Neutrinos are amongst the most abundant particles in the Universe and yet we do not know many of their properties. For example, we do not know their absolute mass scale or their particle-antiparticle nature. Because of their abundance, even a small mass could have far-reaching consequences for understanding their role in the evolution of our Universe. Knowing if neutrinos are their own antiparticles could have implications in understanding the matter-antimatter asymmetry of our Universe.
Neutrino-less double beta decay (NLDBD) experiments address these two fundamental questions. Double beta decay is a rare nuclear decay that has been measured in several nuclei when it is energetically favorable. Some nuclei are stable against ordinary beta decay but are unstable for double beta decay in which two neutrons in the nucleus are simultaneously converted to protons and two electrons are emitted. Double beta decay can proceed through several modes. The experimentally measured process, the two-neutrino mode in which two electron antineutrinos are also emitted, is completely described by known physics. NLDBD is an as-yet-undetected decay that involves no neutrinos in the final state and necessarily would indicate that neutrinos are their own antiparticle. The rate of such decays determines the scale for the effective neutrino mass.
The CUORE (Cryogenic Underground Observatory for Rare Events) experiment at the Gran Sasso laboratory (LNGS), Assergi, Italy, is one of the next generation experiments to search for NLDBD. It uses the 130-Te isotope with a design sensitivity to the effective neutrino mass ranging between 40-70 meV, depending on nuclear structure calculations. The UCLA group's major hardware responsibilities include the testing of all the front-end electronics and the installation and commissioning of the electronics system at LNGS in collaboration with the Milan and South Carolina groups. Their analysis focus will be on understanding of the residual background sources through Monte Carlo simulations.
The technology being used in CUORE which is based on milliKelvin bolometry is one of the most innovative and largest scale in the field. If their electronics proves out as designed, it will likely influence other fields. The NLDBD experiments address fundamental physics issues that have a scientific impact beyond particle and nuclear physics. For example, if neutrinos are Majorana particles and neutrino masses are from the See-Saw Mechanism, the lepton sector could violate CP (Charge-Parity) symmetry and contribute to the matter and anti-matter asymmetry of the Universe. The group will also help train undergraduate and NSF-REU students in their research programs and provide them with research experiences in neutrino physics and modern detector technology.
