Half-life Of Double Beta Decay Research Articles

Calculation of two-neutrino double beta decay half-lives of 76Ge, 82Se, 96Zr and 100Mo nuclei for the 0+ → 0+ transition

We calculated the half-lives of two-neutrino double beta decay of 76Ge, 82Se, 96Zr and 100Mo nuclei for the 0+ ↦ 0+ transition. Quasiparticle random phase approximation (QRPA) was used by considering the charge-exchange spin–spin interactions among the nucleons by considering both particle–hole (p–h) and particle–particle (p–p) channels in the separable form. Calculations were performed for the spherical form of the nuclei.

CUORE and Beyond: Bolometric Techniques to Explore Inverted Neutrino Mass Hierarchy

The CUORE (Cryogenic Underground Observatory for Rare Events) experiment will search for neutrinoless double beta decay of 130Te. With 741kg of TeO2 crystals and an excellent energy resolution of 5 keV (0.2%) at the region of interest, CUORE will be one of the most competitive neutrinoless double beta decay experiments on the horizon. With five years of live time, CUORE projected neutrinoless double beta decay half-life sensitivity is 1.6 × 1026 y at 1σ (9.5 × 1025 y at the 90% confidence level), which corresponds to an upper limit on the effective Majorana mass in the range 40–100 meV (50–130 meV). Further background rejection with auxiliary light detector can significantly improve the search sensitivity and competitiveness of bolometric detectors to fully explore the inverted neutrino mass hierarchy with 130Te and possibly other double beta decay candidate nuclei.

A flexible scintillation light apparatus for rare event searches

Compelling experimental evidences of neutrino oscillations and their implication that neutrinos are massive particles have given neutrinoless double beta decay a central role in astroparticle physics. In fact, the discovery of this elusive decay would be a major breakthrough, unveiling that neutrino and antineutrino are the same particle and that the lepton number is not conserved. It would also impact our efforts to establish the absolute neutrino mass scale and, ultimately, understand elementary particle interaction unification. All current experimental programs to search for neutrinoless double beta decay are facing with the technical and financial challenge of increasing the experimental mass while maintaining incredibly low levels of spurious background. The new concept described in this paper could be the answer which combines all the features of an ideal experiment: energy resolution, low cost mass scalability, isotope choice flexibility and many powerful handles to make the background negligible. The proposed technology is based on the use of arrays of silicon detectors cooled to 120 K to optimize the collection of the scintillation light emitted by ultra-pure crystals. It is shown that with a 54 kg array of natural CaMoO4 scintillation detectors of this type it is possible to yield a competitive sensitivity on the half-life of the neutrinoless double beta decay of 100Mo as high as ~10E24 years in only one year of data taking. The same array made of 40CaMoO4 scintillation detectors (to get rid of the continuous background coming from the two neutrino double beta decay of 48Ca) will instead be capable of achieving the remarkable sensitivity of ~10E25 years on the half-life of 100Mo neutrinoless double beta decay in only one year of measurement.

Status of double beta decay experiments using isotopes other than 136 Xe

Neutrinoless double beta decay is a lepton-number violating process predicted by many extensions of the standard model. It is actively searched for in several candidate isotopes within many experimental projects. The status of the experimental initiatives which are looking for the neutrinoless double beta decay in isotopes other than Xe-136 is reviewed, with special emphasis given to the projects that passed the R&D phase. The results recently released by the experiment GERDA are also summarized and discussed. The GERDA data give no positive indication of neutrinoless double beta decay of Ge-76 and disfavor in a model-independent way the long-standing observation claim on the same isotope. The lower limit reported by GERDA for the half-life of neutrinoless double beta decay of Ge-76 is T1/2 > 2.1e25 yr (90% C.L.), or T1/2 > 3.0e25 yr, when combined with the results of other Ge-76 predecessor experiments.

Remark on Majorana CP phases in neutrino mixing and leptogenesis

We estimate Majorana CP phases for a simple flavor neutrino mixing matrix which has been reported by Qu and Ma. Sizes of Majorana CP phases are evaluated in the study of the neutrinoless double beta decay and a particular leptogenesis scenario. We find the dependence of the physically relevant Majorana CP phase on the mass of lightest right-handed neutrino in the minimal seesaw model and the effective Majorana neutrino mass which is related with the half-life of the neutrinoless double beta decay.

