Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session B13: Dark Matter I |
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Sponsoring Units: DPF Chair: Daniel Akerib, Case Western Reserve University Room: Hyatt Regency Jacksonville Riverfront City Terrace 9 |
Saturday, April 14, 2007 10:45AM - 11:09AM |
B13.00001: First Results from the XENON10 Dark Matter Experiment the Gran Sasso Underground Lab Elena Aprile We report the first results from a search for Weakly Interacting Massive Particles (WIMPs) with the XENON10 experiment operating underground at the Gran Sasso Laboratory. XENON10 is the first dual phase xenon time projection chamber (XeTPC) module realized within the XENON program. The 3D-postion sensitive detector has an active mass of 15 kg of liquid xenon, viewed by two arrays of compact photomultipliers, to measure simultaneously the scintillation and the ionization, via proportional scintillation in the gas. Background rejection on an event-by-event basis is achieved through this measurement and 3D event localization. The detector was deployed underground in Spring 2006 and mounted in its shield in Summer 2006. The experiment has been operating continuously for the past five months, with a high degree of stability and very good performance. The energy threshold is $<$10 keV and the background rate is $<$1evt/kg/keV/day. In-situ gamma and neutron calibrations have been carried out to define event selection and energy threshold for nuclear recoil candidates. Data taking continues as of this writing. A blind analysis on the latest months of data is currently being performed using only calibration data. WIMP search results are expected by early Spring 2007. [Preview Abstract] |
Saturday, April 14, 2007 11:09AM - 11:21AM |
B13.00002: Characterization of the Light Response of the XENON-10 Dark Matter Detector Roman Gomez The dual-phase liquid/gas xenon time projection chamber for the search of Dark Matter, XENON-10, relies on the detection of charge and light within the sensitive detector. We describe simulations of the scintillation light response of XENON-10 in the light-sensitive volume and compare these results to calibration data. The PMT pattern of scintillation light provides a strong consistency check with the X/Y-position derived from the charge signal (detected via proportional scintillation in the gas phase) given the Z-coordinate measured by the electron drift time. In the current detector, the light-sensitive volume is greater than the charge-sensitive volume, which implies regions of partial information, not usable for Dark Matter detection, but potentially relevant for the understanding of backgrounds in the fully sensitive detector volume. [Preview Abstract] |
Saturday, April 14, 2007 11:21AM - 11:33AM |
B13.00003: Nuclear recoil discrimination in the Xenon10 detector. Aaron Manalaysay The Xenon10 detector searches for Cold Dark Matter in the form of Weakly Interacting Massive Particles (WIMPs) using a dual-phase liquid xenon time projection chamber, which simultaneously measures energy deposition in the form of scintillation (S1) and ionization (S2). The single most important feature of this detector is its ability to perform nuclear recoil discrimination, allowing one to veto gamma rays due to background sources. The differing track structures of electronic recoils (gammas, betas, etc.) and nuclear recoils (WIMPs, neutrons) produce characteristically different ratios of S2 to S1 for a given recoil energy. I present the actual discrimination performance of this detector in the context of a direct WIMP search, based on in situ gamma and neutron calibrations. [Preview Abstract] |
Saturday, April 14, 2007 11:33AM - 11:45AM |
B13.00004: Response of XENON10 to Neutrons: Comparison of Monte Carlo and data. Angel Manzur The XENON experiment uses liquid xenon (LXe) as the target medium for detecting Cold Dark Matter in the form of Weakly Interacting Massive Particles (WIMPs). Event by event discrimination is achieved by simultaneously measuring the ionization and scintillation signal produced by nuclear recoil events. The discrimination power is calibrated based on neutron and gamma calibrations done using external AmBe and Cs-137 sources. A WIMP interacting in the LXe is expected to have a similar signature in the detector as the elastic scattering of a neutron with energy of a few MeV. The comparison of Monte Carlo simulations with neutron calibration data gives us a deeper understanding of the detector, calibrates nuclear recoil acceptance fraction for different background cuts, and helps to optimize the data cuts to achieve best WIMP sensitivity. Here we present a comparison between the Monte Carlo simulations done for Xenon10 with results from the neutron calibrations. [Preview Abstract] |
