C. Pobes

Present status of MI-BETA cryogenic experiment and preliminary results for CUORICINO

Present results on neutrinoless double beta decay of 130Te obtained with an array of 20 cryogenic detectors are presented. The setup consists of 20 crystals of tellurium oxide of 340 g each, corresponding to the largest presently operating cryogenic mass. Combining the results of the few runs obtained with the same array, corresponding to 1.5 kg yr, a limit on neutrinoless double beta decay half-life of 9.5]1022 yr (90% CL) has been obtained. On the basis of the results obtained with the MI-BETA experiment, we propose a construction of a 42 kg array of 56 TeO 2 bolometers (CUORICINO project) to extend the sensitivity of the present experiment, and as a rst test for CUORE. Thanks to an innovative technique of vibration reduction and despite the high mass (750 g instead of the 340 g of the presently running detectors) we reached an energy resolution of 3.9 keV FWHM at 2615 keV decreasing to 1.4 keV at low energies. ( 2000 Elsevier Science B.V. All rights reserved.

A cryogenic underground observatory for rare events: Cuore, an update

CUORE is a proposed tightly packed array of 1000 TeO2 bolometers, each being a cube 5 cm on a side with a mass of 750 g. The array consists of 25 vertical towers, arranged in a square of 5 towers by 5 towers, each containing ten layers of four crystals. The design of the detector is optimized for ultralow-background searches for neutrinoless double beta decay of 130Te (33.8% abundance), cold dark matter, solar axions, and rare nuclear decays. A preliminary experiment involving 20 crystals of various sizes (MIBETA) has been completed, and a single CUORE tower is being constructed as a smaller scale experiment called CUORICINO. The expected performance and sensitivity, based on Monte Carlo simulations and extrapolations of present results, are reported.

High-resolution bolometers for rare events detection

Abstract Since many years the Milano–Gran Sasso collaboration is developing large mass calorimeters for Double Beta Decay and Dark Matter searches, employing TeO2 crystals as absorber elements. Recently, we have focused our attention on the improvement of the detector resolution: an efficient dumping suspension and the implementation of a new cold electronics device, have strongly suppressed the main sources of noise. The increase in S/N ratio has been of almost an order of magnitude and the resolution achieved is competitive with that of Ge diodes for γ-rays detection, while a FWHM of 3.2±0.3xa0keV has been obtained for 5.4xa0MeV alpha particles, the best result with any kind of detector.

Present and Future Cryogenic Experiments on Double-Beta Decay

Thermal detectors are introduced and their possible impact on neutrinoless double-beta-decay (2β0ν) search is discussed. The thermal experiment MIBETA is described, reporting the up-to-date limits on 130Te and 128Te. A new generation experiment, consisting in a large expansion of MIBETA and known as CUORE, is presented and discussed.

Dark Matter Results in the MIBETA Experiment

During a Double Beta Decay experiment performed at Laboratori Nazionali del Gran Sasso, a 274 hours low-threshold background spectra was collected with a 340 g TeO2 detector. The MIBETA experiment consists of 20 Tellurium oxide crystals working as bolometers at T = 10 mK in a dilution refrigerator. We present here the analysis carried out on a single detector to search for possible WIMP signal. The values of parameters which are essential in the search for WIMP’s, like energy resolution (∼ 2keV), energy threshold (10keV) and nuclear quenching factor (≃ 1) have been experimentally determined and are discussed in detail. The exclusion plot of the spin-independent cross section of WIMP’s on the nuclei is reported.

Dark matter search in the Milano double beta experiment and prospects for the CUORE project

A Double Beta Decay experiment performed by the Milano group at the Laboratori Nazionali del Gran Sasso (Mi DBD experiment) consists of 20 TeO2 crystals operated as bolometers at T ⋍ 10mK. An 89-day low-threshold background spectrum, collected with two 340 g bolometers, was selected and analyzed to search for a possible WIMP signal. The exclusion plot in a WIMP mass — cross section plane was evaluated, assuming WIMP-nucleus spin-independent interaction. WIMP-nucleon cross sections larger than 10−4 pb are excluded between 30 and 100 GeV WIMP masses. The planned expansions of the present experiment, named CUORICINO and CUORE, are presented in terms of sensitivity to WIMP search, considering also the seasonal modulation approach, made possible by the large masses of the future arrays (40 kg for CUORICINO and 760 kg for CUORE).

The CUORICINO and CUORE experiments

CUORE is an experiment intended to investigate rare events like the double beta decay and the interaction of cold dark matter and solar axions. It consists of a tightly packed array of 1000 TeO2 bolometers, having a mass of 750 g each, operating in the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. A first step towards CUORE is CUORICINO, an experiment with 40.7 kg of TeO2 running since the beginning of 2003 in Gran Sasso. In this paper, the CUORE project is described, the first results of CUORICINO for the neutrinoless double beta decay of Te are given, and the physics potential and prospects of both CUORICINO and CUORE are presented. Dedicated to Angel Morales

The CUORE experiment

The CUORE (Cryogenic Underground Observatory for Rare Events) experiment will be composed by one thousand TeO2 absorbers of 5×5×5u2009cm3 to be operated in the Gran Sasso Underground Laboratory. CUORICINO, a reduced version of CUORE, as been already approved and funded and will be in operation since the beginning of next year. A description of the CUORE setup, of the mechanical structure and of the single detector performances is shown. The physics goals of CUORE are illustrated.

Low-temperature high-Z gamma-detectors with very high energy resolution

High-Z low-temperature calorimeters are developed by an Italian collaboration (Milano-Como-Gran Sasso Underground Laboratories) in order to search for rare nuclear events and Dark Matter massive candidates. They exhibit an excellent energy resolution, close to that of Ge-diodes, but a much higher efficiency. Different high-Z materials were initially employed . A many-years optimisation work on tellurium oxide (TeO2) lead to impressive results: devices with total masses around 750 g present FWHM energy resolutions on gamma-ray peaks ranging from 1 KeV (close to the 5 KeV energy threshold) to 2.6 KeV at 2615 KeV (208Tl gamma line). A 3.2 KeV FWHM energy resolution was obtained at 5.4 MeV (210Po alpha line), which is by far the best one ever achieved with any alpha detector. These devices, operated at about 10 mK, consist of a TeO2 single crystal thermally coupled to a 50 mg Neutron Transmutation Doped (NTD) Ge crystal working as a temperature sensor. Special care was devoted to methods for response linearization and temporal stabilisation. Devices based on the same principle and specifically optimised could find applications in several fields like gamma-ray astrophysics, nuclear physics searches, environmental monitoring and radiation metrology.