First results on neutrinoless double beta decay of 130Te with the calorimetric CUORICINO experiment

The first results are reported on the limit for neutrinoless double decay of Te-130 obtained with the new bolometric experiment CUORICINO. The set-up consists of 44 cubic crystals of natural TeO2, 5 cm on the side and 18 crystals of 3 x 3 x 6 cm(3). Four of these latter crystals are made with isotopically enriched materials: two in Te-128 and two others in Te-130. With a sensitive mass of similar to40 kg, our array is by far the most massive running cryogenic detector to search for rare events. The array is operated at a temperature of similar to10 mK in a dilution refrigerator under a heavy shield in the Gran Sasso Underground Laboratory at a depth of about 3500 m.w.e. The counting rate in the region of neutrinoless double beta decay is similar to0.2 counts keV(-1) kg(-1) y(-1), among the lowest in this type of experiment. No evidence for neutrinoless double beta decay is found with the present statistics obtained in about three months with a live time of 72%. The corresponding lower limit for the lifetime of this process is of 5.5 x 10(23) years at 90% C.L. The corresponding limit for the effective neutrino mass ranges between 0.37 to 1.9 eV depending on the theoretically calculated nuclear matrix elements used. This constraint is the most restrictive one except those obtained with Ge diodes, and is comparable to them. (C) 2004 Elsevier B.V. All rights reserved.