CUORE
[1] An observation of neutrinoless double beta decay would conclusively show that neutrinos are Majorana fermions; that is, they are their own antiparticles.
[5] This is relevant to many topics in particle physics, including lepton number conservation, nuclear structure, and neutrino masses and properties.
In September 2014, as part of the testing of the CUORE dilution refrigerator, scientists in the CUORE collaboration cooled a copper vessel with a volume of one cubic meter to 6 mK (0.006 K, −273.144 °C) for 15 days, setting a record for the lowest temperature in the known natural universe over such a large contiguous volume.
[5][7][8][9] The CUORE detectors are TeO2 crystals used as low heat capacity bolometers, arranged into towers and cooled in a large cryostat to approximately 10 mK with a dilution refrigerator.
Temperature spikes from electrons emitted in Te double beta decays are collected for spectrum analysis.
The detectors are calibrated using 232Th, the first element in a long decay chain that includes several prominent gamma rays up to 2615 keV.
The crystals were grown by the Shanghai Institute of Ceramics at the Chinese Academy of Sciences with strict radiopurity requirements.
[10] The crystals are held in place by PTFE support in towers constructed from oxygen-free high thermal conductivity copper and were assembled under nitrogen inside gloveboxes in cleanrooms.
[15] CUORE is a scaled-up version of CUORE-0, hosted in a new custom-built cryostat capable of supporting a detector with a mass of approximately one ton.
[17] There is a 73-ton octagonal shield outside of the cryostat, constructed of lead and borated polyethlene, to reduce the number of environmental gamma rays and neutrons reaching the detector.
Final results using 19.75 kg·y of 130Te exposure set world-leading 90% limits on the 130Te 0νββ half-life of T 0ν½ > 2.8 × 1024 yr, with a background of 0.18 ± 0.01/(keV·kg·yr) near the 0νββ decay energy.
[20] The first paper detailing the initial performance of CUORE-0 was published in August 2014 using data taken March to September 2013, with 7.1 kg·yr exposure, showing backgrounds reduced by a factor of 6 compared to CUORICINO and an energy resolution of 5.7 keV.
[16] First results of the full CUORE experiment were published 2018 finding no evidence for neutrinoless double beta decay setting a 90% CI Bayesian lower limit for the lifetime of
