Session T13: Double Beta Decay II

Live

CUORE is one of the leading searches for neutrinoless double beta decay, a process which if discovered would show that lepton number conservation is violated and neutrinos are Majorana particles. CUORE uses an array of 988 individual TeO$_2$ crystals operated at approximately 11 mK as both the source material and as bolometric detectors to look for this process in $^{130}$Te. It is necessary that we understand the energy response of each bolometer thoroughly to maximize the sensitivity of the experiment. In this talk we describe the challenges of calibrating a large array of cryogenic detectors while minimizing the background. We also discuss the calibration procedures and the results used to establish the detector performance parameters for the neutrinoless double beta decay search.   

Live

The NEXT experiment is searching for Majorana neutrinos through the signature of neutrinoless double beta decay ($0 \nu \beta \beta$). Detection of this process would indicate that, unlike all other fundamental fermions, the neutrino is its own antiparticle, has a Majorana mass term, and lepton number is not conserved. In order to search for this process, NEXT utilizes an electroluminescent high pressure gaseous $^{136}$Xe time projection chamber (HPGXeTPC). This technology gives NEXT several key advantages, including excellent energy resolution ($\textless$ 1\% FWHM at the decay energy), and background rejection through track topology. The 100 kg NEXT-100 detector is under construction with installation and commissioning planned for late 2021. NEXT-100 is expected to reach a sensitivity of $2.8 \times 10^{25}$ years (90\% CL) for an exposure of 100 kg-year, or $6.0 \times 10^{25}$ years after an effective three years run time. We will discuss both the basic design and physics of the NEXT-100 detector.   

Live

CUPID-Mo is a demonstrator experiment for CUPID (CUORE Upgrade with Particle ID), the planned next-generation upgrade of the first ton scale cryogenic bolometric $0\nu\beta\beta$ decay experiment, CUORE (Cryogenic Underground Observatory for Rare Events). CUPID-Mo was operated at Laboratoire Souterrain de Modane in France as an array of 20 enriched Li$_{2}$$^{100}$MoO$_{4}$ (LMO) cylindrical crystals ($\sim$200g each) each featuring a Ge light detector (LD) all at $\sim$20 mK. The LMOs and LDs were instrumented with NTD sensors allowing for the collection of both heat and scintillation light. This dual mode of energy collection allows for $\alpha$ events to be distinguished from $\beta$/$\gamma$ events, significantly reducing the background from degraded $\alpha$s in the heat channel. CUPID-Mo has a demonstrated bolometric energy resolution of $\sim$7 keV (FWHM) at 2615 keV, complete $\alpha$ / $\beta$/$\gamma$ discrimination and very low radioactive contamination. Here we report an overview of the current leading results in the search for $0\nu\beta\beta$ with CUPID-Mo using $\sim$2 kg-years of exposure, an analysis using a $^{56}$Co source to characterize the energy resolution scaling, and an overview of other ongoing CUPID-Mo analyses.   

Live

The MAJORANA DEMONSTRATOR experiment is an array of p-type, point-contact (PPC) Ge detectors searching for neutrinoless double-beta decay in Ge-76 operating in a low background shield at the Sanford Underground Research Facilit. MAJORANA has reported an unprecedented energy resolution of 2.5 keV FWHM and one of the lowest backgrounds at the double-beta decay Q value of 2039 keV. The DEMONSTRATORS's results to date derive from 30 kg of PPC detectors enriched in Ge-76. After a recent hardware upgrade and swap of detectors, the array includes four (6.7 kg) of the larger inverted-coaxial point-contact (ICPC) detectors planned for the next-generation LEGEND experiment. The excellent energy resolution achieved relies, in part, on correcting for the trapping of charge carriers from an ionization event that would otherwise degrade the measured energy. Charge trapping along the drift path is a greater concern in the larger ICPC detectors. Improved algorithms based on pulse shape characteristics are developed to apply a charge trapping correction to the ICPC detectors and preserve their energy resolution potential. In this talk, we report on the improved charge trapping corrections and the energy performance of the ICPC detectors operating in the MAJORANA DEMONSTRATOR.   

