Bulletin of the American Physical Society
2009 APS April Meeting
Volume 54, Number 4
Saturday–Tuesday, May 2–5, 2009; Denver, Colorado
Session D10: Neutrino Physics II |
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Sponsoring Units: DNP Chair: Bill Louis, Los Alamos National Laboratory Room: Governor's Square 10 |
Saturday, May 2, 2009 3:30PM - 3:42PM |
D10.00001: Precision atomic masses for neutrinoless double-beta-decay and double-electron-capture Edmund Myers, Matthew Redshaw, Brianna Mount As currently understood, the definitive observation of neutrinoless double-beta-decay will imply that neutrinos are their own antiparticles (Majorana particles), while measurements of the decay rate, or limits on the rate, provide information on absolute neutrino mass. Large-scale neutrinoless double-beta-decay detectors, proposed or under development, such as EXO, CUORE, GERDA, MAJORANA, etc. should be sensitive to a linear combination of neutrino masses, the ``effective Majorana mass of the electron neutrino'', below 0.1 eV/c$^{2}$. The signature of neutrinoless double-beta decay is a sharp peak in the total electron-energy spectrum at the Q-value of the decay -- the mass-energy difference between the parent and daughter atoms. Using precision, cryogenic mass spectrometry, with one or two multiply-charged ions in a Penning trap, we have now measured the atomic masses of $^{136}$Xe, $^{130}$Te, $^{130}$Xe, $^{76}$Ge, $^{76}$Se to a fractional precision of 2 x 10$^{-10}$ or better, corresponding to Q-values with uncertainties below 25 eV. This is more than sufficient precision for the proposed large-scale experiments. Progress on mass measurements of $^{74}$Ge and $^{74}$Se, relevant to resonance-enhanced neutrinoless double-electron capture in $^{74}$Se, will also be reported. [Preview Abstract] |
Saturday, May 2, 2009 3:42PM - 3:54PM |
D10.00002: Double-Beta Decay of $^{150}$Nd to Excited Final States M.F. Kidd, J.H. Esterline, W. Tornow Studying $\beta\beta$ decay with emission of neutrinos (2$\nu\beta\beta$) in particular is important as a check for theoretical models which can be used to calculate the nuclear matrix elements for neutrinoless $\beta\beta$ decay (0$\nu\beta\beta$). These models are needed to obtain the effective electron neutrino mass from 0$\nu\beta\beta$ decay data. In QRPA models, the calculated matrix elements for transitions to the ground state and excited states depend in a different way on the so-called g$_{pp}$ parameter. Therefore, 2$\nu\beta\beta$ decay data to excited states are of special interest. Because SNO+ plans to use $^{150}$Nd as a nuclide in searches for 0$\nu\beta\beta$ decay, our goal is to measure the 2$\nu\beta\beta$ decay of $^{150}$Nd to the first excited 0$^+$ state in $^{150}$Sm. Only tentative information is available for $^{150}$Nd. Here we report our first 6 months of data collection using a 50 g enriched $^{150}$Nd$_2$O$_3$ (43 g $^{150}$Nd) sample placed between two high-purity germanium detectors. We search for the decay of $^{150}$Nd to the first excited 0$^+$ state in $^{150}$Sm by detecting the 334 keV and 406.5 keV deexcitation gamma rays in coincidence. Our apparatus is located at the Kimballton Underground Research Facility (KURF) which provides an overburden of 1450 m.w.e. Singles and coincidence spectra are shown and future plans are discussed. This work was supported by the U.S. Department of Energy, Office of Nuclear Physics under grant number DE--FG02--97ER41033. [Preview Abstract] |
Saturday, May 2, 2009 3:54PM - 4:06PM |
D10.00003: Double beta decay daughter ion detection on an optical fiber for EXO Brian Mong, Shon Cook, William Fairbank The EXO neutrinoless double beta decay experiment with $^{136}$Xe can be background free if the daughter, $^{136}$Ba, can be detected with high efficiency. This talk will present progress on a proposed single Ba$^+$ ion detection technique where the ion is drawn by electric fields and frozen on the tip of a cold optical fiber in the liquid Xenon TPC. The fiber guides excitation laser light towards the detection region and collects fluorescence back up the fiber. Experimental results on detecting small amounts of Rhodamine 6G dye molecules in solution and Ba atoms in solid Xe will be presented, along with preparations for studies of Ba$^+$ ions deposited with a mass-selected ion beam. [Preview Abstract] |
Saturday, May 2, 2009 4:06PM - 4:18PM |
D10.00004: The MAJORANA Demonstrator: An R\&D project towards a tonne-scale germanium neutrinoless double-beta decay search Reyco Henning The {\sc Majorana} collaboration is pursuing the development of the so-called {\sc Majorana} Demonstrator. The Demonstrator is intended to perform research and development towards a tonne-scale germanium-based experiment to search for the neutrinoless double-beta decay of $^{76}\mathrm{Ge}$. The Demonstrator can also perform a competitive direct dark matter search for light WIMPs in the $1-10\,\mathrm{GeV}/c^2$ mass range. It will consist of approximately 60 kg. of germanium detectors in an ultra-low background shield located deep underground at the Sanford Underground Science and Engineering Laboratory (SUSEL). The Demonstrator will test several different detector technologies, and half of the detector mass will be enriched germanium. This talk will review the motivation, design, technology and status of the Demonstrator. [Preview Abstract] |
Saturday, May 2, 2009 4:18PM - 4:30PM |