Quasi Random Phase Approximation Predictions on Two-Neutrino Double Beta Decay Half-Lives to the First 2+ State

Two-neutrino double beta decay (2νββ) half-lives to the first excited state are calculated in the framework of quasi random phase approximation. The quadrupole transition probabilities and the 2νββ decay amplitudes to the final ground states are reproduced by using adjustable parameters. The obtained half-lives are compared with the corresponding experimental data.

Deformed shell model studies of spectroscopic properties of 64Zn and 64Ni and the positron double beta decay of 64Zn

The spectroscopic properties of 64Zn and 64Ni are calculated within the framework of the deformed shell model (DSM) based on Hartree-Fock states. GXPF1A interaction in 1f7/2, 2p3/2, 1f5/2 and 2p1/2 space with 40Ca as the core is employed. After ensuring that DSM gives good description of the spectroscopic properties of low-lying levels in these two nuclei considered, nuclear transition matrix elements (NTME) for the neutrinoless positron double beta decay ( 0νβ+β+ and 0νβ+EC) of 64Zn are calculated. The two-neutrino positron double beta decay half-life is also calculated for this nucleus.

Investigation of double beta decay of 100Mo to excited states of 100Ru

Double beta decay of $^{100}$Mo to the excited states of daughter nuclei has been studied using a 600 cm$^3$ low-background HPGe detector and an external source consisting of 2588 g of 97.5% enriched metallic $^{100}$Mo, which was formerly inside the NEMO-3 detector and used for the NEMO-3 measurements of $^{100}$Mo. The half-life for the two-neutrino double beta decay of $^{100}$Mo to the excited 0$^+_1$ state in $^{100}$Ru is measured to be $T_{1/2}=[7.5 \pm{0.6}(stat) \pm {0.6}(syst)]\cdot 10^{20}$ yr. For other $(0\nu + 2\nu)$ transitions to the 2$^+_1$, 2$^+_2$, 0$^+_2$, 2$^+_3$ and 0$^+_3$ levels in $^{100}$Ru, limits are obtained at the level of $\sim (0.25-1.1)\cdot 10^{22}$ yr.

Novel Approaches to Calculate Nuclear Matrix Elements for Double Beta Decays

Neutrinoless double beta decay is a unique process that could reveal physics beyond the Standard Model of particle physics. If observed, it would prove that neutrinos are Majorana particles, and it could give information regarding the neutrino masses and their hierarchy, provided that reliable nuclear matrix elements (NME) can be obtained. The two-neutrino double beta decay is an associate process that is allowed by the Standard Model and it was observed for about ten nuclei. The NME associated with this decay mode could be even more difficult to calculate, but they can be directly related to the experimental half-lives, and they can be constrained using data from charge-exchange reactions. Here we offer a brief overview of the theoretical challenges associated with these two processes, emphasizing the tools necessary to reliably calculate the associated nuclear matrix elements. We also emphasize the role of the competing mechanisms that could contribute to the neutrinoless double beta decay half-life.

Results on Neutrinoless Double-βDecay ofGe76from Phase I of the GERDA Experiment

Neutrinoless double beta decay is a process that violates lepton number conservation. It is predicted to occur in extensions of the standard model of particle physics. This Letter reports the results from phase I of the Germanium Detector Array (GERDA) experiment at the Gran Sasso Laboratory (Italy) searching for neutrinoless double beta decay of the isotope (76)Ge. Data considered in the present analysis have been collected between November 2011 and May 2013 with a total exposure of 21.6 kg yr. A blind analysis is performed. The background index is about 1 × 10(-2) counts/(keV kg yr) after pulse shape discrimination. No signal is observed and a lower limit is derived for the half-life of neutrinoless double beta decay of (76)Ge, T(1/2)(0ν) >2.1 × 10(25) yr (90% C.L.). The combination with the results from the previous experiments with (76)Ge yields T(1/2)(0ν)>3.0 × 10(25) yr (90% C.L.).

