Future Double Beta Decay Experiments Research Articles

Neutrino masses and mass hierarchy: evidence for the normal hierarchy

The latest cosmological constraints on the sum of neutrino masses, in combination with the latest laboratory measurements on oscillations, provide “decisive” Bayesian evidence for the normal neutrino mass hierarchy. We show that this result holds across very different prior alternatives by exploring two extremes on the range of prior choices. In fact, while the specific numerical value for the Evidence depends on the choice of prior, the Bayesian odds remain greater than 140:1 across very different prior choices. For Majorana neutrinos this has important implications for the upper limit of the neutrino-less double beta decay half life and thus for the technology and resources needed for future double beta decay experiments.

Characterization of inverted coaxial ^{76}Ge detectors in GERDA for future double-beta decay experiments

Neutrinoless double-beta decay of ^{76}Ge is searched for with germanium detectors where source and detector of the decay are identical. For the success of future experiments it is important to increase the mass of the detectors. We report here on the characterization and testing of five prototype detectors manufactured in inverted coaxial (IC) geometry from material enriched to 88% in ^{76}Ge. IC detectors combine the large mass of the traditional semi-coaxial Ge detectors with the superior resolution and pulse shape discrimination power of point contact detectors which exhibited so far much lower mass. Their performance has been found to be satisfactory both when operated in vacuum cryostat and bare in liquid argon within the Gerda setup. The measured resolutions at the Q-value for double-beta decay of ^{76}Ge (Q_{beta beta } = 2039 keV) are about 2.1 keV full width at half maximum in vacuum cryostat. After 18 months of operation within the ultra-low background environment of the GERmanium Detector Array (Gerda) experiment and an accumulated exposure of 8.5 kgcdot year, the background index after analysis cuts is measured to be 4.9^{+7.3}_{-3.4}times 10^{-4} text {counts}/(text {keV} cdot text {kg} cdot text {year}) around Q_{beta beta }. This work confirms the feasibility of IC detectors for the next-generation experiment Legend.

Possibilities of Future Double Beta Decay Experiments to Investigate Inverted and Normal Ordering Region of Neutrino Mass

An overview of modern experiments on the search for neutrinoless double decay is presented. The obtained limits on the effective mass of the Majorana neutrino $\langle m_{\nu} \rangle$ are discussed taking into account the uncertainties in the value of the nuclear matrix elements (NMEs) and the value of the axial-vector constant $g_A$. Predictions for the values of $\langle m_{\nu} \rangle$ from the results of oscillation experiments and modern cosmological data are presented. The possibilities of the next generation experiments with sensitivity to $\langle m_{\nu} \rangle$ at the level of $\sim$ 10-50 meV (studying mainly the inverted ordering (IO) region) are discussed. %Description of the most developed and promising projects is presented. The prospects for studying the normal ordering (NO) region are discussed too. It is shown that the possibilities of studying the NO depend on the mass of the lightest neutrino m$_0$. In the limiting case of small mass (m$_0$ $\le$ 0.1 meV), the values of $\langle m_{\nu} \rangle$ $\approx$ 1-4 meV are predicted, which makes the study of this region inaccessible by the next generation experiments. But there is an allowed region of m$_0$ (7-30 meV) in the framework of NO, where the predicted values for $\langle m_{\nu} \rangle$ could be $\sim$ 10-30 meV and that is quite achievable for the next generation experiments. The possibility to rich in the future sensitivity to $\langle m_{\nu} \rangle$ at the level of $\sim$ 1-10 meV is also discussed.

JUNO and neutrinoless double beta decay

We study the impact of the precision determination of oscillation parameters in the JUNO experiment on half-life predictions for neutrinoless double beta decay. We show that the solar neutrino mixing angle can be measured by JUNO with below 1% uncertainty. This implies in particular that the minimal value of the effective mass in the inverted mass ordering will be known essentially without uncertainty. We demonstrate that this reduces the range of half-life predictions in order to test this value by a factor of two. The remaining uncertainty is caused by nuclear matrix elements. This has important consequences for future double beta decay experiments that aim at ruling out the inverted mass ordering or the Majorana nature of neutrinos.

