Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session E14: Dark Matter II |
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Sponsoring Units: DPF Chair: Bernard Sadoulet, University of California, Berkeley Room: Hyatt Regency Jacksonville Riverfront City Terrace 10 |
Saturday, April 14, 2007 3:30PM - 3:42PM |
E14.00001: Quenching of Nuclear Recoil Scintillation Signals in Liquid Argon Laura Stonehill A novel approach to detection of low-energy astrophysical particles, such as the hypothesized WIMP dark matter, relies on measurement of scintillation light in noble liquids such as argon and neon. It is necessary to understand the differing response of such a detector to nuclear and electron recoil events. In order to measure this quenching of nuclear recoil signals, a D-D neutron generator was used to produce neutrons that scattered from a liquid argon cell into another detector at a series of known angles, so that the energies of the nuclear recoils in the liquid argon were kinematically determined. After calibrating the liquid argon detector with electron recoil events, the quenching factor for nuclear recoils was determined from the ratio of the measured electron-equivalent recoil energy at a given scattering angle to the expected nuclear recoil energy at that angle. Details of this measurement in the 4-kg liquid argon microCLEAN detector will be presented, along with quenching factor results for nuclear recoil energies of tens to hundreds of keV. [Preview Abstract] |
Saturday, April 14, 2007 3:42PM - 3:54PM |
E14.00002: A DEAP \& CLEAN Program for WIMP Dark Matter Andrew Hime Weakly Interacting Massive Particles (WIMPs) provide a compelling explanation for dark matter that could be directly detected as they recoil in massive and ultra-pure detector targets operating deep underground. Thus far, the direct detection of WIMPs has eluded the most sensitive of experiments and it is desirable to achieve sensitivities some three orders of magnitude beyond the state-of-the-art. This will require development of novel detector technologies exploiting target masses of order a ton and with unprecedented control of radioactive background in order to achieve the desired sensitivity of a single event per ton per year. We have realized a conceptually simple and scalable detector technology using the unique properties of scintillation light in liquid argon and liquid neon. Ultimately, we envision a very massive detector of liquid neon that could serve simultaneously as a detector of WIMP dark matter and low-energy (pp-fusion) solar neutrinos. A DEAP \& CLEAN program will be described that makes effective use of liquid argon and liquid neon, interchangeably, in a single detector. [Preview Abstract] |
Saturday, April 14, 2007 3:54PM - 4:06PM |
E14.00003: Optimization of Background Rejection in XENON10 Luiz de Viveiros The XENON10 Dark Matter Experiment, deployed at Gran Sasso Labs in Italy on March 2006, has been operating in dark matter search mode and (as of Dec 2006) has collected over 2 live months of data. The detector uses dual-phase (gas/liquid) xenon target of 15kg to search for nuclear recoils associated with WIMP events. The detector is able discriminate electron recoil and nuclear recoil events by means of the ratio of primary (prompt) scintillation to secondary scintillation from electro-luminescence caused by ionization electrons extracted into the gas phase. Better than 99{\%} discrimination of gamma background (at 50{\%} acceptance for nuclear recoil events) has been demonstrated in the initial running, with a gamma background of $<$1 event/kg/keV/day. The detector has threshold $<$10keV for nuclear recoil energy, and is sensitive to single electrons extracted from the liquid xenon. We will discuss parameters and methods used to optimize the rejection of electron recoil events which would otherwise look like nuclear recoil events. One such technique uses the primary scintillation hit pattern to identify electron recoil events that (as a result of field geometry in detector) have reduced charge collection, which therefore lowers the measured s2/s1 ratio. We will report on the results of the first 2 months of live operation and the estimated WIMP sensitivity achieved, and the factors affecting the overall dark matter sensitivity of the detector. [Preview Abstract] |
Saturday, April 14, 2007 4:06PM - 4:18PM |
E14.00004: Gamma background in the XENON-10 detector Jesse Angle The XENON-10 detector is the research and development phase leading up to a larger detector, using liquid xenon to directly search for dark matter (it is assumed that dark matter is composed of Weakly Interacting Massive Particles, or WIMP's).~ Due to the sensitivity needed for such a detector, it is vital to have a strong understanding of the background events that will be seen.~ Initial screening of many of the components comprising the XENON-10 detector has been completed using a High Purity Germanium detector.~ Results from said screening will be presented and the impact these results have on Monte Carlo simulations of the XENON-10 detector will be shown. [Preview Abstract] |
