Session B13: Minisymposium on Nuclear Physics Deep Underground I

Going Deep - Nuclear Science Underground

The creation of a Deep Underground Science and Engineering Laboratory (DUSEL) at the Homestake Mine in South Dakota as well as the construction of SNOLAB in Sudbury, Ontario provide exciting new opportunities for the nuclear science community. The proposed next generation of underground experiments to be sited at these facilities aim to investigate a broad set of fundamental questions: What is the nature of neutrinos? Can we directly detect dark matter? How did the elements originate? What nuclear reactions are important to stellar evolution and dynamics? How did the matter - antimatter asymmetry we observe in the universe arise? Answers to these questions impact not only nuclear physics, but particle physics, astrophysics, and cosmology. There are numerous technical challenges that need to be met, including attaining unprecedented levels of material purity, developing ultra-sensitive assay techniques, and improving our understanding of nuclear properties. Likewise there are a number of interesting theoretical issues that need to be addressed including improving our knowledge of nuclear matrix elements and understanding the limits of nuclear stability. This talk with give an overview of the physics, the experiments, and the technologies that will help us reach a better view of our universe by going deep underground.   

EXO-200 Status

EXO-200 (Enriched Xenon Observatory-200 kg) is an underground double-beta decay experiment that uses 200 kg of Xenon isotopically enriched to 80{\%} in Xenon-136. The Xenon is contained in an ultra-low background TPC where there is simultaneous collection of scintillation light (using Large Area Avalanche Photodiodes (LAAPD's) ) and ionization charge in order to significantly enhance the energy resolution. EXO-200 should measure the, as yet unobserved, two neutrino double-beta decay mode as well as achieve competitive sensitivity for the neutrinoless double-beta decay mode of Xenon-136. EXO-200 was moved from Stanford University in August of 2007 and is currently under a 2000 meter water-equivalent overburden at the WIPP site in New Mexico.   

Development of barium tagging technology for EXO

The Enriched Xenon Observatory (EXO) is a series of experiments designed to search for the neutrinoless double beta decay of Xenon-136. The first experiment, known as EXO-200, is comprised of a liquid xenon TPC containing 200 kg of xenon enriched to 80{\%} in Xenon-136 and is nearing completion. To suppress possible radioactive backgrounds, the EXO collaboration is also pursuing the development of a new technique to identify the production of the barium daughter ions produced by double beta decay. For this purpose, a linear radio-frequency ion trap has been constructed. Individual barium ions are trapped in this helium or argon buffer gas-filled trap and observed with a high signal-to-noise ratio by resonance fluorescence. Furthermore, two ion transfer methods are under parallel development, both involving the capture and transport of the ions on the surface of a specially designed tip. This talk will present the results obtained in the trapping of single buffer gas-cooled barium ions and the transfer of ions using a cryogenic tip, and our plans for an ion transfer tip using resonance ionization spectroscopy.   

The M{\sc ajorana} Neutrinoless Double-beta Decay Experiment

Neutrinoless double-beta decay searches play a major role in determining the effective Majorana neutrino mass, the Majorana nature of neutrinos, and a lepton violating process. The M{\sc ajorana} experiment proposes to assemble an array of HPGe detectors to search for neutrinoless double-beta decay in $^{76}$Ge. Initially, M{\sc ajorana} aims to construct a prototype system containing 60 kg of Ge detectors to demonstrate the potential of a future 1-tonne experiment. The design and potential reach of the prototype system will be presented. This talk will also discuss material purity, detector optimization, background rejection, identification of rare backgrounds, and other key technologies to be utilized in the M{\sc ajorana} experiment.   

Methods for deploying ultra-clean detectors

Next-generation underground experiments, such as searches for neutrinoless double-beta decay and dark matter experiments, will perform high-sensitivity measurements that require extremely low backgrounds. The {\sc{Majo\-ra\-na}} Collaboration~\footnote{F.T. Avignone III (2007) arXiv:0711.4808v1} proposes such an experiment to search for neutrinoless double-beta decay using an array of germanium crystals enriched in $^{76}$Ge. The design of the {\sc{Majo\-ra\-na}} experiment must minimize backgrounds while meeting criteria for electrical signal quality, structural integrity, and thermal cooling characteristics. Recent work has addressed detector deployment in ultra low-background environments. Advances have been made in fabrication of radiologically pure copper parts. Prototype designs for detector support structures reduce backgrounds by minimizing component mass and making use of ultra-pure materials. This talk will describe the design and use of cryostat test-stands to investigate the performance of prototype designs for detector strings. While {\sc{Majo\-ra\-na}} uses germanium detectors, the design considerations and progress made by the collaboration are applicable to other detector technologies and fields of research.   

The development of LENS

The Low-Energy Neutrino Spectroscopy (LENS) Collaboration aims to precisely measure the entire energy spectrum of solar neutrinos, including low-energy neutrinos from $p+p$ fusion, through charged-current neutrino interactions on indium in real time. Such a measurement would provide important insights into our understanding of the sun and of neutrino properties. To achieve this goal, we have developed a detector design based on a large, highly-segmented volume of liquid scintillator, which we call the {\em scintillation lattice}. The spatial segmentation of the scintillation lattice allows even low-energy neutrino interactions to be distinguished from background sources. We are currently constructing an approximately 1 m$^3$ prototype instrument, {\em miniLENS}, that will demonstrate the detector performance and determine the optimum route to scale to an $\approx 200$~ton instrument. The detector design, the status of the R\&D program, and plans to deploy a full-scale instrument underground will be discussed.   

Metal Loaded Organic Liquid Scintillator for the LENS Experiment

LENS is a low energy neutrino experiment that will measure the solar neutrino spectrum above 114keV which accounts for $>$95{\%} of the solar neutrino flux. It will allow us to measure the solar luminosity in neutrinos, test the current LMA-MSW oscillation model independently from solar models, probe the temperature profile of solar energy production, as well as search for sterile neutrino oscillations using an artificial neutrino source. The experimental tool is charged-current capture of the neutrino on In115, with prompt emission of an e- and delayed emission of 2 gamma rays that serve as a time/space coincidence tag. LENS requires $\sim $10 tons of Indium be loaded into 100,000 liters of organic scintillator (pseudocumene, linear alkylbenzene) via liquid-liquid extraction. Results of several years of development will be described. The key properties of the Indium scintillator are: high metal loading (8-10{\%}), long attenuation length at 430nm ($>$8m), high scintillation yield, stability on the scale of years.