M. Pedretti

130Te Neutrinoless Double-Beta Decay with CUORICINO

Abstract We report the final result of the CUORICINO experiment. Operated between 2003 and 2008, with a total exposure of 19.75xa0kgxa0·xa0y of 130 Te, CUORICINO was able to set a lower bound on the 130 Te 0 νββ half-life of 2.8xa0×xa010 24 xa0years at 90% C.L. The limit here reported includes the effects of systematic uncertainties that are examined in detail in the paper. The corresponding upper bound on the neutrino Majorana mass is in the range 300–710xa0meV, depending on the adopted nuclear matrix element evaluation.

A calorimetric search on double beta decay of 130Te

We report on the final results of a series of experiments on double beta decay of 130 Te carried out with an array of twenty cryogenic detectors. The set-up is made with crystals of TeO2 with a total mass of 6.8 kg, the largest operating one for a cryogenic experiment. Four crystals are made with isotopically enriched materials: two in 128 Te and two others in 130 Te. The remaining ones are made with natural tellurium, which contains 31.7% and 33.8% 128 Te and 130 Te, respectively. The array was run under a heavy shield in the Gran Sasso Underground Laboratory at a depth of about 3500 m.w.e. By recording the pulses of each detector in anticoincidence with the others a lower limit of 2.1 × 10 23 years has been obtained at the 90% C.L. on the lifetime for neutrinoless double beta decay of 130 Te. In terms of effective neutrino mass this leads to the most restrictive limit in direct experiments, after those obtained with Ge diodes. Limits on other lepton violating decays of 130 Te and on the neutrinoless double beta decay of 128 Te to the ground state of 128 Xe are also reported and discussed. An indication is presented for the two neutrino double beta decay of 130 Te. Some consequences of the present results in the interpretation of geochemical experiments are discussed. uf6d9 2003 Elsevier Science B.V. All rights reserved.

Muon-induced backgrounds in the CUORICINO experiment

Abstract To better understand the contribution of cosmic ray muons to the CUORICINO background, 10 plastic scintillator detectors were installed at the CUORICINO site and operated during the final 3xa0months of the experiment. From these measurements, an upper limit of 0.0021xa0counts/(keVxa0kgxa0yr) (95% CL) was obtained on the cosmic ray-induced background in the neutrinoless double beta decay region of interest. The measurements were also compared to Geant4 simulations.

Comparison of Lithium Gadolinium Borate Crystal Grains in Scintillating and Nonscintillating Plastic Matrices

We present a method for detecting neutrons using scintillating lithium gadolinium borate crystal grains in a plastic matrix while maintaining high gamma rejection. We have procured two cylindrical detectors, 5 × 5, containing 1% crystal by mass and with the crystal grains having a typical dimension of 1 mm. One detector was made with scintillating plastic, and one with nonscintillating plastic. Pulse shape analysis was used to reject gamma ray backgrounds. The scintillating detector was measured to have an intrinsic fast fission neutron efficiency of 0.4% and a gamma sensitivity <; 4.93 × 10-9, while the nonscintillating detector had a neutron efficiency of 0.6 or 0.7%, depending on analysis integration limits, with gamma sensitivity <; 4.93 × 10-9 and (3.25 ±2.84) × 10-7, respectively. We determine that increasing the neutron detection efficiency by a factor of 5-6 will make the detector competitive with moderated 3He tubes, and we discuss several simple and straightforward methods for obtaining or surpassing such an improvement. We end with a discussion of possible applications, both for the scintillating-plastic and nonscintillating-plastic detectors.

Search for double-β decay of 130Te to the first 0+ excited state of 130Xe with the CUORICINO experiment bolometer array

