Last Update: October 2000

CUORE (Berkeley, Florence, LNGS, Leiden, Milan, U.C. South Carolina, Zaragoza collaboration)

Laboratory and beam: LNGS for cryogenic measurements, Milano-Bicocca for Radioactivity Measurements and Lawrence Berkeley Laboratory for the thermistor production and optimization

1. Goal of the experiment

CUORE is the acronym for "Cryogenic Underground Observatory for Rare Events". It consists in a series of experiments with very massive cryogenic detectors to investigate rare processes like double beta decay, interactions of Weakly Interacting Massive Particles (WIMPS) and solar axions and to search for rare nuclear decays. In all these searches macrobolometers, which reach now masses of almost a kilogram, present the advantage of a very good resolution and of uncommon versatility allowing an ample choice of nuclei in different compounds. This is particularly promising in experiments on double beta decay or on interactions of WIMPS where various good thermal absorbers containing the candidate nucleus are available.

We are presently operating in Hall A an array of twenty crystals of TeO2 with a total mass of 6.8 kg, by far the largest in the world for a cryogenic detector. A second experiment named CUORICINO, made with an array of 56 larger detectors with a total mass of 42 kilograms has been approved and funded and R&D for this array are actively pursued in Hall C. A third experiment, named CUORE, with an array of 1020 crystals with a total mass of 780 kilogram is being designed.

2. Physics achievements during 2000

In this year the group has obtained with the 20 crystal array in 4000 hours of effective running time and published new results on double beta decay of 130Te. Limits of 1.44 x 1023 , 1 x 1021 and 3 x 1020 years for the neutrinoless, majoron and two neutrino channels have been reached, respectively. We would like to note that the first two of these results are the most restrictive in literature after those obtained on 76Ge with semiconductor detectors. A better command of the electronics noise has recently considerably reduced the background in the low energy region, which at 10 keV is presently of a few counts per kg per keV per day.

With the R&D activity carried out in Hall C substantial improvements have been obtained with arrays of four of the same crystals to be used for CUORICINO and CUORE (cubes of TeO2 with 5 cm side). The resolution in energy on gamma rays has surpassed already that of the crystals of the twenty crystal array, despite the larger mass due to the improved thermistor adopted. For alpha particles the resolution FWHM is of about 3.8 keV, the best in the world for any detector. Considerable effort has been devoted to decrease the background due to external and internal radioactivity: a reduction of an order of magnitude has been already achieved.

3. INFN contribution to the experiment in terms of manpower and financial support

- Manpower: 12 physicists and 4 technicians are involved almost equally in MIBETA and CUORE experiments
- The financial support for MIBETA in 2000 was of 509 ML

4. Number of publications in refereed journals: 3

5. Number of talks to conferences: 3

6. Number of undergraduate and doctoral thesis on the experiment:

- n.1 Ph.D.;
- n.4 Laura diplomas

7.Leadership of the experiment

- A member of the group is the spokesman of the experiment.
- Most of the cryogenic activity and of the measurement of the radioactive background is carried out in Milano and in Gran Sasso
- The Milano group is the only one involved in development of data acquisition and electronic read-out for arrays of cryogenic detectors

8.Innovative instruments:

- As mentioned before the presently operating array is by large the most massive cryogenic set-up in the world
- The alpha particle resolution obtained with the large crystal of tellurides is the best of the ones obtained with any type of detector

9.Competing experiments

- There are only four other groups so far operating massive detectors underground and none of them searches for beta decay
- The Milano group is the only one to perform gamma spectroscopy at high energy and alpha spectroscopy with thermal detectors

10.International committee which has reviewed the experiment

The experiment has been reported and approved by the International Scientific Committee of the Gran Sasso Underground Laboratory and by the funding authorities of INFN and DOE (for the Berkeley group)