Lepton number and flavour violation in TeV-scale left-right symmetric theories with large left-right mixing

The various diagrams leading to neutrinoless double beta decay in the left-right symmetric model have different relative magnitudes, depending on the scale of new physics. Neutrinos acquire mass from both type I and/or type II seesaw terms, making an unambiguous analysis difficult. We study the half-life for double beta decay in the case of type II and type I dominance, in the former case including interference terms. If the heavy neutrinos of the type I seesaw model are at the TeV scale, certain processes can be enhanced. In particular, there are regions of parameter space in which the so-called lambda- and eta-diagrams can give sizable contributions to the half-life for the decay. We perform a detailed study of one such scenario, paying careful attention to constraints from lepton flavour violation.

Shell-Model Analysis of theXe136Double Beta Decay Nuclear Matrix Elements

Neutrinoless double beta decay, if observed, could distinguish whether neutrino is a Dirac or a Majorana particle, and it could be used to determine the absolute scale of the neutrino masses. $^{136}$Xe is one of the most promising candidates for observing this rare event. However, until recently there were no positive result for the allowed and less rare two-neutrino double beta decay mode. The small nuclear matrix element associated with the small half-life represents a challenge for nuclear structure models used for its calculation. We report a new shell-model analysis of the two-neutrino double beta decay of $^{136}$Xe, which takes into account all relevant nuclear orbitals necessary to fully describe the associated Gamow-Teller strength. We further use the new model to analyze the main contributions to the neutrinoless double beta decay half-life, and show that they are also diminished.

Quasi-random phase approximation analysis of two-neutrino double-beta decay to the first 2+ state of 128,130Xe isotopes

Quasi-random phase approximation analysis of the two-neutrino double-beta decay to the first 2+ state of 128,130Xe isotopes is presented in this work. The wave functions of the first 2+ state have been obtained within the charge-conserving quasiparticle randsom phase approximation (QRPA) ((pp + nn)QRPA) with the effective interactions in the particle–hole and particle–particle channels. The intermediate states have been calculated within the charge-exchange QRPA proton–neutron QRPA (pnQRPA). The stability of the nuclear matrix element for the two-neutrino double-beta decay to the first 2+ state has been studied by calculating its dependence on the strength parameter of the particle–particle interaction in the pnQRPA calculations and the double-beta decay half-lives have been calculated. The obtained results have been compared with the corresponding experimental data.

Measurement of the half-life of the two-neutrino double beta decay of 76Ge with the GERDA experiment

The primary goal of the GERmanium Detector Array (GERDA) experiment at the Laboratori Nazionali del Gran Sasso of INFN is the search for the neutrinoless double beta decay of 76Ge. High-purity germanium detectors made from material enriched in 76Ge are operated directly immersed in liquid argon, allowing for a substantial reduction of the background with respect to predecessor experiments. The first 5.04 kg yr of data collected in Phase I of the experiment have been analyzed to measure the half-life of the neutrino-accompanied double beta decay of 76Ge. The observed spectrum in the energy range between 600 and 1800 keV is dominated by the double beta decay of 76Ge. The half-life extracted from GERDA data is T2ν1/2 = (1.84+0.14−0.10) × 1021 yr.

Limit on NeutrinolessββDecay ofXe136from the First Phase of KamLAND-Zen and Comparison with the Positive Claim inGe76

We present results from the first phase of the KamLAND-Zen double-beta decay experiment, corresponding to an exposure of 89.5 kg yr of (136)Xe. We obtain a lower limit for the neutrinoless double-beta decay half-life of T(1/2)(0ν)>1.9×10(25) yr at 90% C.L. The combined results from KamLAND-Zen and EXO-200 give T(1/2)(0ν)>3.4×10(25) yr at 90% C.L., which corresponds to a Majorana neutrino mass limit of <m(ββ)> <(120-250) meV based on a representative range of available matrix element calculations. Using those calculations, this result excludes the Majorana neutrino mass range expected from the neutrinoless double-beta decay detection claim in (76)Ge, reported by a part of the Heidelberg-Moscow Collaboration, at more than 97.5% C.L.