Live

CUPID-Mo, located at the Laboratoire Souterrain de Modane, in France was a demonstrator for CUPID, a next generation search for $0 \nu \beta \beta$ in $^{100}$Mo. CUPID-Mo consisted of $20$ $\sim 200$ g Li$_2^{100}$MoO$_4$ scintillating bolometers with 20 Ge light detectors. It has demonstrated excellent crystal radiopurity ($^{238}$U $ ^{232}$Th chains $0.3 - 1$ $\mu Bq/kg$ for relevant isotopes), $\alpha$, $\beta/\gamma$ particle discrimination ($>99.9\%$), and energy resolution ($\sim 7$ keV FWHM at $2615$ keV). CUPID-Mo has placed the leading limit on the half life of $0 \nu \beta \beta$ in $^{100}$Mo of $T_{1/2}^{0 \nu}>1.5 \cdot 10^{24}$ yr with 90\% C.I. In this talk we present the status of analysis of double beta decays of $^{100}$Mo to excited states of $^{100}$Ru. In these decays, the electrons are accompanied by one or more de-excitation gamma lines. Multi-site events provide a very clear experimental spectrum technique to reduce background rates when searching for these gammas.   

Live

nEXO is a 5 tonne monolithic liquid xenon (LXe) time projection chamber (TPC) planned to search for the neutrinoless double beta decay of $^{136}$Xe with an estimated half-life sensitivity of $\sim 10^{28}$ years at 90$\%$ C.L., which was published in 2018. This talk will cover advancements made in terms of detector design, signal modelling and data analysis to support a refined estimate of the sensitivity and discovery potential of the nEXO experiment. In particular, we updated the detector geometry in line with most recent advancements in our engineering design, we implemented a more realistic and data-driven modelling of the light and charge channel signals and developed a Deep Neutral Network based analysis to discriminate between signal and background.   

Live

The nEXO experiment is a proposed next-generation search for the neutrinoless double beta decay (NDBD) of Xe-136. The primary detector will be a 5-ton, monolithic liquid xenon time projection chamber (TPC) with a target enriched to 90\% in the isotope of interest. To optimize the energy resolution and event reconstruction, calibrations are needed to map the spatial- and time-dependent detector response. While this is possible using conventional external radiation sources, the strong self-shielding of liquid xenon motivates the development of radiation sources which can be dissolved into the liquid xenon and injected into the detector. In this talk, I will describe recent simulations and experimental tests of two such sources, Rn220 and Xe127, which are being studied for use in nEXO.   

Live

SNO+ is a kilo-tonne scale low background neutrino detector with the ability to study a broad range of physics topics. The experiment completed taking data with water filling its innermost volume and the collaboration has published results on invisible nucleon decay search and $^{8}$B solar neutrino flux measurement. Currently, the internal water is being replaced by organic liquid scintillator, providing the scope for measurement of reactor, geo, and low-energy solar neutrinos. Finally, the scintillator will be loaded with tellurium-130 in order to search for neutrinoless double beta decay ($0\nu\beta\beta$), the main physics goal of SNO+. \\ This talk will give an overview of the SNO+ experiment, its current status and results to date. The preparation for $0\nu\beta\beta$ and the projected sensitivity will also be presented.   

Live

nEXO is a proposed next-generation experiment searching for the neutrinoless double beta decay of Xe-136. The tonne-scale detector will utilize ultra-low background liquid xenon technology, validated by the EXO-200 experiment. With 5000 kg of xenon enriched to 90{\%} in the isotope 136, nEXO has a projected half-life sensitivity of approximately 10\textasciicircum 28 years. Stringent radioactive background control and careful material selection are necessary to achieve such sensitivity. One of the potential background sources is radon daughter attachment to detector materials during their exposure to air. The decay of Po-210 can produce neutrons via ($\alpha $, n) reactions, followed by capture on Xe-136. The $\beta $-decay of Xe-137 would then create background events. A survey of the literature shows a wide range of measured radon daughter attachment lengths. To better understand the causes for this variability our group at the University of Alabama has started a measurement program using various materials relevant for nEXO, monitoring environmental parameters. In this talk I will present results of this study.