D10.00005: Surface-Alpha Backgrounds for HPGe Detectors in Neutrinoless Double-Beta Decay Experiments R.A. Johnson, T.H. Burritt, S.R. Elliott, V.M. Gehman, V.E. Guiseppe, J.F. Wilkerson The {\sc Majorana} Experiment will use arrays of enriched HPGe detectors to search for the neutrinoless double-beta decay of $^{76}$Ge. Such a decay, if found, would show lepton-number violation, confirm the Majorana nature of the neutrino, and help determine the effective Majorana neutrino mass. A potentially important background contribution to this and other double-beta decay experiments arises from decays of alpha-emitting isotopes in the $^{232}$Th and $^{238}$U decay chains on and near the surfaces of the detectors. An alpha particle emitted from the surface can lose energy within the dead region of a detector, depositing only a partial amount of its kinetic energy within the active region and possibly mimicking the signal from neutrinoless double-beta decay. Cleanliness, exposure to radon, detector design, and analysis techniques all contribute to the effect from surface alphas. Our experimental and simulation efforts to understand and mitigate surface alpha backgrounds for HPGe detectors will be presented. [Preview Abstract] |
Saturday, May 2, 2009 4:30PM - 4:42PM |
D10.00006: EXO-200 Status Steven Herrin EXO-200 (Enriched Xenon Observatory - 200 kg) is an underground double-beta decay experiment that uses 200kg 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 is currently under a 2000 meter water equivalent overburden at the WIPP site in New Mexico, where it is undergoing final construction and commissioning. [Preview Abstract] |
Saturday, May 2, 2009 4:42PM - 4:54PM |
D10.00007: The production of Ge-68 in Ge detectors due to fast neutrons V.E. Guiseppe, S.R. Elliott, V.M. Gehman, S.A. Wender A commercial HPGe detector was irradiated with neutrons at the Los Alamos Neutron Science Center for the activation of the radioactive isotope $^{68}$Ge and other isotopes that may be produced in Ge via cosmogenic-neutron reactions. The energy spectrum of the neutron beam used has a similar shape to cosmic-ray neutrons but at a much higher flux. Previous estimates of cosmogenic activation in Ge were affected by differing neutron fluxes used and the direct measurements were limited by the small production rate. This work benefits from the greater flux of neutrons to produce a large amount of $^{68}$Ge than that by cosmic-ray neutrons. Cosmic activation of $^{68}$Ge in Ge crystals is an expected background contribution to Ge-based neutrinoless double-beta decay experiments. A key to double-beta decay experiments is the mitigation of backgrounds to unprecedented levels. In the case of Ge-based experiments, backgrounds will be rejected making use of pulse shape analysis, detector segmentation and granularity, and event time correlation. Operation of the activated Ge detector provides a measurement the activation rate of several isotopes and a study of the effectiveness of some background rejection technologies. Identification and production rates of several cosmogenic isotopes will be presented. [Preview Abstract] |
Saturday, May 2, 2009 4:54PM - 5:06PM |
D10.00008: The Energy Calibration System for the CUORE Bolometric Double Beta Decay Experiment Samuele Sangiorgio CUORE, the Cryogenic Underground Observatory for Rare Events, employs an array of 988 TeO$_{2}$ bolometers to search for neutrinoless double beta decay ($\beta\beta0\nu$) in $^{130}$Te. The signature for $\beta\beta0\nu$ is a peak at the expected Q-value of 2530~keV in the summed energy spectrum of all detectors. In CUORE, bolometers are operated as perfect calorimeters and therefore a precise and reliable energy calibration is crucial for the success of the experiment. An innovative calibration system is being developed to provide energy calibration of all the detectors in the CUORE array. The project is particularly complex due to its integration in a unique low-temperature cryostat (detectors operate at 10~mK) and to the strict ultra-low background requirements of CUORE. We present the design, challenges and expected performances of this low-temperature calibration system. [Preview Abstract] |
Saturday, May 2, 2009 5:06PM - 5:18PM |
D10.00009: KArlsruhe TRItium Neutrino Experiment (KATRIN) detector and backgrounds Michelle Leber One of the more surprising discoveries of the past century is that neutrinos have non-zero mass, but measuring the absolute scale of the neutrino's mass has proven to be very challenging. The KArlsruhe TRItium Neutrino (KATRIN) experiment is dedicated to measuring or limiting the electron-type neutrino's effective mass. By analyzing the energy spectrum of electrons emitted in tritium beta decay, KATRIN is sensitive to masses as low as 0.20 eV with a 90$\%$ CL, an order-of-magnitude better than the current direct limit. KATRIN can achieve this sensitivity because of its highly luminous source, large acceptance Main Spectrometer with extremely accurate energy resolution, and efficient silicon detector with minimal backgrounds. Extensive Geant4 simulations of the silicon detector's intrinsic backgrounds were used to optimize the detector region design and indicate that these backgrounds are compatible with our projected sensitivity. The design goal is 1 mHz background in our region of interest for a 500 micron, 4.5 cm radius segmented silicon detector. For this experiment at the surface of the earth, the major backgrounds will be cosmic rays and natural radioactivity. Verification and results of simulations will be presented. [Preview Abstract] |
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