The CUORE Experiment: An Observatory for Neutrino-Less Double Beta Decay

Abstract

The Standard Model (SM) of particle physics is a theory that aims at the description of every phenomenon of nature in terms of the properties and interactions of the microscopic constituents of matter: the elementary particles. Despite its great success, continuously confirmed by experimental evidences and measurements across many decades, nowadays it is clear that in a small number of cases the SM description is oversimplified, and an extension of the theory is mandatory in order to explain the most recent experimental observations. Among the elementary particles included in the model, neutrinos, the neutral “brothers” of electrons, muons and tau leptons, are definitely the most elusive. At the same time they are characterized by peculiar behaviors that can hardly be accommodated in the SM picture. Since more than one decade the neutrinos are known to have a tiny, but not vanishing, mass. This property, demonstrated by observing the oscillating behavior of their leptonic flavor, cannot be explained within the SM, where neutrinos are massless by construction. In order to include the neutrino mass, the theory has to be modified and the neutrino nature itself is put into discussion: in the SM all the fermions, that is, the particles that make up the matter (as opposed to bosons that are responsible for the interaction between fermions), are Dirac particles. Dirac particles are different from their own anti-particles (i.e., the equivalent constituents of anti-matter). For massive neutrinos, however, this is not necessarily true: they could be, unique in nature, Majorana particles, meaning that they could be identical and indistinguishable from their anti-matter counterparts. In this case, some new, unforeseen phenomena could occur outside the predictions of the Standard Model.