Saturday, April 14, 2007 4:18PM - 4:30PM |
E14.00005: Liquid neon as a scintillator for low energy particle detection James Nikkel Neon is a promising target material for use in WIMP dark matter detection as well as for low energy solar neutrino detection. In this presentation I will describe measurements of liquid neon scintillation due to both electronic and nuclear recoils. I will discuss properties such as signal yield, nuclear recoil scintillation efficiency and pulse shape discrimination. I will also address several technical challenges associated with using liquid neon in a particle detector. [Preview Abstract] |
Saturday, April 14, 2007 4:30PM - 4:42PM |
E14.00006: Physics of background discrimination in liquid xenon-based dark matter detectors Carl Dahl Dual-phase xenon detectors, as used for direct detection of WIMPs, discriminate between nuclear and electron recoils based on a ratio of ionization and scintillation signals. The underlying physics is the recombination of ions at the event site, which translates some fraction of the ionization signal into scintillation. We find the recombination-independent sum of the two signals and construct from this an energy scale with advantages in linearity and resolution over scales based on ionization or scintillation alone. From the improvement in resolution, we infer the magnitude of recombination fluctuations in electron and nuclear recoil tracks down to WIMP recoil energies. These fluctuations determine the fundamental discrimination capability of liquid xenon-based detectors. This work uses data from the Xenon collaboration prototype at Case Western and from the Xenon10 detector at Gran Sasso. [Preview Abstract] |
Saturday, April 14, 2007 4:42PM - 4:54PM |
E14.00007: Pulse Shape Discrimination (PSD) in Liquid Argon from DEAP-1 Bei Cai, Mark Boulay, Fraser Duncan, Kevin Graham, Aksel Hallin, Philip Harvey, Charles Hearns, Chris Jillings, Jeff Lidgard, Reuble Matthew, Paradorn Pasuthip, Peter Skensved DEAP (Dark Matter Experiment using Argon Pulse-shape discrimination) plans to search for WIMPs (Weakly Interacting Massive Particles) through elastic scattering on ${}^{40}$Ar. In this single-phase liquid argon (LAr) experiment discrimination of $\beta$ and $\gamma$ backgrounds from the WIMP-induced nuclear recoil signal is achieved by analyzing the pulse shape of scintillation light. The available pulse-shape discrimination (PSD) power at low energy (approx. 60 keV nuclear recoil) is examined using calibration data from DEAP-1, a 7 kg low-background LAr scintillation detector constructed at Queen's University in Canada, and compared to the required PSD for the planned 1000 kg LAr dark matter search. [Preview Abstract] |
Saturday, April 14, 2007 4:54PM - 5:06PM |
E14.00008: The Next Generation ZIP Detector for the Cryogenic Dark Matter Search Matt Pyle The `ZIP' detector (for z-position, ionization, and phonons) is used in the Cryogenic Dark Matter Search (CDMS) to detect nuclei recoiling from WIMP interactions and to discriminate nuclear recoils from various backgrounds. The experiment planned to succeed CDMS, known as SuperCDMS, proposes to improve upon the final CDMS sensitivity by at least an order of magnitude. To achieve this improvement, the design for the ZIP detector must be upgraded. In this talk we introduce the next generation of the ZIP detector with decreased surface to volume ratio, hydrogen passivated electrodes, and increased phonon sensor coverage due to novel Al fin geometry changes and discuss how these improvements will enable us to meet the proposed SuperCDMS sensitivity. This talk will be the last in a sequence of four from CDMS. [Preview Abstract] |
Saturday, April 14, 2007 5:06PM - 5:18PM |
E14.00009: Pulse shape discrimination in liquid argon W. Hugh Lippincott I present results from microCLEAN, a 4 kg liquid argon cell built as part of the CLEAN and DEAP programmes to detect dark matter in the form of WIMPs using scintillation light. The sensitivity of these detectors to dark matter is limited by the level of discrimination between electronic and nuclear recoils. Scintillation light is produced in the decay of metastable molecules that can exist in either the singlet or triplet state. Because the singlet state decays within a few nanoseconds while the triplet state has a lifetime of 1.6 microseconds, these components can be easily separated using timing information. Since electronic and nuclear recoils produce different ratios of singlet to triplet molecules, the relative size of the two components can determine what type of event occurred. I present two different discrimination algorithms, Prompt Fraction and Maximum Likelihood, and predict the discrimination power of larger detectors using these methods. [Preview Abstract] |
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