How to improve the sensitivity of future neutrino mass experiments with thermal calorimeters

Abstract In this paper we discuss the perspectives for a new generation of neutrino mass experiments using thermal detectors to reach interesting sensitivities before and after the KATRIN experiment. By scaling the performance of the present Milano neutrino mass experiment with Monte Carlo simulations, we show how a new experiment can validate the present limit of few eV set by spectrometers before the KATRIN experiment starts. We also show how such a result can be used to design a very large thermal detector experiment to reach sensitivities beyond the KATRIN expected one

Gamma ray spectroscopy with high-Z thermal detectors

Abstract A massive thermal detector to be used to search for rare decays and to detect high-energy γ-rays has been operated both at sea level and underground. It consists of a 20.9 g monocrystal of TeO 2 whose temperature is measured by means of a neutron transmutation doped thermistor. The detector was first operated in Milano at a base bolometer temperature of 22.5 mK and with a FWHM resolution of 90 keV, rather independent of the γ-ray energy. Much better results have been obtained when the detector was operated underground, under a suitable shielding against local radioactivity and inside a Faraday cage. The base bolometer temperature could be as low as 14.5 mK which, together with the elimination of pile-up, allowed to achieve FWHM resolutions of 1% for γ-rays above 2.0 MeV. The increase in the base temperature of the bolometer when exposed to a weak radioactive source is discussed in view of possible applications in the search for dark matter

Large calorimetric devices for double beta decay and dark matter

Abstract The use of cryogenic thermal particle detectors permits the realization of detectors of various compositions, various sizes and very good energy resolution. In particular these characteristics are very promising for the realization of double beta decay and dark matter search experiments. Our group is mainly interested in the study of double beta decay of 130Te and 116Cd. For tellurium we have realized various detectors using TeO2 crystals, the final one with a mass of 334 g. For cadmium a CdWO4 crystal of 58 g has been used in various tests. The double beta decay measurement has been performed in the Gran Sasso Underground Laboratory. Measurements on the 334 g TeO2 crystal have been performed for 3000 h. Detector resolution is around 10 keV FWHM and the internal contamination of 238U and 232Th in the crystal is of the order of 10−13 g/g. A lower limit on the half-life of neutrinoless double beta decay for 130Te of 8.2 × 1021 yr (90% CL) is measured. The test measurements of CdWO4 reach an energy resolution of about 5 keV FWHM with a very high efficiency to gamma ray detection. A limit on the neutrinoless channel of 7 × 1019 yr (90% CL) is evaluated in 340 h. In this test an end point energy of 318.8 ± 1.4 ± 5 keV and a half-life of (9.3 ± 0.5 ± 1) × 1015 yr for the beta decay of 113Cd are also measured. The last part of the paper is dedicated to a brief discussion of our proposal for the solar neutrino flux measurement and for the search of dark matter using cryogenic detectors

A search for neutrinoless double beta decay of 130Te with a thermal detector

Abstract A 73.1 g TeO2 bolometric detector has been operating for more than two months at about 16 mK in a specially constructed low activity dilution refrigerator installed in the Gran Sasso Underground Laboratory and shielded against environmental radioactivity. Its energy resolution is comparable with that of a Ge diode. A spectrum of the thermal pulses collected in 1389 h of effective running time shows no evidence for neutrinoless double beta decay of 130Te. The corresponding lower limit of the lifetime is three orders of magnitude more stringent than those obtained for the some nucleus with conventional techniques. It also exceeds the value for the inclusive (two neutrino and neutrinoless) lifetime obtained by geochemical searches. Double beta decay of 130Te has therefore to be attributed mainly to the two neutrino channel

Large mass, low temperature, low background detectors

Abstract Bolometric detectors can be realized with a wide range of materials, and large mass. Some aspects regarding the energy resolution of large bolometers are analyzed. Preliminary experimental results on neutrinoless ββ decay of tellurium, obtained with this technique, are shown

Optimization of Si-Implanted Thermistors for High Resolution Calorimeters to be used in a Neutrino Mass Experiment

A procedure of optimization of Si-implanted thermistors was started, with the final aim to develop bolometers with a resolution of a few eV in the keV range. The initial approach was to assume that a thermal decoupling between phonons and hopping electrons establishes inside the thermistors, with consequent reduction of the sensitivity and incomplete transfer of the particle generated phonons to the conduction electrons. This assumption however failed in explaining the collected experimental data, which can be described much more satisfactorily introducing an electric field dependance of the thermistor resistance. This alternative interpretation modifies the parameter choice for an optimum devic

Cryogenic thermal detectors as a powerful way to analyse internal activities

Abstract The Milano group is using an array of four crystals of TeO 2 , 334 g each, to search for neutrinoless double beta decay of 130 Te [A. Alessandrello et al., Phys. Lett. B 335 (1994) 519; Proc. 4th Int. Workshop on Theoretical and Phenomenological Aspects of Underground Physics — TAUP 95, to be published in Nucl. Phys. B (Proc. Suppl)]. The detectors are operating in a dilution refrigerator installed in the Underground National Laboratory of Gran Sasso specially built with low activity materials. Due to the low external background and the good energy resolution it is possible to obtain precise measurements of some internal contaminations of the detector itself. An analysis of a contamination of 210 Po and of the decay of 123 Te is presented

Preliminary results on double beta decay of 130Te with an array of twenty cryogenic detectors

Preliminary results on double beta decay of 130 Te obtained in the first run of an array of twenty cryogenic detectors are presented. The set-up is made with crystals of TeO of 340 grams each corresponding to the largest presently operating 2 cryogenic mass. It 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 90% c.l. lower limit of 5.6 = 10 22 years has been obtained on the lifetime for neutrinoless double beta decay of 130 Te in a preliminary test run, corresponding to about one week of effective running time. No evidence is also found for double beta decay to the first excited 2 q state of 130 Xe with a 90% c.l. lower limit of 1.7 = 10 22 years on that lifetime. Some consequences of the present results in th

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 scintillating bolometer for experiments on double beta decay

Abstract The scintillation yields of CaF 2 crystals with different doping concentration of Europium have been measured at low temperatures and their bolometric behavior has been investigated. After these studies we have constructed the first "scintillating bolometer" where the heat and scintillation pulses produced by charged particles are simultaneously recorded. With this method a strong suppression of the background from α -particles in the energy region of interest for searches on double beta decay of 48 Ca can be achieved