Measurement of the 2νββ Decay Rate and Spectral Shape of ^{100}Mo from the CUPID-Mo Experiment

Improved Limit on Neutrinoless Double Beta Decay of ^{100}Mo from AMoRE-I

AMoRE searches for the neutrinoless double beta decay using 100 kg of enriched ^{100}Mo. Scintillating molybdate crystals coupled with a metallic magnetic calorimeter operate at milli-Kelvin temperatures to measure the energy of electrons emitted in the decay. AMoRE-I is a demonstrator for the full-scale AMoRE, operated at the Yangyang Underground Laboratory for over two years. The exposure was 8.02  kg year (or 3.89  kg_{^{100}Mo} year), and the total background rate near the Q value was 0.025±0.002  counts/keV/kg/year. We observed no indication of 0νββ decay and report a new lower limit of the half-life of ^{100}Mo 0νββ decay as T_{1/2}^{0ν}>2.9×10^{24}  yr at 90% confidence level. The effective Majorana mass limit range is m_{ββ}<(210-610)  meV using nuclear matrix elements estimated in the framework of different models, including the recent shell model calculations.

First demonstration of a TES based cryogenic Li 2 MoO 4 detector for neutrinoless double beta decay search

Cryogenic calorimetric experiments to search for neutrinoless double-beta decay ( 0 ν β β ) are highly competitive, scalable and versatile in isotope. The largest planned detector array, CUPID, is comprised of about 1500 individual Li2 100 MoO4 detector modules with a further scale up envisioned for a follow up experiment (CUPID-1T). In this article, we present a novel detector concept targeting this second stage with a low impedance TES based readout for the Li2 MoO4 absorber that is easily mass-produced and lends itself to a multiplexed readout. We present the detector design and results from a first prototype detector operated at the NEXUS shallow underground facility at Fermilab. The detector is a 2-cm-side cube with 21 g mass that is strongly thermally coupled to its readout chip to allow rise-times of ∼ 0.5 ms. This design is more than one order of magnitude faster than present NTD based detectors and is hence expected to effectively mitigate backgrounds generated through the pile-up of two independent two neutrino decay events coinciding close in time. Together with a baseline resolution of 1.95 keV (FWHM) these performance parameters extrapolate to a background index from pile-up as low as 5 · 10 - 6  counts/keV/kg/yr in CUPID size crystals. The detector was calibrated up to the MeV region showing sufficient dynamic range for 0 ν β β searches. In combination with a SuperCDMS HVeV detector this setup also allowed us to perform a precision measurement of the scintillation time constants of Li2 MoO4 , which showed a primary component with a fast O(20  μ s) time scale.

Sensitivity Challenge of the Next-Generation Bolometric Double-Beta Decay Experiment

Cryogenic crystal bolometer plays a crucial role in searching for neutrinoless double-beta (0νββ) decay, which is a rare process that could determine the Majorana nature of neutrinos. The flagship bolometer experiment-CUORE (Cryogenic Underground Observatory for Rare Events)-operating at the Gran Sasso underground laboratory [Laboratori Nazionali del Gran Sasso (LNGS)] as the world's first ton-scale bolometric detector has achieved great success and well demonstrated advantages of the bolometric technology for the 0νββ study. The proposed upgrade of CUORE-the CUPID project-aims to achieve higher sensitivity with orders of magnitude background reduction by utilizing scintillating crystals and dual readout technology to exclude most of the background events dominated by alpha particles. Although CUPID has outstanding advantages over CUORE, further increasing the detection capability to fully explore the effective neutrino mass region for the inverted neutrino mass hierarchy and possibly to discover Majorana neutrinos remains a technical challenge ahead. In this prospective, we discuss strategies toward future technology development to further enhance the experimental sensitivity.

Simultaneous Measurement of the Half-Life and Spectral Shape of ^{115}In β Decay with an Indium Iodide Cryogenic Calorimeter

Current bounds on the neutrino Majorana mass are affected by significant uncertainties in the nuclear calculations for neutrinoless double-beta decay. A key issue for a data-driven improvement of the nuclear theory is the actual value of the axial coupling constant g_{A}, which can be investigated through forbidden β decays. We present the first measurement of the 4th-forbidden β decay of ^{115}In with a cryogenic calorimeter based on indium iodide. Exploiting the enhanced spectrum-shape method for the first time to this isotope, our study accurately determines simultaneously spectral shape, g_{A}, and half-life. The interacting shell model, which best fits our data, indicates a half-life for this decay at T_{1/2}=(5.26±0.06)×10^{14}  yr.

Measurement of the 2νββ Decay Half-Life of ^{82}Se with the Global CUPID-0 Background Model

We report on the results obtained with the global CUPID-0 background model, which combines the data collected in the two measurement campaigns for a total exposure of 8.82  kg×yr of ^{82}Se. We identify with improved precision the background sources within the 3 MeV energy region, where neutrinoless double β decay of ^{82}Se and ^{100}Mo is expected, making more solid the foundations for the background budget of the next-generation CUPID experiment. Relying on the excellent data reconstruction, we measure the two-neutrino double β-decay half-life of ^{82}Se with unprecedented accuracy: T_{1/2}^{2ν}=[8.69±0.05(stat)_{-0.06}^{+0.09}(syst)]×10^{19}  yr.