Advanced Techniques for Loading Metals into Liquid Scintillators

University Of Washington, Seattle WA

Investigators

Abstract

One of the most important questions regarding neutrino properties is whether or not neutrinos are their own antiparticles, or equivalently, whether neutrinos are Majorana rather than Dirac particles. If neutrinos are Majorana particles, the mechanism that gives them mass is not part of the Standard Model of particle physics and requires new physics. The most practical way to observe that neutrinos are Majorana particles is to see the neutrino-less double beta decay, a process that explicitly violates the conservation of lepton number. The work supported by this award will develop new techniques for increasing the concentration of metals that can be loaded into liquid scintillator detectors. The near-term physics goal is to improve the sensitivity of neutrino-less double beta decay searches with large underground liquid scintillator experiments, such as the SNO+ experiment. The sensitivity of SNO+ is a function of both the quantity of double beta decay Neodymium isotope that can be dissolved in the scintillator, and the detector's overall energy resolution: more isotope increases the signal, while improved resolutions allow better separation of signal from background. The limit to the total mass of isotope that can be dissolved comes from the competition between the additional statistics and the loss of light due to absorption by Neodymium. This work will carry out a dedicated investigation into the loading of Neodymium nanoparticles, rather than dissolving Neodymium directly, as a way to add more isotope while limiting the level of light lost, thus significantly improving sensitivity to a neutrino-less double beta decay signal. The plan of work includes development of loading techniques to ensure homogeneity and stability within the scintillator, measurements of optical transmission and scattering of the suspensions, measurements of light yield and scintillation timing profiles, and simulation and analysis to determine the impact of nanoparticle solutions on SNO+'s sensitivity to neutrino-less double beta decay. Broader Impacts The question of whether the neutrino is its own antiparticle is not only the most pressing question in neutrino physics, it also has implications for the origin of the current preponderance of matter over antimatter in our Universe. The techniques that will be investigated here can also be applied equally well to other liquid-scintillator detectors, including planned very large-scale detectors such as LENS. They may also be useful for the loading of any non-double beta decay isotope, for purposes that could go well beyond neutrino physics. The work described here will also play an important role in the training and education of young researchers. It is very well-suited to the involvement of undergraduates, both in hands-on activities as well as simple data analysis and simulation.