Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session JG: Techniques for Neutrino Science |
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Sponsoring Units: DNP JPS Chair: John Wilkerson, University of Washington Room: Ritz-Carlton Hotel Plantation 2 |
Thursday, September 22, 2005 9:00AM - 9:15AM |
JG.00001: Assessing the quality of waveforms from the neutral current detectors in the final phase of the Sudbury Neutrino Observatory experiment Nikolai Tolich The Sudbury Neutrino Observatory (SNO) has recently started its third experimental phase with the deployment of $^3$He proportional counters throughout the detector. These proportional counters allow event-by-event separation of neutral current and charged current events. Oscilloscopes connected to these proportional counters record the waveforms, which can be used to distinguish alpha background events from neutron signals. Some of the acquired waveforms are instrumental noise that needs to be removed. I will present results on the identification of these noise events, and the general quality of the waveform data. [Preview Abstract] |
Thursday, September 22, 2005 9:15AM - 9:30AM |
JG.00002: SNO Neutral Current Detectors: Electronic Calibration Gersende Prior The Sudbury Neutrino Observatory (SNO), in Ontario, Canada, has provided in the last few years results favoring neutrino oscillations as an explaination for the deficit observed in measuring the solar neutrino flux. The Neutral Current Detector array, which consists of 36 $^3He-CF_4$ and 4 $^4He-CF_4$ vertical counters arranged symmetrically around the center of the heavy water target, has been deployed recently. Two years of data taking would accumulate enough statistics for an improved measurement of the total solar neutrino flux. In order to best understand data provided by this new set of detectors, electronic calibration are performed on a regular basis. The electronic calibration program consists both of a dedicated calibration campaign, where the electronic circuitry from the analogic to the digital conversion is probed by sending a pulse signal, and regular calibration data taking for electronic and detector performance monitoring. In this talk, electronic calibrations will be discussed with specific attention to the determination of the ballistic deficit, which produces correlations between pulse amplitude and duration in shaping amplifiers. [Preview Abstract] |
Thursday, September 22, 2005 9:30AM - 9:45AM |
JG.00003: Neutrons, a Trouble-Maker for Double-Beta Decay and Dark Matter Experiments Andrew Hime, Dongming Mei Neutrons and neutron-induced cosmogenic radioactivity are an important background for underground experiments in rare events search for double-beta decay and dark matter. The problem of neutron-induced cosmogenic activation at sea level in materials is studied. We perform a Monte Carlo simulation to evaluate the neutron-induced background underground for double-beta decay and dark matter experiments. The ($\alpha$,n) neutrons are studied in terms of the radio-purity of rock composition and muon-induced neutrons are evaluated according to the depth. The shielding of ($\alpha$,n) neutrons as a function of thickness of polyethylene is modeled. The correlation of the underground muon flux seasonal variation and the annual modulation signal for dark matter experiments is examined. We present a depth-sensitivity relation (DSR) for underground experiments. [Preview Abstract] |
Thursday, September 22, 2005 9:45AM - 10:00AM |
JG.00004: Radioactive background studies for the CUORE neutrinoless double beta decay experiment Michelle Dolinski The proposed CUORE experiment will use an array of $\sim$1000 TeO$_2$ bolometers to search for neutrinoless double beta decay at the Gran Sasso Laboratory in Italy. The currently operating Cuoricino experiment, with 62 bolometers, is both a prototype for CUORE and an independent neutrinoless double beta decay experiment. In order for CUORE to reach a five year sensitivity on the effective neutrino mass on the order of 30 meV, a background of less than 0.01 counts/keV/kg/y in the double beta decay region is needed. We have examined the contributions to the radioactive background from copper, TeO$_2$ powder, and the teflon that supports the crystals and provides a weak thermal link to the cold reservoir. In particular, we have used neutron activation analysis and low background gamma ray spectroscopy to determine the concentrations of uranium and thorium in the teflon used in Cuoricino. In this talk, we will present our findings. [Preview Abstract] |
Thursday, September 22, 2005 10:00AM - 10:15AM |
JG.00005: Background Reduction in the Majorana Neutrinoless Double-Beta Decay Experiment. Reyco Henning Majorana is a proposed, scalable, 180-kg array of enriched germanium crystals that will search for neutrinoless double-beta (0\textit{$\nu \beta \beta $}) decay in $^{76}$Ge. The focus of this talk is the reduction of backgrounds in Majorana, a vital aspect of any low-background experiment. The first step is identification of possible backgrounds, including radioactive contamination in the detector and cosmic-ray induced backgrounds. The next step is estimating background reduction from mitigating techniques, including ultra-pure material manufacturing, shielding, detector granularity, crystal segmentation, pulse-shape analysis, time correlations, and underground manufacturing and operation. Finally, all these components are assembled into a background model. With this background model, we are confident we can improve the current half-life limit of 0\textit{$\nu \beta \beta $} decay in $^{76}$Ge from 2 x 10$^{25}$ years to about 5.5 x 10$^{26}$ years, in the absence of a 0\textit{$\nu \beta \beta $} decay signal. [Preview Abstract] |
Thursday, September 22, 2005 10:15AM - 10:30AM |
