Next Generation Double-Beta Experimints:CUORE/CUORICINO and Majorana

University South Carolina Research Foundation, Columbia SC

Investigators

Abstract

The fundamental question of neutrino mass is important in cosmology, the study of the evolution of the universe, and for the completion of a theory of elementary particles. Neutrinos are the most prolific particles in the universe, and only since 1998 has it been established that they have any mass at all. It has now been well established experimentally, that in traversing from the sun to earth, and those created in our upper atmosphere, do change from one type to another, which requires that they do have mass. Determining their mass may also determine if they could account for part of the dark matter (sometimes called the missing mass of the universe). These experiments called neutrino oscillation experiments; however, cannot tell us how much mass they possess, just that their masses are not zero. There are two methods to directly determine the masses of neutrinos. In the first method, a precision measurement is made of the energy spectra of beta particles from radioactive decay of light nuclei. The deviation from the canonical theoretical shape of the energy spectrum near the high-energy end is a measure of the mass of the electron-type neutrino. These experiments are very difficult and are somewhat limited in mass sensitivity. Nevertheless, within their range of sensitivity, they are very valuable. In the case that neutrinos are their own anti-particles, there is an exotic radioactive decay called neutrinoless double-beta decay, that would be far more sensitive to neutrino mass. In addition, establishing by direct observation that this process exists, would prove that neutrinos are their own anti-particles. This in itself is extremely important for completing the theory of elementary particles. It would also support specific models of the very early universe that explain why the universe is almost completely particles at present, with almost no anti-particles. Without some small excess of particles over anti-particles in the very early universe, we ourselves, and all we see, could not exist today. The projects CUORE and Majorana are both large, next generation neutrinoless double beta decay experiments. They are being designed to probe a mass range a factor of ten more sensitive than presently exists from three experiments, two of which the PI of this grant participated in with leadership roles. The Majorana experiment is a proposed 500 kg array of high purity Ge detectors, isotopically enriched in 76Ge, the candidate parent double beta decay nucleus. It involves five national laboratories and eight universities. It would be built in the US with US technology. I involves many graduate students and will be a prolific source of PhD thesis material. There are a number of spin-off technologies useful in nuclear weapon non-proliferation and in homeland defense. CUORE is a proposed 750 kg array of cryogenic detectors of tellurium oxide to search for the neutrinoless double-beta decay of the isotope 130Te. It is a collaboration between Italy and the US, and is being constructed in the Gran Sasso National Laboratory in Assergi, Italy. It is a new technology because of its mass. It offers the same kind of educational opportunities as does Majorana, and is training US graduate students and post doctoral scientists in the technology of very large cryogenic detectors that do not exist in the US.