Neutrino Properties

Neutrino Properties

One of the most intriguing questions in physics today is, “Why is our universe matter dominated, and not antimatter dominated?” Neutrinos, although difficult to detect with their tiny masses, and no electrical charge, and oscillating flavors, could provide an insight.  Fundamental particles are of two types, Majorana or Dirac. Dirac particles are distinct from their anti-particles, however if a particle is Majorana, it is the same as its own antiparticle. If the neutrino is Majorana, this would demonstrate that lepton number is not a conserved quantity, and provides a mechanism that explains the matter-antimatter asymmetry in the universe. Furthermore, a Majorana neutrino would open the door to physics beyond the standard model.

Double-Beta Decay

In certain isotopes, “Two-neutrino” double-beta decay (2νββ) is allowed and involves the transformation of two neutrons into two protons with the emission of two electrons and two antineutrinos. If the neutrino is Majorana (it is its own antiparticle) a rare process, neutrinoless double-beta decay (0νββ), could occur. In this process, the two antineutrinos would annihilate within the nucleus before being emitted.  

In two-neutrino and neutrinoless double-beta decay experiments, only the electrons resulting from the decay are detected and their energies measured. In the case of 2νββ, these energies form a spectrum, as the energy is shared between the electrons and the antineutrinos. In the case of 0νββ, all the energy is carried away by the two electrons. Thus, the signature of such an event has the form of a peak at the end of the spectrum. The energy value of this peak is the total energy available for this process to happen.  

In order to have the potential to discover 0νββ, experiments must have large masses of source isotope, low radioactive backgrounds, and high efficiencies. Most experiments also operate deep underground to reduce the impact of cosmic rays. Experiments are assembled in clean rooms, and use shielding around the detector to achieve low radioactive backgrounds. Most experiments make the detector medium out of the same double-beta decay isotope to maximize efficiency.