Figure 2. The energy spectrum in the region-of-interest with the best-fit curve (solid red) and the best fit-curve with the 0νββ decay component fixed to the 90% CI limit (dashed blue).

The search used the 988 TeO₂ crystal bolometers shown in Fig. 1. An observation of 0νββ decay would demonstrate lepton number violation and that the neutrino is a Majorana fermion (i.e., is its own antiparticle), as well as providing constraints to the absolute neutrino mass scale. This search, from the data collection period from April 2017 to July 2019 – about fourfold the exposure of CUORE’s first result, found no signal, as can be seen in the energy spectrum in Fig. 2. With no evidence for 0νββ decay, the collaboration set a new 90% CL lower limit on the ¹³⁰Te 0νββ decay half-life of 3.2 × 10²⁵ yr, corresponding to an effective Majorana mass of 75-350 meV. This new limit approaches the so-called inverted neutrino mass hierarchy band that will be probed by the next generation CUPID (CUORE Upgrade with Particle ID) detector. CUORE is a near ton-scale bolometric detector located underground in the Gran Sasso lab in Italy, and the collaboration consists of members from US, Italian, French, and Chinese institutions. The US DOE Office of Nuclear Physics supports the US component of CUORE, and Berkeley Lab is the lead DOE laboratory on CUORE. UC Berkeley physics professor and NSD senior faculty scientist Yury Kolomensky is the US Spokesperson of CUORE, and NSD staff scientist Brian Fujikawa leads the CUORE group at Berkeley Lab. UC Berkeley postdocs and NSD affiliates Giovanni Benato and Laura Marini led the data analysis team as well as the writing committee. NSD postdocs Ben Schmidt and Brad Welliver made significant contributions to this analysis.

Reference
D. Q. Adams et al., (CUORE Collaboration), Physical Review Letters 124, 122501 (2020).