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We present a search for beta plus/EC double beta decay of 120Te performed with the CUORICINO experiment, an array of TeO2 cryogenic bolometers. After collecting 0.0573 kg y of 120Te, we see no evidence of a signal and therefore set the following limits on the half-life: T1/2 (0nu) > 1.9 10^{21} y at 90% C.L. for the 0 neutrino mode and T1/2 (2nu) > 7.6 10^{19} y at 90% C.L. for the two neutrino mode. These results improve the existing limits by almost three orders of magnitude (four in the case of 0 neutrino mode).
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We report the results of a search for neutrinoless double-beta decay in a 9.8~kg$cdot$yr exposure of $^{130}$Te using a bolometric detector array, CUORE-0. The characteristic detector energy resolution and background level in the region of interest are $5.1pm 0.3{rm~keV}$ FWHM and $0.058 pm 0.004,(mathrm{stat.})pm 0.002,(mathrm{syst.})$~counts/(keV$cdot$kg$cdot$yr), respectively. The median 90%~C.L. lower-limit sensitivity of the experiment is $2.9times 10^{24}~{rm yr}$ and surpasses the sensitivity of previous searches. We find no evidence for neutrinoless double-beta decay of $^{130}$Te and place a Bayesian lower bound on the decay half-life, $T^{0 u}_{1/2}>$~$ 2.7times 10^{24}~{rm yr}$ at 90%~C.L. Combining CUORE-0 data with the 19.75~kg$cdot$yr exposure of $^{130}$Te from the Cuoricino experiment we obtain $T^{0 u}_{1/2} > 4.0times 10^{24}~mathrm{yr}$ at 90%~C.L.~(Bayesian), the most stringent limit to date on this half-life. Using a range of nuclear matrix element estimates we interpret this as a limit on the effective Majorana neutrino mass, $m_{betabeta}< 270$ -- $760~mathrm{meV}$.
The GERmanium Detector Array (GERDA) experiment searched for the lepton-number-violating neutrinoless double-$beta$ ($0 ubetabeta$) decay of $^{76}$Ge, whose discovery would have far-reaching implications in cosmology and particle physics. By operating bare germanium diodes, enriched in $^{76}$Ge, in an active liquid argon shield, GERDA achieved an unprecedently low background index of $5.2times10^{-4}$ counts/(keV$cdot$kg$cdot$yr) in the signal region and met the design goal to collect an exposure of 100 kg$cdot$yr in a background-free regime. When combined with the result of Phase I, no signal is observed after 127.2 kg$cdot$yr of total exposure. A limit on the half-life of $0 ubetabeta$ decay in $^{76}$Ge is set at $T_{1/2}>1.8times10^{26}$ yr at 90% C.L., which coincides with the sensitivity assuming no signal.
In the field of Double Beta Decay (DBD) searches the possibility to have high resolution detectors in which background can be discriminated is very appealing. This very interesting possibility can be largely fulfilled in the case of a scintillating bolometer containing a Double Beta Decay emitter whose transition energy exceeds the one of the natural gamma line of 208Tl. We present the latest results obtained in the development of such a kind of scintillating bolometer. For the first time an array of five CdWO4 (116Cd has a Double Beta Decay transition energy of 2805 keV) crystals is tested. The array consists of a plane of four 3x3x3 cm3 crystals and a second plane consisting of a single 3x3x6 cm3 crystal. This setup is mounted in hall C of the National Laboratory of Gran Sasso inside a lead shielding in order to reduce as far as possible the environmental background. The aim of this test is to demonstrate the technical feasibility of this technique through an array of detectors and perform a long background measurement in the best conditions in order to prove the achievable background in the Zero neutrino-DBD region.
A search for double $beta$ decay of dysprosium was realized for the first time with the help of an ultra low-background HP Ge $gamma$ detector. After 2512 h of data taking with a 322 g sample of dysprosium oxide limits on double beta processes in $^{156}$Dy and $^{158}$Dy have been established on the level of $T_{1/2}geq 10^{14}-10^{16}$ yr. Possible resonant double electron captures in $^{156}$Dy and $^{158}$Dy were restricted on a similar level. As a by-product of the experiment we have measured the radioactive contamination of the Dy$_2$O$_3$ sample and set limits on the $alpha$ decay of dysprosium isotopes to the excited levels of daughter nuclei as $T_{1/2}geq 10^{15} - 10^{17}$ yr.
The Standard Model of particle physics cannot explain the dominance of matter over anti-matter in our Universe. In many model extensions this is a very natural consequence of neutrinos being their own anti-particles (Majorana particles) which implies that a lepton number violating radioactive decay named neutrinoless double beta ($0 ubetabeta$) decay should exist. The detection of this extremely rare hypothetical process requires utmost suppression of any kind of backgrounds. The GERDA collaboration searches for $0 ubetabeta$ decay of $^{76}$Ge ($^{76}rm{Ge} rightarrow,^{76}rm{Se} + 2e^-$) by operating bare detectors made from germanium with enriched $^{76}$Ge fraction in liquid argon. Here, we report on first data of GERDA Phase II. A background level of $approx10^{-3}$ cts/(keV$cdot$kg$cdot$yr) has been achieved which is the world-best if weighted by the narrow energy-signal region of germanium detectors. Combining Phase I and II data we find no signal and deduce a new lower limit for the half-life of $5.3cdot10^{25}$ yr at 90 % C.L. Our sensitivity of $4.0cdot10^{25}$ yr is competitive with the one of experiments with significantly larger isotope mass. GERDA is the first $0 ubetabeta$ experiment that will be background-free up to its design exposure. This progress relies on a novel active veto system, the superior germanium detector energy resolution and the improved background recognition of our new detectors. The unique discovery potential of an essentially background-free search for $0 ubetabeta$ decay motivates a larger germanium experiment with higher sensitivity.
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