Neutrinoless Double Beta Decay Matrix Research Articles

Investigation of pair-correlated 0+ states in Ba134 via the Ba136(p,t) reaction

We performed a high resolution study of ${0}^{+}$ states in $^{134}\mathrm{Ba}$ using the $^{136}\mathrm{Ba}(p,t)$ two-neutron transfer reaction. Our experiment shows a significant portion of the $L=0$ pair-transfer strength concentrated at excited ${0}^{+}$ levels in $^{134}\mathrm{Ba}$. Potential implications in the context of $^{136}\mathrm{Xe}\phantom{\rule{4pt}{0ex}}\ensuremath{\rightarrow}\phantom{\rule{4pt}{0ex}}^{136}\mathrm{Ba}$ neutrinoless double beta decay matrix element calculations are briefly discussed.

Neutrinoless double beta decay theory

Within left-right symmetric model a generalization of the Majorana neutrino mass for the case of light and and heavy neutrinos is introduced and analyzed. Further, current status of calculation of the neutrinoless double beta decay matrix elements is shortly reviewed. An important connection between them and matrix element of double Gamow-Teller operator is established. A new way of fixing quenching of axial-vector coupling constant gA is presented.

Relevance of the Nuclear Structure of the Stable Ge Isotopes to the Neutrino-less Double-Beta Decay of 76Ge

Gamma-ray detection following the inelastic neutron scattering reaction on isotopically enriched material was used to study the nuclear structure of 74Ge. From these measurements, low-lying, low-spin excited states were characterized, new states and their decays were identified, level lifetimes were measured with the Doppler-shift attenuation method (DSAM), multipole mixing ratios were established, and transition probabilities were determined. New structural features in 74Ge were identified, and the reanalysis of older 76Ge data led to the placement of the 2+ member of the intruder band. In addition, a number of previously placed states in 74Ge were shown not to exist. A procedure for future work, which will lead to meaningful data for constraining calculations of the neutrinoless double-beta decay matrix element, is suggested.

Comparison between variational Monte Carlo and shell model calculations of neutrinoless double beta decay matrix elements in light nuclei

Benchmark comparisons between many-body methods are performed to assess the ingredients necessary for an accurate calculation of neutrinoless double beta decay matrix elements. Shell model and variational Monte Carlo (VMC) calculations are carried out for A=10 and 12 nuclei. Different variational wavefunctions are used to evaluate the uncertainties in the ab initio calculations, finding fairly small differences between the VMC double beta decay matrix elements. For shell model calculations, the role of model space truncation, radial wavefunction choices, and short-range correlation are investigated and all found to be important. Based on the detailed comparisons between the VMC and shell model approaches, we conclude that accurate descriptions of neutrinoless double beta decay matrix elements require a proper treatment of both long-range and short-range correlations.

Neutrinoless double- β decay matrix elements in light nuclei

We present the first ab initio calculations of neutrinoless double beta decay matrix elements in $A=6$-$12$ nuclei using Variational Monte Carlo wave functions obtained from the Argonne $v_{18}$ two-nucleon potential and Illinois-7 three-nucleon interaction. We study both light Majorana neutrino exchange and potentials arising from a large class of multi-TeV mechanisms of lepton number violation. Our results provide benchmarks to be used in testing many-body methods that can be extended to the heavy nuclei of experimental interest. In light nuclei we have also studied the impact of two-body short range correlations and the use of different forms for the transition operators, such as those corresponding to different orders in chiral effective theory.

Large θ 13 in a SUSY SU(5) × T′ model

In the model based on SUSY SU(5) combined with the T' family symmetry, it is shown in Phys. Lett. B 652, 34 (2007) and Phys. Lett. B 681, 444 (2009) that fermion mass hierarchy and mixing angles can be naturally generated in both lepton and quark sectors compatible with various experimental measurements. But the predicted value for the non-zero lepton mixing angle of \theta_13 \simeq \theta_c/3\sqrt{2} contradicts the recent experimental results from Daya Bay and RENO. We propose to introduce one more singlet flavon field in the neutrino sector, and with its additional contribution, we are able to generate the large mixing angle \theta_13 ~ 8^{\circ}-10^{\circ}. The analytical expressions of the mixing angles and neutrino masses with the additional flavon field are derived. Our numerical results show that a large region in the model parameter space is allowed for the normal hierarchy case, while a much smaller region is allowed for the inverted hierarchy case. In addition, the predicted value of the solar mixing angle is not affected by the additional singlet contribution. On the other hand, there exists a correlation between \theta_13 value and \theta_23 - \pi/4, as a result of the additional singlet contribution. We also make predictions for various other variables that can be potentially tested in the future neutrino experiments such as the Dirac CP phase, which is predicted to be in the range of \delta ~ (195^{\circ}-200^{\circ}), and the neutrinoless double beta decay matrix element, <m_\beta\beta>. One numerical example with the minimal \chi^2 fit is presented, and the model predictions are consistent with all experimental results.

The QRPA study of neutrinoless double beta decay with and without proton-neutron pairing

We have examined the role of proton-neutron pairing on the Quasiparticle Random Phase Approximation (QRPA) by calculating neutrinoless double beta decay matrix elements using the recently proposed full-QRPA, which includes proton-neutron pairing. With this full-QRPA we have performed calculations on the neutrinoless double beta decay matrix elements of the experimentally interesting nuclei A=48, 76, 82, 96, 100, 116, 128, 130 and 136. Using the best presently available experimental limits on the half-time of neutrinoless double beta decay we have extracted new limits on the lepton number violating parameters. We have found that the inclusion of proton-neutron pairing makes the limits on the lepton number non-conserving parameters less stringent.

Neutrinoless double beta decay within the quasiparticle random-phase approximation 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 lifetime of neutrinoless double beta decay we have extracted the limits on lepton number violating parameters. \textcopyright{} 1996 The American Physical Society.

Neutrinoless double beta decay matrix elements beyond closure approximation

The nuclear matrix elements of all operators entering 0ν ββ-decay beyond closure approximation have been calculated in the case of A = 48. Within the 0 f 7 2 model we find that the closure approximation is quite good. The various intermediate states contribute additively. The retardation of the usual matrix elements can be traced to the reduced matrix elements connecting the intermediate states to the final. The matrix elements associated with heavy neutrinos and the recoil term are not retarded.