Neutrinoless double beta decay (0νββ) is a powerful tool to investigate Lepton Number Violation (LNV), and the only practical way to assess the nature of the neutrinos. It can therefore provide unique information about the Physics Beyond the Standard Model.

Neutrinos, some of nature’s weirdest fundamental particles, are nearly massless—emphasis on nearly. They were predicted to be completely massless, but experiments roughly 20 years ago found they surprisingly do have some mass.

Neutrinos are born in various decays, which is when a particle changes from one type into another. In a beta decay, a neutron (made of one up quark and two down quarks) can transform into a proton (made of two up quarks and one down quark), an electron, and an electron antineutrino.

In order for (double) beta decay to be possible, the final nucleus must have a larger binding energy than the original nucleus. For some nuclei, the process occurs as conversion of two protons to neutrons, emitting two electron neutrinos and absorbing two orbital electrons (double electron capture).

The antineutrino (or anti-neutrino) is a lepton, an antimatter particle, the counterpart to the neutrino. Actually, there are three distinct antineutrinos, called types, or flavors: electron antineutrino (symbol ̅νe), muon antineutrino (symbol ̅νμ), and tau antineutrino (symbol ̅ντ).

Boson is the name for a generic class of particles. The Higgs boson is one (if it exists) but so are many other particles. are bosons. Quarks, electrons and neutrinos, on the other hand, are fermions.

In particle physics, a lepton is an elementary particle of half-integer spin (spin 1⁄2) that does not undergo strong interactions. Two main classes of leptons exist: charged leptons (also known as the electron-like leptons or muons), and neutral leptons (better known as neutrinos).