E. Andreotti, 2, a C. Arnaboldi, F. T. Avignone III, M. Balata, I. Bandac, M. Barucci, 7 J. W. Beeman, F. Bellini, 10 C. Brofferio, 3 A. Bryant, 12 C. Bucci, L. Canonica, 14 S. Capelli, 3 L. Carbone, M. Carrettoni, 3 M. Clemenza, 3 O. Cremonesi, R. J. Creswick, S. Di Domizio, 14 M. J. Dolinski, 15 L. Ejzak, R. Faccini, 10 H. A. Farach, E. Ferri, 3 E. Fiorini, 3, b L. Foggetta, 2, c A. Giachero, L. Gironi, 3 A. Giuliani, 2, d P. Gorla, e E. Guardincerri, 11, 14 T. D. Gutierrez, E. E. Haller, 18 K. Kazkaz, L. Kogler, 12 S. Kraft, 3 C. Maiano, 3 C. Martinez, f M. Martinez, 19, g R. H. Maruyama, S. Newman, 5 S. Nisi, C. Nones, 2, h E. B. Norman, 20 A. Nucciotti, 3 F. Orio, 10 M. Pallavicini, 14 V. Palmieri, L. Pattavina, 3 M. Pavan, 3 M. Pedretti, G. Pessina, S. Pirro, E. Previtali, L. Risegari, 7 C. Rosenfeld, C. Rusconi, 2 C. Salvioni, 2 S. Sangiorgio, i D. Schaeffer, 3 N. D. Scielzo, M. Sisti, 3 A. R. Smith, C. Tomei, G. Ventura, 7 and M. Vignati 10 Dipartimento di Fisica e Matematica, Università dell’Insubria, Como I-22100 Italy INFN Sezione di Milano Bicocca, Milano I-20126 Italy Dipartimento di Fisica, Università di Milano-Bicocca, Milano I-20126 Italy Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208 USA INFN Laboratori Nazionali del Gran Sasso, Assergi (L’Aquila) I-67010 Italy Dipartimento di Fisica, Università di Firenze, Firenze I-50125 Italy INFN Sezione di Firenze, Firenze I-50125 Italy Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA Dipartimento di Fisica, Sapienza Università di Roma, Roma I-00185 Italy INFN Sezione di Roma, Roma I-00185 Italy Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA Department of Physics, University of California, Berkeley, CA 94720 USA Dipartimento di Fisica, Università di Genova, Genova I-16146 Italy INFN Sezione di Genova, Genova I-16146 Italy Lawrence Livermore National Laboratory, Livermore, CA 94550 USA Department of Physics, University of Wisconsin, Madison, WI 53706 USA Physics Department, California Polytechnic State University, San Luis Obispo, CA 93407 USA Department of Materials Science and Engineering, University of California, Berkeley, CA 94720 USA Laboratorio de Fisica Nuclear y Astroparticulas, Universidad de Zaragoza, Zaragoza 50009 Spain Department of Nuclear Engineering, University of California, Berkeley, CA 94720 USA INFN Laboratori Nazionali di Legnaro, Legnaro (Padova) I-35020 Italy EH&S Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA (Dated: February 1, 2013)

Composite macro-bolometers for the rejection of surface radioactive background in rare-event experiments

Abstract Experiments searching for rare events, such as neutrinoless double beta decay and interactions of dark matter candidates, require extremely low levels of background. When these experiments are performed using macro-bolometers, radioactive contamination near the surfaces is of particular concern. For a bolometric neutrinoless double beta decay experiment, it can cause counts in the spectral region where the signal is expected, while for a dark matter experiment which exploits ionization signals for particle identification, it originates an incomplete charge collection simulating a nuclear recoil. In order to control the effects of surface contamination, we developed a novel technique that uses composite macro-bolometers to identify energy depositions that occur close to the surfaces of materials immediately surrounding the detector. The composite macro-bolometer proposed and studied here consists of a main energy absorber that is thermally coupled to and entirely surrounded by thin absorbers that act as active shields. Surface energy depositions can be rejected by the analysis of simultaneous signals in the main absorber and the shields. In this paper, we describe a full thermal model and experimental results for three prototype detectors. The detectors consist of Ge, Si, or TeO2 thin absorbers as active shields, all with TeO2 crystals as main absorbers. In all cases, the surface event rejection capability is clearly demonstrated. In addition, simulations and preliminary results show that it is possible to detect energy depositions that occurred on the shields without separate readout channels for them. The energy depositions in the shields are distinguished from those in the main absorber through pulse shape discrimination. This simplification makes this technique a viable method for the rejection of surface energy depositions in next-generation bolometric double beta decay searches, such as possible extensions or upgrades of the CUORE experiment.

Search for β+/EC double beta decay of 120Te

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).

Search for beta plus/EC double beta decay of 120Te

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).

Large mass bolometers for neutrinoless double beta decay detection: model and last results

Milano collaboration has been developing for many years large mass bolometers for particle detection, and in particular for the study of neutrinoless double beta decay of 130Te. The active components of the detectors are large mass (340 g and 790 g) TeO2 crystals, while Neutron Transmutation Doped Ge thermistors are used as phonon sensors. These devices work at low temperatures, about 5-10 mK. The mechanical and thermal connections of the detector to the thermal bath are made with PTFE pieces that hold the crystal on copper frames. Gold wires are used as electric connections. We have developed a complete thermal model for the bolometers and ad hoc measurements of the thermal parameters involved were performed in the Florence cryogenic laboratory. These studies have permitted to simulate the static and dynamic behaviours of the detectors. A satisfactory agreement between simulated and the experimental response has been obtained as far as the static behaviour is concerned, while the dynamic behaviour is not yet fully understood. These preliminary results however will enable us to design new detector structures in order to improve the signal-to-noise ratio and the reproducibility. Given the good performances of these devices (excellent energy resolutions were obtained, of the order of 2 keV at 911 keV and of 5 keV at 2615 keV), this technique is particularly suitable to detectors for gamma ray spectroscopy. Encouraged by this results, the Milano-Como group has joined a large international collaboration for the realization of CUORE (Cryogenic Underground Observatory for Rare Events), seraching for Dark Matter and neutrinoless Double Beta Decay, a crucial phenomenon for neutrino physics. The Cuoricino detector, a small scale test of CUORE detector, is an array of 62 large mass bolometers like those already described, and it is now in operation in the Gran Sasso undergrand laboratory (Italy). It is the largest array of bolometric detectors ever constructed.