Session FG: Neutrinoless Double Beta Decay I

Searching for Neutrinoless Double Beta Decay in Ge-76 with LEGEND

Neutrinoless double beta decay (0$\nu \beta \beta )$ is a hypothetical lepton-number-violating process that is possible only if neutrinos are Majorana particles, $i.e$. fermions that are their own antiparticles. The discovery of 0$\nu \beta \beta $ would unambiguously establish the Majorana nature of neutrinos and explicitly show that the total lepton number is violated. In their search for 0$\nu \beta \beta $ in $^{\mathrm{76}}$Ge, the GERDA and \textsc{Majorana Demonstrator} (MJD) experiments have achieved the best energy resolution in all 0$\nu \beta \beta $ experiments as well as unprecedented low background in the signal region. The Large Enriched Germanium Experiment for Neutrionless double beta Decay (LEGEND) combines the best technologies of both GERDA and MJD. LEGEND aims to develop a phased, $^{\mathrm{76}}$Ge based 0$\nu \beta \beta $ experimental program with a discovery potential of a half-life beyond 10$^{\mathrm{28}}$ years. The initial phase of LEGEND, LEGEND-200, with 200 kg of active mass is under construction utilizing retrofitted GERDA infrastructure, and plans to start data-taking in 2021. The subsequent phase, LEGEND-1000, will deploy 1000 kg of active mass. In this talk, we will overview the LEGEND program, including the physics goals and the status of LEGEND-200 construction and LEGEND-1000 preparation.   

Study of (alpha,n) reactions from the Calibration Sources of the MAJORANA DEMONSTRATOR Experiment

Neutrinoless double beta $(0 \nu \beta \beta)$ decay is a hypothesized lepton-number-violating nuclear transition. If observed, $0 \nu \beta \beta $ decay would unambiguously demonstrate the violation of an empirical symmetry of the Standard Model and establish the Majorana nature of neutrinos. The MAJORANA DEMONSTRATOR experiment, currently operating at the 4850$^{\prime}$ level of the Sanford Underground Research Facility in Lead SD, is searching for such decay in $^{76}$Ge with high purity Germanium (HPGe) detectors. MAJORANA has achieved an excellent energy resolution of 2.5 keV FWHM and a low background rate. The DEMONSTRATOR regularly deploys a $^{228}$Th line source to perform energy calibration based on the detection of the gamma ray photopeaks. The calibration source inevitably produces several alpha particles with energies of several MeV within the $^{228}$Th chain before it ends with the stable $^{208}$Pb. When traversing through surrounding materials, these alpha particles can potentially produce neutrons and coincident gammas from $(\alpha, n)$ reactions and nuclear de-excitations that follow. In this talk, we will discuss our efforts studying such neutrons originating from the calibration sources via their coincident gamma signatures.   

Mock data production for pileup rejection studies in CUPID

CUPID (CUORE Upgrade with Particle IDentification) is the proposed upgrade to the tonne-scale cryogenic bolometric experiment CUORE. In order to better understand the possible performance of the CUPID detector a simulation of the data can help identify areas for optimization. In the simulation of detector performance the pulse characteristics and the electronic noise are important features to take into account. The inclusion of these features allows us to consider the effect of detector non-idealities on the analysis, enabling a full evaluation of the performance of the chosen algorithms. To accomplish this a software tool cabable of generating a simulated noise baseline with fake pulses has been developed. These mock data can be used to produce controlled sets of data useful for the validation or training of new analysis procedures. In this contribution, the developed algorithm will be presented, alongside its application to the study of pileup rejection in the CUPID experiment.   

Studying CUORE Pulses with Principal Component Analysis

CUORE is a tonne-scale cryogenic bolometric experiment searching for the neutrinoless double beta decay of $^{130}$Te, operating a total of 988 TeO$_2$ crystals at a temperature of ~10 mK. The pulse shapes of triggered events in CUORE contain additional information that can be used to reject undesirable events, such as pileups and spurious triggers mimicking the energy signature of real physics events. Principal component analysis (PCA) is a method of dimensionality reduction that allows one to find the components that explain the most variance in a set of data. In this talk we present results from applying PCA to CUORE pulses and discuss its potential for pulse shape discrimination.   

Projected Backgrounds and Mitigation Techniques for the CUPID Experiment

The CUORE Upgrade with Particle IDentification (CUPID), is the proposed next-generation experiment of Cryogenic Underground Laboratory for Rare Events (CUORE). CUPID is a ton-scale search for neutrinoless double-beta decay. An observation of this ultra-rare decay would determine that neutrinos are Majorana particles, leading to new physics beyond the standard model. CUPID plans to utilize the knowledge and cryogenics of the ton-scale CUORE experiment with a new array of Mo bolometers and light detectors. CUPID will reach increased discovery sensitivities by significantly reducing background in its region of interest through passive and active techniques. With CUPID’s upgrades, cosmogenic muons become the most significant background. An active muon veto system is under development to mitigate this background. The major background contributions projected for the CUPID experiment, and the use of a muon veto to remove the cosmogenic-induced backgrounds will be discussed in this talk.   

Analysis Techniques for Background Reduction and Event Identification in the Search for Neutrinoless Double Beta Decay with CUORE

CUORE, the Cryogenic Underground Observatory for Rare Events, is an ton-scale bolometeric experiment based at the Gran Sasso National Laboratory in Italy primarily searching for neutrinoless double beta decay~(0$\nu \beta \beta$) in $^{130}$Te. The detector is composed of 988 TeO$_{2}$ crystals (5 x 5 x 5 cm$^3$ each) arranged into an array of 19 towers. CUORE has high sensitivity to 0$\nu \beta \beta$ by leveraging its low background environment, excellent energy resolution, and high modularity in conjunction with advanced analysis tools. In this presentation, we describe the key analysis techniques used in CUORE's search for 0$\nu \beta \beta$.   

A Low Energy Rare Event Search with the Majorana Demonstrator

The \textsc{Majorana Demonstrator} is an array of ultra-low background, P-type point contact (PPC) high-purity germanium (HPGe) detectors, with excellent energy resolution, keV-scale thresholds, and low cosmogenic activation. In addition to the primary search for neutrinoless double beta decay, we are searching for new physics beyond the Standard Model in the low-energy region under 100 keV, including bosonic dark matter and solar axions. Significant progress has been made in developing new data filters to automatically extract physics events at low energy, across the multi-year operational period of the \textsc{Demonstrator}. In this talk, we present a review of our rare event searches, and an update on new results.   

Recent Results from NEXT-NEW

It is currently unknown if neutrinos are Majorana particles, a property that would transform our understanding of the nature and mass of neutrinos. The NEXT experiment is searching for Majorana neutrinos through neutrinoless double beta decay $(0\nu\beta\beta)$ in a high pressure gaseous xenon time projection chamber. The NEXT collaboration has shown through a phased approach that this technology can achieve excellent energy resolution and great tracking capabilities. Here we present the latest results of the current detector, NEXT-NEW, including the energy resolution measurements, the power of the topological reconstruction, and the latest measurement of the two-neutrino double beta decays.