The measurement of the neutrino masses and their properties is still an unresolved question in Astroparticle Physics and has several implications in particle physics and in understanding the evolution of the Universe. Neutrinos plays an important role in the primordial nucleosynthesis and in the evolution of the Universe. Violation of the lepton number conservation will indicate the need of models beyond the Standard Model. The neutrinoless double beta decay (0nuDBD) plays an important role in this research because allow the determination of the behaviour of the neutrino as a Majorana particle and the measurement of its mass. The decay rate, in fact, is proportional to the mass-squared of the electron neutrino. At present cryogenic bolometers or germanium diodes are in operation in the 0nuDBD research. With these techniques an active mass of about 100-200 kg and a sensitivity of about 40-100 meV can be achieved. This sensitivity is limited to the degenerate mass region, partially covering the inverse hierarchy region. The direct hierarchy region, in which the electron neutrino mass is 5-10 meV or less, is still unreachable. These techniques based on crystals require a radioactive background reduction which is based on the detection of hybrid bolometric-scintillation signals or Cherenkov light that will be carried out by the research units involved in the present project. The main difficulty, however, is the construction of detectors with an active mass two orders of magnitude larger.
The main purpose of this experimental activity is to overcome the difficulties related to the construction of large size experiments based on crystals following the idea proposed in middle 90’s by R. Raghavan. By exploiting the excellent characteristics of radio purity of an organic scintillator, an experiment for the detection of the 0nuDBD based on Xe-136 dissolved in the scintillator can be realized. Since the solubility of the gaseous Xenon in standard condition is about 20 g/lit and assuming a radioactive background mainly due to the Th-232 chain, Ragavan and collaborators demonstrated that the sensitivity of 10**27 y can be achieved by dissolving about 1.3 t of enriched Xenon in 100 mc of liquid organic scintillator.
Therefore the project aims to demonstrate the feasibility of the construction of a large-size third-generation 0nuDBD experiment, with an active mass of about 15 t, radioactive background in the 10-6 c/kg/y and energy resolution at the double beta peak better than 1.5 %.
People involved in this activity: F. Budano, S. Bussino, M. De Vincenzi, S.M. Mari