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Register a new userFirst Results from CUORE: A Search for Lepton Number Violation via $0 ubetabeta$ Decay of $^{130}$Te
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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: $^{130}$Te neutrinoless double-beta decay. Examining a total TeO$_2$ exposure of 86.3 kg$cdot$yr, characterized by an effective energy resolution of (7.7 $pm$ 0.5) keV FWHM and a background in the region of interest of (0.014 $pm$ 0.002) counts/(keV$cdot$kg$cdot$yr), we find no evidence for neutrinoless double-beta decay. The median statistical sensitivity of this search is $7.0times10^{24}$ yr. Including systematic uncertainties, we place a lower limit on the decay half-life of $T^{0 u}_{1/2}$($^{130}$Te) > $1.3times 10^{25}$ yr (90% C.L.). Combining this result with those of two earlier experiments, Cuoricino and CUORE-0, we find $T^{0 u}_{1/2}$($^{130}$Te) > $1.5times 10^{25}$ 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 $m_{betabeta}<(110 - 520)$ meV, where the range reflects the nuclear matrix element estimates employed.
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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, $m_{betabeta}< 270$ -- $760~mathrm{meV}$.
A detailed description of the CUORICINO $^{130}Te$ neutrinoless double-beta ($ bb$) decay experiment is given and recent results are reported. CUORICINO is an array of 62 tellurium oxide ($TeO_{2}$) bolometers with an active mass of 40.7 kg. It is cooled to $sim 8-10$ 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 $11.83textrm{kg}...textrm{y}$ or 91 mole-years of $^{130}Te$. No evidence for $ bb$-decay was observed and a limit of $T^{0 u}_{1/2}(^{130}Te)geq3.0times10^{24}$ y (90% C.L.) is set. This corresponds to an upper limit on the effective mass, $< m_{ u}>$, 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 $ bb$-decay by H.V. Klapdor-Kleingrothaus, textit{et al.} The experiment continues to acquire data.
We describe in detail the methods used to obtain the lower bound on the lifetime of neutrinoless double-beta ($0 ubetabeta$) decay in $^{130}$Te and the associated limit on the effective Majorana mass of the neutrino using the CUORE-0 detector. CUORE-0 is a bolometric detector array located at the Laboratori Nazionali del Gran Sasso that was designed to validate the background reduction techniques developed for CUORE, a next-generation experiment scheduled to come online in 2016. CUORE-0 is also a competitive $0 ubetabeta$ decay search in its own right and functions as a platform to further develop the analysis tools and procedures to be used in CUORE. These include data collection, event selection and processing, as well as an evaluation of signal efficiency. In particular, we describe the amplitude evaluation, thermal gain stabilization, energy calibration methods, and the analysis event selection used to create our final $0 ubetabeta$ decay search spectrum. We define our high level analysis procedures, with emphasis on the new insights gained and challenges encountered. We outline in detail our fitting methods near the hypothesized $0 ubetabeta$ decay peak and catalog the main sources of systematic uncertainty. Finally, we derive the $0 ubetabeta$ decay half-life limits previously reported for CUORE-0, $T^{0 u}_{1/2}>2.7times10^{24}$ yr, and in combination with the Cuoricino limit, $T^{0 u}_{1/2}>4.0times10^{24}$ yr.
We report on a search for double beta decay of $^{130}$Te to the first $0^{+}$ excited state of $^{130}$Xe using a 9.8 kg$cdot$yr exposure of $^{130}$Te collected with the CUORE-0 experiment. In this work we exploit different topologies of coincident events to search for both the neutrinoless and two-neutrino double-decay modes. We find no evidence for either mode and place lower bounds on the half-lives: $tau^{0 u}_{0^+}>7.9cdot 10^{23}$ yr and $tau^{2 u}_{0^+}>2.4cdot 10^{23}$ yr. Combining our results with those obtained by the CUORICINO experiment, we achieve the most stringent constraints available for these processes: $tau^{0 u}_{0^+}>1.4cdot 10^{24}$ yr and $tau^{2 u}_{0^+}>2.5cdot 10^{23}$ yr.
We measured two-neutrino double beta decay of $^{130}$Te using an exposure of 300.7 kg$cdot$yr accumulated with the CUORE detector. Using a Bayesian analysis to fit simulated spectra to experimental data, it was possible to disentangle all the major background sources and precisely measure the two-neutrino contribution. The half-life is in agreement with past measurements with a strongly reduced uncertainty: $T^{2 u}_{1/2} = 7.71^{+0.08}_{-0.06}mathrm{(stat.)}^{+0.12}_{-0.15}mathrm{(syst.)}times10^{20}$ yr. This measurement is the most precise determination of the $^{130}$Te 2$ ubetabeta$ decay half-life to date.
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