Measurement of the double-βdecay half-life of136Xe with the KamLAND-Zen experiment

We present results from the KamLAND-Zen double-beta decay experiment based on an exposure of 77.6 days with 129 kg of $^{136}$Xe. The measured two-neutrino double-beta decay half-life of $^{136}$Xe is $T_{1/2}^{2\nu} = 2.38 \pm 0.02(stat) \pm 0.14(syst) \times 10^{21}$ yr, consistent with a recent measurement by EXO-200. We also obtain a lower limit for the neutrinoless double-beta decay half-life, $T_{1/2}^{0\nu} > 5.7 \times 10^{24}$ yr at 90% confidence level (C.L.), which corresponds to almost a five-fold improvement over previous limits.

The search for neutrinoless double beta decay with Cuoricino and Cuore

Cuoricino was a cryogenic bolometric detector operating in Gran Sasso Underground Laboratory, Italy, from March 2003 to June 2008. With its 40.7 kg of 130TeO2 in the form of an array of 62 crystals it has set the currently best lower limit on the halflife of 130Te neutrinoless double beta decay, T1/2 > 2.94 · 1024 y at 90 % CL. It has moreover proven the feasibility of the CUORE experiment, whose aim is to be sensitive to values of the effective neutrino mass as low as few tens of meV. We will report on the latest results from Cuoricino and on the status of the CUORE project.

NEUTRINO-LESS DOUBLE BETA DECAY AND PARTICLE PHYSICS

We review the particle physics aspects of neutrino-less double beta decay. This process can be mediated by light massive Majorana neutrinos (standard interpretation) or by something else (non-standard interpretations). The physics potential of both interpretations is summarized and the consequences of future measurements or improved limits on the half-life of neutrino-less double beta decay are discussed. We try to cover all proposed alternative realizations of the decay, including light sterile neutrinos, supersymmetric or left-right symmetric theories, Majorons, and other exotic possibilities. Ways to distinguish the mechanisms from one another are discussed. Experimental and nuclear physics aspects are also briefly touched, alternative processes to double beta decay are discussed, and an extensive list of references is provided.

Search for double beta decay with the EXO-200 TPC and prospects for barium ion tagging in liquid xenon

Neutrino oscillation experiments have shown that neutrinos have very small but non vanishing masses. These experiments are not able to determine neither the absolute mass scale of neutrinos nor whether they are Majorana particles. Neutrino-less double beta decay can only occur if the neutrinos are Majorana particles, a preferred scenario in most possible schemes leading to finite masses. Among several viable candidate isotopes, EXO has chosen Xe-136. The final state (i.e. the barium ion) can be tagged using optical spectroscopy. The efficient detection of the double beta decay daughter nucleus is a key step toward a background free measurement of such a rare process. An intermediate size detector (EXO-200) of 200 kg enriched xenon has been installed underground at WIPP (US). It is an ultra-low background detector with a design sensitivity of 6 × 1025 years for the half-life of neutrino-less double beta decay in Xe-136. A larger, ton-scale experiment is being designed with Ba ion tagging capability. We are presenting the status of the EXO-200 detector and review the R&D activities for a ton-scale EXO detector with barium ion tagging.

Double-beta decay Q values of 116Cd and 130Te

The Q values of the 116Cd and 130Te double-beta decaying nuclei were determined by using a Penning trap mass spectrometer. The new atomic mass difference between 116Cd and 116Sn of 2813.50(13) keV differs by 4.5 keV and is 30 times more precise than the previous value of 2809(4) keV. The new value for 130Te, 2526.97(23) keV is close to the Canadian Penning trap value of 2527.01±0.32 keV (Scielzo et al., 2009) [1], but differs from the Florida State University trap value of 2527.518±0.013 keV (Redshaw et al., 2009) [2] by 0.55 keV (2σ). These values are sufficiently precise for ongoing neutrinoless double-beta decay searches in 116Cd and 130Te. Hence, our Q values were used to compute accurate phase-space integrals for these double-beta decay nuclei. In addition, experimental two-neutrino double-beta decay nuclear matrix elements were determined and compared with the theoretical values. The neutrinoless double-beta decay half-lives for these nuclei were estimated using our precise phase-space integrals and considering the range of the best available matrix elements values.