Recent years have seen a proliferation of experiments based on the liquid noble gas detector technology. Noble gases are an attractive medium for particle detectors due to their low ionization potential, high scintillation efficiency, long electron lifetime and low cost. These detectors are currently employed to address a wide variety of fundamental physics questions, including neutrinoless double beta decay, neutrino oscillations, rare muon decays, dark matter searches and solar neutrinos. Many of these questions are central to the scientific mission of an underground lab and similar detectors have been proposed for the initial suite of experiments at DUSEL.
Most liquid detectors to date are of relatively modest size, with target masses ranging from a few kilograms to a few hundred kilograms. However, next-generation experiments are poised to push the boundaries far beyond the current state of the art. For an experiment to succeed in this new regime, it will be necessary to purify the cryogenic liquids far beyond what current technologies have achieved. For existing TPC-style detectors, the concentration of electronegative impurities must be less than about 100 ppt oxygen equivalent to avoid attenuation of the charge signal as it drifts through the detector volume. Therefore, the next set of experiments will require impurity concentrations from one to ten ppt, or free electron lifetimes from tens to hundreds of milliseconds.
This award will enable the group to develop a new method for detecting extremely low concentrations of impurities, with the potential to extend current sensitivities by several orders of magnitude.
As part of the Broader Impacts of this work, this impurity detector would find wide application for many of the fundamental physics experiments which are likely to be hosted by DUSEL. In addition, this work will also have significantly broader impact by serving to further the education of graduate students.
This award supported our development of new experimental techniques which can be applied to neutrino physics and dark matter searches. Neutrinos are the lightest and most elusive of the fundamental particles which are known to exist, while the exact nature of dark matter is still unknown. Studying these phenomena in the laboratory requires highly sensitive detectors, capable of indentifying just a handful of important interactions per year, while rejecting interactions due the much more common and well-understood types of radioactivity. Among the most important requirements for these detectors is that the detector material should be highly purified. But to achieve a high degree of purity, we must first develop methods to measure the purity. With this award we developed several new techniques which have extended the sensitivity of purity analysis for xenon gas and argon gas by a factor of 10,000 to one million. Xenon and argon are common detector materials used for neutrino and dark matter experiments, and our methods have already been adopted by several experimental collaborations working in this area. These experiments include the EXO-200 experiment, which is studying the fundamental nature of neutrino mass, and the LUX dark matter experiment, which is attempting to observe component particles of the Milky Way's dark matter halo. These two experiments are among the most sensitive in their respective fields, and this sensitivity has been achieved in part by application of the methods which we developed under this award.
