Bulletin of the American Physical Society
APS April Meeting 2012
Volume 57, Number 3
Saturday–Tuesday, March 31–April 3 2012; Atlanta, Georgia
Session W9: Direct Dark Matter Detection |
Hide Abstracts |
Sponsoring Units: DPF DAP Chair: Corbin Covault, Case Western Reserve University Room: Embassy E |
Tuesday, April 3, 2012 10:45AM - 10:57AM |
W9.00001: Measuring Neutron Response using Data and Monte Carlo Simulation in Xenon100 Paul Scovell A relative scintillation yield (L$_{eff}$) above 5.5 keV$_{r}$ (nuclear recoil energy) is determined using data from an exposure of XENON100 to neutrons from an Americium-Beryilium (AmBe) source. The technique requires a signal in the XENON100 Time Projection Chamber (TPC) to be in coincidence with a signal in the active liquid xenon (LXe) veto such that efficiency to low energy nuclear recoils is not compromised by the requirement of a signal in 2 or more photomultiplier tubes (PMTs). The L$_{eff}$ is then deduced (independently of any Monte Carlo simulation) through the comparison of the scintillation and ionization signals recorded. The calculated L$_{eff}$ is in excellent agreement with recent direct and indirect measurements. Comparison of the detector response to AmBe neutrons with an equivalent Monte Carlo generated spectrum is also performed. With the measured detector efficiency and a global fit to all measured values of L$_{eff}$, agreement between data and Monte Carlo down to a low photoelectron level is obtained. [Preview Abstract] |
Tuesday, April 3, 2012 10:57AM - 11:09AM |
W9.00002: Data analysis on XENON100 detector searching for WIMP Alfio Rizzo The XENON100 detector is a dual-phase xenon time projection chamber (LXeTPC) installed underground at the Laboratori Nazionali del Gran Sasso (Italy) and used to search for dark matter in the form of weakly interacting massive particles (WIMPs) by simultaneously measuring the scintillation and ionization signals produced by nuclear recoils. The 62 kg LXeTPC is instrumented by 178 PMTs and surrounded by a 99 kg Lxe active veto with 64 PMTs. XENON100 has set the most stringent limits on WIMP-nucleon interaction cross section to date, above 7E-45cm$^2$ at 90{\%} C.L., and continues to accrue blinded data towards a first robust discovery. We present the analysis techniques developed for the experiment and detail data selection procedures, quality cuts and efficiencies, as well the unblinding procedures for the experiment. Finally the methods for establishing presence of signal or for establishing a limit on interaction cross-section for WIMPs with matter are described. [Preview Abstract] |
Tuesday, April 3, 2012 11:09AM - 11:21AM |
W9.00003: The XENON1T Demonstrator Ran Budnik, Elena Aprile, Bin Choi, Hugo Contreras, Luke Goetzke, Kyungeun Lim, Rafael Lang, Antonio Melgarejo, Rino Persiani, Guillaume Plante, Alfio Rizzo, Peter Shagin We present the results from a facility called the XENON1T Demonstrator at Columbia University, that has been designed and built as a prototype for the XENON1T cryogenic system and TPC. Its primary goal is to demonstrate that the high LXe purity ($<1$ part per billion $O_2$ equivalent) required for electrons to drift freely over a distance of 1 meter, as in the XENON1T TPC, can be achieved and on a time scale of weeks. The approach adopted in all XENON detectors thus far is that of gas purification with continuous circulation with a diaphragm pump through a heated getter. We show results for high speed recirculation, above 100 slpm, the development of a high voltage feedthrough which is radio pure and the design and application of a prototype TPC to test the purity. [Preview Abstract] |
Tuesday, April 3, 2012 11:21AM - 11:33AM |
W9.00004: ABSTRACT WITHDRAWN |
Tuesday, April 3, 2012 11:33AM - 11:45AM |
W9.00005: Background estimation of the XENON1T Dark Matter Search Experiment Paolo Beltrame We will present the background estimation of the XENON1T detector, the next generation of the XENON phased Dark Matter search program. Detailed studies of both the electronic recoil and nuclear recoil background have been performed, including irreducible contamination from $pp$ chain solar neutrinos and 2$\nu\beta\beta$-decay of $^{136}$Xe.\\ By exploiting the excellent self-shielding and 3D position resolution of a LXeTPC, by selecting existing low radioactivity detector materials and by placing the detector in a large active water shield and Cherenkov muon veto, the overall event rate within the fiducial target of 1.1~ton is estimated to be less than 0.5~$\times~10^{-4}$ events/kg/day/keV$_{ee}$. This rate translates to less than one event per ton per year in the WIMP search region -- an unprecedented low background level for a dark matter experiment. For a $\sigma_{SI} \sim 10^{-45}$ cm$^2$ and $100$ GeV/c$^2$ WIMP mass, XENON1T would detect of order 100 events in this exposure, providing statistics for placing significant constraints on the WIMP mass. In the absence of signal XENON1T would be capable of probing WIMP interaction cross-sections to $\sigma_{SI}\sim 2\times10^{-47}$cm$^2$ within 2 years of operation. [Preview Abstract] |
