is that the actual pnQRPA states have a definite angular momentum while all the others provide states having only K as a good quantum number. The model Hamiltonian involves a mean field term yielding the projected single particle states, a pairing interaction for alike nucleons and a dipole-dipole proton-neutron interaction in both the particle-hole (ph) and particle-particle (pp) channels. The effect of nuclear deformation on the single beta strength distribution as well as on the double beta Gamow-Teller transition amplitude (M GT ) is analyzed. The results are compared with the existent data and with the results from a different approach, in terms of the process half life T 1/2 . The case of different deformations for mother and daughter nuclei is also presented.
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.
Physical Review C, 2005
Using an angular momentum projected single particle basis, a pnQRPA approach is used to study the 2νββ properties of ten isotopes, exhibiting various quadrupole deformations. The mother and daughter nuclei exhibit different quadrupole deformations. Since the projected basis enables a unified description of deformed and spherical nuclei, situations where the nuclei involved in the double beta decay process are both spherical, both deformed or one spherical and another deformed, can be treated through a sole formalism. Dependence of single β − and β + strength distribution on atomic mass number and nuclear deformation is analyzed. For the double beta decay process, the Gamow-Teller transition amplitudes and half lives are calculated. Results are compared with the experimental data as well as with the predictions of other theoretical approaches. The agreement between the present results and experimental data is fairly good.
Relativistic description of nuclear matrix elements in neutrinoless double-β decay
Neutrinoless double-beta (0νββ) decay is related to many fundamental concepts in nuclear and particle physics beyond the Standard Model. We report the first full relativistic description of the nuclear matrix element (NME) governing this process by multi-reference covariant density functional theory (MR-CDFT) based on the point-coupling functional PC-PK1. The dynamic correlations are taken into account by configuration mixing of both particle number and angular momentum projected quadrupole deformed mean-field states for the initial and final nuclei. The 0νββ NMEs for both the 0 + 1 → 0 + 1 and 0 + 1 → 0 + 2 decays in 150 Nd are evaluated. The effects of particle number projection, and static and dynamic deformations on the nuclear wave functions, as well as those of the full relativistic structure of the transition operator on the NMEs are studied in detail. The low-energy spectra and electric quadrupole transitions are well reproduced by the full generator coordinate method (GCM) calculation. The resulting NME for the 0 + 1 → 0 + 1 transition is 5.60, which gives the most optimistic prediction for the next generation of experiments searching for the 0νββ decay in 150 Nd.
Neutrinoless double beta decay in heavy deformed nuclei
Nuclear Physics A, 1995
The zero neutrino mode of the double beta decay in heavy deformed nuclei is investigated in the framework of the pseudo SU(3) model, which has provided an accurate description of collective nuclear structure and predicted half-lives for the two neutrino mode in good agreement with experiments. In the case of 238 U the calculated zero neutrino half-life is at least three orders of magnitude greater than the two neutrino one, giving strong support of the identification of the radiochemically determined half-life as being the two neutrino double beta decay. For 150 N d the zero neutrino matrix elements are of the order of magnitude of, but lesser than, those evaluated using the QRPA. This result confirms that different nuclear models produce similar zero neutrino matrix elements, contrary to the two neutrino case. Using these pseudo SU(3) results and the upper limit for the neutrino mass we estimate the ββ 0ν half-lives for six nuclei.
Spin-dipole nuclear matrix elements for double beta decays and astro-neutrinos
Physics Letters B
Spin-dipole (SD) nuclear matrix elements (NMEs) M±(SD2)M±(SD2) for unique first forbidden β±2−→0+ ground-state-to-ground-state transitions are studied by using effective microscopic two-nucleon interactions in realistic single-particle model spaces. The observed values of the NMEs Mexp±(SD2) are compared with the values of the single-quasiparticle NMEs Mqp±(SD2) without nucleon spin–isospin (στ) correlation and the QRPA NMEs MQRPA±(SD2) with the στ correlation. The observed SD matrix elements are found to be reduced by the factor k≈0.2k≈0.2 with respect to Mqp±(SD2) and by the factor kNM≈0.5kNM≈0.5 with respect to MQRPA±(SD2). We then infer that the SD NME is reduced considerably partly by the nucleon στ correlations and partly by other non-nucleonic and nucleonic correlations which are not explicitly included in the QRPA. Impact of the found reduction factors on the magnitudes of the NMEs involved in neutrino-less double beta decays and astro-neutrino interactions are discussed.
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 ...
Acta Physica Polonica B
The knowledge of the nuclear matrix elements (NME) for the neutrinoless double beta decay is fundamental for neutrino physics. The NMEs indeed enter in the expression connecting the half-life of the neutrinoless double beta decay to the neutrino mass. Information on the nuclear matrix elements can be obtained by measuring the cross section of double charge exchange nuclear reactions. The basic point is that the initial and final-state wave functions in the two processes are the same and the transition operators are similar. The double charge exchange cross sections can be factorized in a nuclear structure term containing the matrix elements and a nuclear reaction factor. First pioneering experimental results for the 40 Ca(18 O, 18 Ne) 40 Ar reaction at 270 MeV incident energy show that such cross section factorization reasonably holds for the 0 + to 0 + transition to the 40 Ar gs , at least at very forward angles.
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.