JG.00006: Pulse Shape Analysis in Segmented Detectors as a Technique for Background Rediction in Ge $\beta$$\beta$ Decay Experiments Victor M. Gehman The immense improvement in the sensitivity of $\beta$$\beta$ decay experiments has led to the need to use a variety of advanced signal processing techniques to further reduce experimental backgrounds. These techniques are primarily concerned with discerning single-site from multiple-site energy depositions. One such technique especially effective when using Ge detectors (for experiments utilizing $^{76}$Ge as a $\beta$$\beta$ decay source) is pulse shape analysis. An exciting extension to this technique is the inclusion of detector segmentation. We present current status and results in support of the Majorana Project (a proposed next-generation $\beta$$\beta$ experiment using a large array of 86\% enriched $^{76}$Ge crystals as both source and detector), in which we study the effectiveness of this combination in discriminating between single and multiple-site energy depositions on an event-by-event basis. We performed this work using a commercial detector from Canberra known as a ``Clover'' (a Clover is a close-packed array of four 800g, two-fold segmented natural germanium detectors) on our test bench at Los Alamos National Laboratory. We report on our efficiency in distinguishing between single and multiple-site energy deposition as well as estimates of our effective spatial resolution using these techniques. [Preview Abstract] |
Thursday, September 22, 2005 10:30AM - 10:45AM |
JG.00007: Muon-Induced Production of $^{16}$N Noah Oblath The Sudbury Neutrino Observatory (SNO) is a 1000-tonne heavy-water Cherenkov neutrino detector located in Sudbury, Ontario, Canada. Cosmic-ray muons pass through SNO at a rate of approximately 2.6 per hour, and they are easily vetoed. However, muon-induced spallation products with long lifetimes represent a background that must be considered. In particular, $^{16}$N can be produced by (n,p) and ($\mu^-$,$\nu_{\mu}$) reactions on $^{16}$O. The $\beta^-$ decay of any $^{16}$N ($T_{1/2}=7.13$~s, $Q = 10.44$~MeV) in the heavy water would represent an important background in SNO's neutrino measurements. We have investigated the production of $^{16}$N by muons in the salt phase of the SNO experiment and found an initial $^{16}$N activity in the 391-day salt-phase dataset consistent with zero: $-0.97\pm1.3$~kton$^{-1}$. The result will be compared with theoretical expectations. [Preview Abstract] |
Thursday, September 22, 2005 10:45AM - 11:00AM |
JG.00008: Full-Volume Calibration of KamLAND and Precision Measurement of Oscillation Parameters Karsten M. Heeger The Kamioka Liquid scintillator Anti-Neutrino Detector (KamLAND) has measured the flux of anti-neutrinos from nearby nuclear power plants in Japan and made the first observation of the disappearance of reactor $\overline{\nu}_{e}$. Recent measurements by KamLAND show evidence of spectral distortion, a clear sign of neutrino oscillation, and provide the most precise determination of the oscillation parameter $\Delta m^2_{12}$. KamLAND's measurement of neutrino oscillation parameters is currently limited by systematics, primarily the determination of the fiducial volume. Calibrations throughout the entire detector volume are required to fully exploit KamLAND's physics potential. This talk will describe the development of a novel calibration system and the expected improvements to KamLAND's measurement of $\overline{\nu}_{e}$ oscillation parameters. [Preview Abstract] |
Thursday, September 22, 2005 11:00AM - 11:15AM |
JG.00009: Understanding KamLAND's Detector Response: Instrumentation forKamLAND's Full-Volume Calibration System Lindley Winslow The KamLAND collaboration has developed a novel deployment system forthe positioning of radioactive calibration sources throughout theentire fiducial volume of the detector. This calibration device uses avariety of systems including inclinometers, pressure sensors, and theimaging of infrared LEDs to monitor its position. The calibrationsystem is also fitted with several low-activity Co/$^{60}$ sourcesthat will allow us to reconstruct its position using photomultipliertube information. The combination of these methods will provide anaccuracy of $\sim$2cm in the calibration source position. Mapping thevertex reconstruction bias throughout the detector volume is essentialfor reducing the fiducial volume uncertainty and improving theabsolute $\overline{\nu}_{e}$ flux measurement. Further studies of thedetector's energy scale and response will help with the measurement ofthe observed spectral distortion and the associated oscillationparameter $\Delta m^2_{12}$. [Preview Abstract] |
Thursday, September 22, 2005 11:15AM - 11:30AM |
JG.00010: Spallation-Induced Backgrounds in the KamLAND Detector Daniel Dwyer The KamLAND detector provides a good environment for the study of low-energy backgrounds due to the interaction of cosmic ray muons with the detector material. At 2700 m.w.e overburden a muon rate of 0.3\,Hz is measured in the main detector. The rough rates of $\sim$3000 spallation neutrons, $\sim$60 $^{12}$B/$^{12}$N, and $\sim$1.5 $^{9}$Li/$^{8}$He per kton-day are measured. The contribution of $^{12}$N is $\sim$1\% and $^{8}$He is limited to less than 15\% at 90\%\,C.L. The ongoing studies of these backgroungs will be discussed. [Preview Abstract] |
Thursday, September 22, 2005 11:30AM - 11:45AM |
JG.00011: Event Identification In SNO's NCD Phase G. Adam Cox In the final phase of SNO, the rate of the total solar neutrino flux can be measured using event-by-event particle identification of events recorded by the newly installed Neutral Current Detectors (NCDs). The NCDs are an array of $^{3}$He proportional counters constructed mostly from ultra-pure nickel tubes that capture neutrons produced by the neutral-current interaction between solar neutrinos and the deuterium in SNO's heavy water. The product of the neutron capture is a back-to-back proton and triton pair which ionize the proportional-counter gas and generate a current on the anode. In order to extract the rate of neutral-current interactions, neutron signals in the NCDs must be distinguished from events caused by ionizing alphas from the decay of U and Th embedded in the NCDs and electronic discharges. Calibration and characterization of the NCD electronics are essential to event identification. The current status of this effort and the role of the NCD electronics calibration will be discussed. [Preview Abstract] |
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