The CUORE experiment, a ton-scale cryogenic bolometer array, recently began operation at the Laboratori Nazionali del Gran Sasso in Italy. The array represents a significant advancement in this technology, and in this work we apply it for the first time to a high-sensitivity search for a lepton-number-violating process: ${}^{130}\mathrm{Te}$ neutrinoless double-beta decay. Examining a total ${\mathrm{TeO}}_2$ exposure of 86.3 kg yr, characterized by an effective energy resolution of $(7.7\pm 0.5)\mathrm{keV}$ FWHM and a background in the region of interest of $(0.014\pm 0.002)\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$, we find no evidence for neutrinoless double-beta decay. Including systematic uncertainties, we place a lower limit on the decay half-life of $T_{1/2}^{0\nu }({}^{130}\mathrm{Te})>1.3\times {10}^{25}\mathrm{yr}$ (90% C.L.); the median statistical sensitivity of this search is $7.0\times {10}^{24}\mathrm{yr}$. Combining this result with those of two earlier experiments, Cuoricino and CUORE-0, we find $T_{1/2}^{0\nu }({}^{130}\mathrm{Te})>1.5\times {10}^{25}\mathrm{yr}$ (90% C.L.), which is the most stringent limit to date on this decay. Interpreting this result as a limit on the effective Majorana neutrino mass, we find $m_{\beta \beta }<(110-520)\mathrm{meV}$, where the range reflects the nuclear matrix element estimates employed.

We report the results of a search for neutrinoless double-beta decay in a 9.8 kg yr exposure of ${}^{130}\mathrm{Te}$ using a bolometric detector array, CUORE-0. The characteristic detector energy resolution and background level in the region of interest are $5.1\pm 0.3\mathrm{keV}$ FWHM and $0.058\pm 0.004(\text{stat})\pm 0.002(\text{syst})\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$, respectively. The median 90% C.L. lower-limit half-life sensitivity of the experiment is $2.9\times {10}^{24}\mathrm{yr}$ and surpasses the sensitivity of previous searches. We find no evidence for neutrinoless double-beta decay of ${}^{130}\mathrm{Te}$ and place a Bayesian lower bound on the decay half-life, $T_{1/2}^{0\nu }>2.7\times {10}^{24}\mathrm{yr}$ at 90% C.L. Combining CUORE-0 data with the 19.75 kg yr exposure of ${}^{130}\mathrm{Te}$ from the Cuoricino experiment we obtain $T_{1/2}^{0\nu }>4.0\times {10}^{24}\mathrm{yr}$ 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, $m_{\beta \beta }<270–760\mathrm{meV}$.

We report new results from the search for neutrinoless double-beta decay in ${}^{130}\hspace{0.17em}\mathrm{Te}$ with the CUORE detector. This search benefits from a fourfold increase in exposure, lower trigger thresholds, and analysis improvements relative to our previous results. We observe a background of $(1.38\pm 0.07)\times {10}^{-2}\mathrm{counts}/(\mathrm{keV}\mathrm{kg}\mathrm{yr})$) in the $0\nu \beta \beta$ decay region of interest and, with a total exposure of 372.5 kg yr, we attain a median exclusion sensitivity of $1.7\times {10}^{25}\mathrm{yr}$. We find no evidence for $0\nu \beta \beta$ decay and set a 90% credibility interval Bayesian lower limit of $3.2\times {10}^{25}\mathrm{yr}$ on the ${}^{130}\hspace{0.17em}\mathrm{Te}$ half-life for this process. In the hypothesis that $0\nu \beta \beta$ decay is mediated by light Majorana neutrinos, this results in an upper limit on the effective Majorana mass of 75–350 meV, depending on the nuclear matrix elements used.

A detailed description of the CUORICINO ${}^{130}\mathrm{Te}$ neutrinoless double-beta $(0\hspace{0.5em}\nu \beta \beta )$ decay experiment is given and recent results are reported. CUORICINO is an array of 62 tellurium oxide (${\mathrm{TeO}}_2$) bolometers with an active mass of 40.7 kg. It is cooled to $~8\text{−}10$ mK by a dilution refrigerator shielded from environmental radioactivity and energetic neutrons. It is running in the Laboratori Nazionali del Gran Sasso (LNGS) in Assergi, Italy. These data represent an exposure of 11.83 kg yr or 91 mole-years of ${}^{130}\mathrm{Te}$. No evidence for $0\hspace{0.5em}\nu \beta \beta$-decay was observed and a limit of $T_{1/2}^{0\hspace{0.5em}\nu }({}^{130}\mathrm{Te})⩾3.0\times {10}^{24}\hspace{0.5em}\mathrm{y}$ (90% CL) is set. This corresponds to an upper limit on the effective mass, $\langle m_{\nu }\rangle$, between 0.19 and $0.68$ eV when analyzed with the many published nuclear structure calculations. In the context of these nuclear models, the values fall within the range corresponding to the claim of evidence of $0\hspace{0.5em}\nu \beta \beta$-decay by H. V. Klapdor-Kleingrothaus et al. The experiment continues to acquire data.

Neutrinoless double-beta (0νββ) decay is a hypothesized lepton-number-violating process that offers the only known means of asserting the possible Majorana nature of neutrino mass. The Cryogenic Underground Observatory for Rare Events (CUORE) is an upcoming experiment designed to search for 0νββdecay of¹³⁰Te using an array of 988 TeO₂crystal bolometers operated at 10 mK. The detector will contain 206 kg of¹³⁰Te and have an average energy resolution of 5 keV; the projected 0νββdecay half-life sensitivity after five years of livetime is 1.6 × 10²⁶ y at 1σ(9.5 × 10²⁵ y at the 90% confidence level), which corresponds to an upper limit on the effective Majorana mass in the range 40–100 meV (50–130 meV). In this paper, we review the experimental techniques used in CUORE as well as its current status and anticipated physics reach.