Neutrinoless double beta decay and lepton number violation at the LHC

We compare the discovery potential of the LHC for lepton number violating (LNV) signals with the sensitivity of current and future double beta decay experiments, assuming $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay is dominated by heavy particle exchange. We consider charged scalar, leptoquark and diquark mechanisms of $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay, covering the $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay operators with both, the smallest and largest, possible rates. We demonstrate, if $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay were found with a half-life below ${10}^{26}--{10}^{27}\text{ }\mathrm{\text{years}}$ a positive signal should show up at the LHC, except for some particular cases of the leptoquark mechanism, and vice versa, if the LHC does not find any hints for LNV, a ``short-range'' explanation for a finite $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decay half-life will be ruled out in most cases. We argue, if a positive LNV signal were found at the LHC, it is possible to identify the dominant contribution to $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$. Two different kinds of observables which could provide such ``model discriminating'' power are discussed: different invariant mass peaks and the charge asymmetry.

Real-time spectroscopy of solar pp-neutrinos using 150Nd

The potential real-time spectroscopy of solar pp-neutrinos using 150Nd as target is investigated. The threshold of 196 keV would be the lowest of all solar neutrino experiments running so far. Experimental rates and parameters are discussed, about 906 SNU can be expected from pp-neutrinos and another 574 SNU from 7Be. Furthermore, it is investigated whether charged current reactions might cause a new background component for future double beta decay experiments based on a large amount of 150Nd.

Double beta decay experiments

The present status of double beta decay experiments is reviewed. The results of the most sensitive experiments are discussed. Proposals for future double beta decay experiments with a sensitivity to the $< m_{\nu} >$ at the level of (0.01--0.1) eV are considered.

CdWO 4 scintillating bolometer for Double Beta Decay: Light and heat anticorrelation, light yield and quenching factors

We report the performances of a 0.51 kg CdWO 4 scintillating bolometer to be used for future Double Beta Decay Experiments. The simultaneous readout of the heat and the scintillation light allows to discriminate between different interacting particles aiming at the disentanglement and the reduction of background contribution, key issue for next generation experiments. We will describe the observed anticorrelation between the heat and the light signal and we will show how this feature can be used in order to increase the energy resolution of the bolometer over the entire energy spectrum, improving up to a factor 2.6 on the 2615 keV line of 208Tl. The detector was tested in a 433 h background measurement that permitted to estimate extremely low internal trace contaminations of 232Th and 238U. The light yield of γ/ β, α’s and neutrons is presented. Furthermore we developed a method in order to correctly evaluate the absolute thermal quenching factor of α-particles in scintillating bolometers.

Double-beta decay: Present status

The present status of double beta decay experiments (including the search for $2\beta^{+}$, EC$\beta^{+}$ and ECEC processes) are reviewed. The results of the most sensitive experiments are discussed. Average and recommended half-life values for two-neutrino double beta decay are presented. Conservative upper limits on effective Majorana neutrino mass and the coupling constant of the Majoron to the neutrino are established as $<m_{\nu} > < 0.75$ eV and $<g_{ee} > < 1.9 \cdot 10^{-4}$, respectively. Proposals for future double beta decay experiments with a sensitivity for the $<m_{\nu}>$ at the level of (0.01-0.1) eV are considered.

Neutrino mass patterns and future double-beta decay experiments

The next generation of double-beta decay experiments have an excellent chance of providing data on the neutrino mass pattern. This presentation is a summary of what is currently known about the mass pattern and expectations from experiment. Uncertainties due to the precision in the oscillation parameters are not critical to the interpretation of a ββ (0 ν ) measurement in terms of the mass pattern. Even though there is reason for optimism, the matrix element uncertainty is still a concern. A selected, representative group of the future experiments is discussed.