Saturday, April 14, 2007 11:45AM - 11:57AM |
B13.00005: The DEAP-1 Experiment at SNOLAB Chris Jillings DEAP-1 is a 7-kg liquid-argon dark matter detector which will be deployed in SNOLAB early in 2007. DEAP-1 uses pulse-shape discrimination to separate nuclear-recoil events from electromagnetic events and is part of a staged program to construct a one-tonne scale detector. With two live years we have a projected sensitivity to WIMP dark-matter of $10^{-44}\,\mbox{cm}^2$. DEAP-1 . SNOLAB has 6010 meters water equivalent flat overburden reducing muon rates to $0.27 \,\mbox{m}^{-2}\mbox{day}{^-1}$. The design and construction of the detector and control of backgrounds will be presented. [Preview Abstract] |
Saturday, April 14, 2007 11:57AM - 12:09PM |
B13.00006: Calibrating the Xenon10 Detector with Activated Xenon Kaixuan Ni Xenon10 is a 15-kg liquid xenon (LXe) detector for the search of dark matter in the form of weakly interacting massive particles (WIMPs). The high scintillation yield of LXe and high light collection efficiency in Xenon10 allow the detection of low-energy nuclear recoils, e.g. from WIMPs elastic scattering, down to 10 keV. The energy calibration is usually performed by using external gamma ray sources, such as Co-57 and Cs-137. However, external low-energy gamma rays are not very useful to calibrate the central part of the detector due to their small interaction length ($\sim $mm) in LXe. Calibrations from external high-energy gamma rays are also not accurate due to gamma-ray's non-uniform distributions in the target and non-linearity of LXe scintillation yield for different energies. Here we introduce a new calibration method by using neutron-activated xenon, which emits 164 keV and 236 keV gamma rays uniformly in the target and provides precise energy calibration in every part of the detector. The method also allows the study of position-dependence of the signals, further improving the detector's energy resolution and background rejection capability. [Preview Abstract] |
Saturday, April 14, 2007 12:09PM - 12:21PM |
B13.00007: 3D Event Position Reconstruction in the XENON10 Dark Matter Detector Roberto Santorelli XENON10 is a 15-kg dual phase xenon TPC (Time Projection Chamber) whose aim is to search for dark matter WIMPs (Weakly Interacting Massive Particles). The detector's 3D-position sensitivity enables a good reduction of the gamma-induced background rate, by rejecting events localized near the edges and the surfaces of the sensitive volume. A X-Y position reconstruction algorithm based on a Neural Network (NN) technique has been developed in order to improve event localization, especially near the edges of the sensitive volume. The performance of the NN algorithm has been tested and shown to be superior than that achieved with an algorithm based on a $\chi^2$ minimization of the differences between real events and a map of Monte Carlo (MC) simulated events. The results from gamma calibration data (Cs-137 source and background) and MC events show that the NN method provides better position resolution and a better edge events identification than the previous method. [Preview Abstract] |
Saturday, April 14, 2007 12:21PM - 12:33PM |
B13.00008: Calibration of the XENON10 detector Guillaume Plante The XENON10 detector is a 15 kg dual-phase liquid xenon time projection chamber used to search for dark matter weakly interacting massive particles (WIMPs) by simultaneously measuring the scintillation and ionization of nuclear recoils. The energy calibration of the detector (as well as its response to electron recoils) is performed using external gamma-ray sources (Cs-137 and Co-57) while its response to nuclear recoils is obtained using a neutron source (AmBe). We discuss how different detector performance parameters such as light yield and electron lifetime can be infered from these calibrations and show how the spatial dependence of some other parameters (light collection efficiency for example) can be obtained. We also present comparisons of results from calibrations with Monte Carlo simulations. [Preview Abstract] |
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