Session CB: Mini-Symposium on Searches for Double Beta Decay I

Looking for Nothing: Experimental Searches for Neutrinoless Double-Beta Decay

Substantial efforts are underway across the globe to test a claimed observation of neutrinoless double-beta decay and to probe the large parameter space corresponding to inverted-hierarchy neutrino masses. In this talk, I will discuss the importance of these efforts and give an overview of the experimental techniques being fielded. I will present an update on the current global status of the field, including searches ongoing and under construction. I will also discuss challenges and prospects for future searches with improved sensitivity capable of definitively testing the Majorana nature of the neutrino for the inverted hierarchy.   

Quest for Neutrinoless Double Beta Decay of $^{130}$Te with the CUORE Detector

The CUORE experiment, in the advanced stages of construction at Laboratori Nazionali del Gran Sasso (LNGS), aims to search for $0\nu\beta\beta$ decay of $^{130}$Te with unprecedented sensitivity: \mbox{$T_{1/2}^{0\nu}=9.5 \times 10^{25}$ yr} at $90\%$ C.L. The detector will consist of 19 towers, each comprising 13 planes of four, 125~cm$^{3}$, cubic TeO$_{2}$ crystals. This amounts to a total mass of 206~kg of $^{130}$Te. When cooled to an operating temperature of \mbox{$\sim 10$~mK} such crystals function as highly sensitive bolometers with energy resolution better than $5\,$keV demonstrated near the $0\nu\beta\beta$ decay Q-value (\mbox{2527.518 $\pm$ 0.013~keV}). In this talk I will describe the expected reach of CUORE considering the rigorous cleaning, materials handling, and ultra-pure assembly techniques developed by the collaboration. I will also report on the status of CUORE-0, a single CUORE-like tower where many of these background mitigation techniques were deployed during assembly. CUORE-0 represents a new $0\nu\beta\beta$ experiment which is already operating at LNGS and will surpass the sensitivity of the previous generation experiment (Cuoricino) before CUORE begins operating.   

Neutrinoless double beta decay with SNO+

The SNO+ experiment is the successor to the Sudbury Neutrino Observatory (SNO), in which SNO's heavy water is replaced by approximately 780$\,$T of liquid scintillator (LAB). The combination of the 2$\,$km underground location, the use of ultra-clean materials and the high light-yield of the liquid scintillator means that a low background level and a low energy threshold can be achieved. This creates a new multipurpose neutrino detector with the potential to address a diverse set of physics goals, including the detection of reactor, solar, geo- and supernova neutrinos. A main physics goal of SNO+ is the search for neutrinoless double beta decay. By loading the liquid scintillator with 0.3$\%$ of natural Tellurium, resulting in about 800$\,$kg of $^{130}$Te (isotopic abundance is slightly over 34 $\%$), a competitive sensitivity to the effective neutrino mass can be reached. This talk will present the status of the SNO+ detector, and then discuss the plans and goals of the double beta decay phase.   

The Majorana Demonstrator: Design and Prospects

The continuing search for neutrinoless double beta decay, a rare process that may inform the absolute mass scale of the neutrino, is challenged by a persistent continuum background at energies below 5 MeV. The goal of the Majorana Demonstrator is to show the feasibility of reducing these backgrounds below~1 count/tonne*year in the 4keV ROI around the Q-value at 2039 keV. The demonstrator will field an array of highly purified point contact germanium detectors to demonstrate the effectiveness of a suite of materials assay, construction and analysis techniques. We provide an overview of the experimental requirements, design and expected sensitivity.   

Resonant double-electron capture to excited nuclear states in $^{156}$Dy

Resonant double-electron capture is a possible experimental alternative to neutrinoless double-beta decay. If the Q-value of the decay is degenerate with an excited state in the daughter nucleus, a resonant enhancement effect can occur and decrease the half-life of the decay. As no phase space is available for neutrinos, this decay is only likely to proceed for Majorana neutrinos. Resonant ECEC may be detected by observing the $\gamma$ rays emitted as the excited state decays to the ground state. In this experiment, two Clover HPGe detectors surround a DyO$_2$ target and search for the deexcitation $\gamma$ rays. The apparatus is housed at the Kimballton Underground Research Facility (KURF) in Virginia. The experiment is hindered by the extremely low natural abundance of $^{156}$Dy: 0.052\%. We present new limits for the lifetime of this decay.   

Systematics of Evaluated Half-Lives of Double-Beta Decay

A new evaluation of 2$\beta$-decay half lives and their systematics is presented. These data extend the previous evaluation and include the analysis of all recent measurements. The nuclear matrix elements for 2$\beta$-decay transitions in 12 nuclei have been extracted. The recommended values are compared with the large-scale shell-model, QRPA calculations, and experimental data. A T$^{2\nu}_{1/2 }$ $\sim$ 1/E$^{8}$ systematic trend has been observed for recommended $^{128,130}$Te values. This trend indicates similarities for nuclear matrix elements in Te nuclei and was predicted for 2$\beta$(2$\nu$)-decay mode. The complete list of results is available online at http://www.nndc.bnl.gov/bbdecay/.   

Two-neutrino double-beta decay of $^{150}$Nd to excited final states

This study yields the first detection of the coincidence gamma rays from the 0$^+_1$ excited state of $^{150}$Sm. These gamma rays have energies of 333.97 keV and 406.52 keV, and are emitted in coincidence through a 0$^+_1\rightarrow$2$^+_1\rightarrow$0$^+_{gs}$ transition. The enriched Nd$_2$O$_3$ sample obtained from Oak Ridge National Laboratory consists of 40.13 g $^{150}$Nd. This sample was observed for 642.8 days at the Kimballton Underground Research Facility, producing 21.6 net events in the region of interest. This count rate gives a half life of $T_{1/2}=1.07^{+0.45}_{-0.25}(stat)\pm0.07(syst.))$ years, which agrees within uncertainties with another recent measurement in which no coincidence was employed. Lower limits were also obtained for decays to higher excited final states. Finally, the nuclear matrix element was extracted from this half life with a value of 0.0232$^{+0.0032}_{-0.0037}$.