Tuesday, April 3, 2012 11:45AM - 11:57AM |
W9.00006: New Measurement of $^{39}$Ar in Underground Argon with a Low Background Liquid Argon Detector Jingke Xu A low background liquid argon detector has been developed for sensitive measurements of the beta radioactive $^{39}$Ar in argon from underground sources. The measurement is motivated by the need to improve on earlier studies that showed no sign of $^{39}$Ar in certain sources of underground argon, but with a limited sensitivity of $\sim$ 5{\%} relative to $^{39}$Ar in atmospheric argon[1]. We will report preliminary measurements taken with the low background detector that was commissioned and operated at the Kimballton Underground Research Facility (KURF) in Virginia. A combination of passive and active background reduction techniques resulted in a very low background and a null result with sensitivity to~$^{39}$Ar less than 1{\%} of atmospheric. The results confirm that underground argon is well suited for direct detection of dark matter WIMPs. \\[4pt] [1] D. Acosta-Kane et al., Nucl. Instr. Meth. A \textbf{587}:46 (2008) [Preview Abstract] |
Tuesday, April 3, 2012 11:57AM - 12:09PM |
W9.00007: Status of the MiniCLEAN Dark Matter Experiment and $^{39}$Ar Background Simulation Thomas Caldwell The MiniCLEAN dark matter experiment, part of the DEAP/CLEAN program, is an ultra-low background single phase liquid argon and neon detector with a fiducial mass of 150 kg. The ability to exchange targets and the background rejection offered by noble liquids give MiniCLEAN a competitive sensitivity to WIMP dark matter, and these same features along with the scalability of the single phase approach allow MiniCLEAN to demonstrate the technologies required for the construction and operation of next generation multi-ton dark matter and precision low-energy solar neutrino experiments. I will discuss the status of the MiniCLEAN detector and some recent improvements to background rejection and the detector design based on $^{39}$Ar background studies using MiniCLEAN's simulation and analysis package. In particular, I will highlight detailed $^{39}$Ar background studies that have assisted in the development of improved particle identification which utilizes Bayesian single photoelectron counting and the particle dependence of the scintillation time profile. [Preview Abstract] |
Tuesday, April 3, 2012 12:09PM - 12:21PM |
W9.00008: In Situ Optical Calibration of MiniCLEAN Jui-Jen Wang, Franco Giuliani, Michael Gold The MiniCLEAN dark matter experiment will exploit a single-phase liquid-argon detector instrumented with 92 photomultiplier tubes placed in the cryogen temperature with 4-$\pi$ coverage of a 500 kg (150 kg) target (fiducial) mass. The detector design strategy emphasizes scalability to target masses of order 10 tons or more. The detector is designed also for a liquid-neon target that allows for an independent verification of signal and background and a test of the expected dependence of the WIMP-nucleus interaction rate. Being MiniCLEAN, as for the scintillation detector the PMT stability and calibration are essential. The optical calibration will be able monitor the system stability and keep the PMT in check. In MiniCLEAN, we use a Light-Emitting Diode(LED)-based light injection system to calibrate the PMTs. LEDs exhibit minimal pulse to pulse fluctuations in intensity, so the response of the PMT is dominated by photoelectron statistic. Also, the light intensity can be changed by software and high repetition rates are possible, so the calibration can be carried out quickly, which gives advantage on performing the calibration. [Preview Abstract] |
Tuesday, April 3, 2012 12:21PM - 12:33PM |
W9.00009: Measurement of the scintillation reponse of liquid xenon to electronic recoils down to low energies Kyungeun E. Lim, E. Aprile, R. Budnik, B. Choi, H.A. Contreras, K.-L. Giboni, L.W. Goetzke, J. Koglin, R.F. Lang, A.J. Melgarejo Fernandez, R. Persiani, G. Plante, A. Rizzo Understanding the electronic recoil response in liquid xenon (LXe) is important for the interpretation of results from dark matter experiments using LXe such as XENON100 and to estimate the electronic background contributions. As the first step, the energy dependence of the scintillation response at zero field was measured with a dedicated LXe detector. The scintillation response of LXe has been measured in the past at different energies using mono-energetic $\gamma$ sources. However, the Compton coincidence technique has the added benefit that the response can be measured at a continuum of energies. In this work, Compton scattered $\gamma$ rays were used to measure the scintillation light yield from electronic recoils below 100 keV. The high scintillation light collection of the detector enabled the lowest recoil energies to be probed to date. A comparison with the decays of Kr-83m is also presented. [Preview Abstract] |
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