Neutrinoless Double Beta Decay and Lepton Number Violation

Neutrinos have no charge why they could be their own antiparticles, called Majorana particles. In the standard model neutrinos were supposed to be massless, but from measurements of neutrino oscillations we know neutrinos have mass. Neutrino masses are surprisingly small compared to the mass of all other fermions. To understand the smallness of neutrino masses in theory, it is favored to assume a Majorana character for neutrinos. Since this results in lepton number violation, it would at the same time be a potential mechanism to produce the matter-antimatter asymmetry in the Universe. That is why it would be very attractive to prove the Majorana character of neutrinos experimentally. The simplest but not simple method is to search for neutrinoless double beta decay. So far, no signal for neutrinoless double beta decay has been observed. Worldwide many experiments try this with different detection methods: liquid noble gases, liquid scintillators, low temperature calorimetry or semiconductors. All trying to reduce background as much as possible with the goal to achieve the highest possible sensitivity.