Browsing by Author "de Viveiros, L."
Now showing 1 - 10 of 14
Results Per Page
Sort Options
- An Ultra-Low Background PMT for Liquid Xenon DetectorsPublication . Akerib, D.S. et al. (64 authors); de Viveiros, L.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.Results are presented from radioactivity screening of two models of photomultiplier tubes designed for use in current and future liquid xenon experiments. The Hamamatsu 5.6cm diameter R8778 PMT, used in the LUX dark matter experiment, has yielded a positive detection of four common radioactive isotopes: ^2^3^8U, ^2^3^2Th, ^4^0K, and ^6^0Co. Screening of LUX materials has rendered backgrounds from other detector materials subdominant to the R8778 contribution. A prototype Hamamatsu 7.6cm diameter R11410 MOD PMT has also been screened, with benchmark isotope counts measured at <0.4^2^3^8U/<0.3^2^3^2Th/<8.3^4^0K/2.0+/-0.2 ^6^0Co mBq/PMT. This represents a large reduction, equal to a change of x124^2^3^8U/x19^2^3^2Th/x18^4^0K per PMT, between R8778 and R11410 MOD, concurrent with a doubling of the photocathode surface area (4.5-6.4cm diameter). ^6^0Co measurements are comparable between the PMTs, but can be significantly reduced in future R11410 MOD units through further material selection. Assuming PMT activity equal to the measured 90% upper limits, Monte Carlo estimates indicate that replacement of R8778 PMTs with R11410 MOD PMTs will change LUX PMT electron recoil background contributions by a factor of x125 after further material selection for ^6^0Co reduction, and nuclear recoil backgrounds by a factor of x136. The strong reduction in backgrounds below the measured R8778 levels makes the R11410 MOD a very competitive technology for use in large-scale liquid xenon detectors.
- First results from the LUX dark matter experiment at the Sanford Underground Research FacilityPublication . LUX collaboration (102 authors); de Viveiros, L.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.The Large Underground Xenon (LUX) experiment, a dual-phase xenon time-projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota), was cooled and filled in February 2013. We report results of the first WIMP search dataset, taken during the period April to August 2013, presenting the analysis of 85.3 live-days of data with a fiducial volume of 118 kg. A profile-likelihood analysis technique shows our data to be consistent with the background-only hypothesis, allowing 90% confidence limits to be set on spin-independent WIMP-nucleon elastic scattering with a minimum upper limit on the cross section of $7.6 \times 10^{-46}$ cm$^{2}$ at a WIMP mass of 33 GeV/c$^2$. We find that the LUX data are in strong disagreement with low-mass WIMP signal interpretations of the results from several recent direct detection experiments.
- First Results of the LUX Dark Matter ExperimentPublication . LUX collaboration (86 authors); de Viveiros, L.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.LUX (Large Underground Xenon) is a dark matter direct detection experiment deployed at the 4850' level of the Sanford Underground Research Facility (SURF) in Lead, SD, operating a 370 kg dual-phase xenon TPC. Results of the first WIMP search run were presented in late 2013, for the analysis of 85.3 live-days with a fiducial volume of 118 kg, taken during the period of April to August 2013. The experiment exhibited a sensitivity to spin-independent WIMP-nucleon elastic scattering with a minimum upper limit on the cross section of 7.6×10−46cm2 at a WIMP mass of 33 GeV/c 2 , becoming the world's leading WIMP search result, in conflict with several previous claimed hints of discovery.
- FPGA-based Trigger System for the LUX Dark Matter ExperimentPublication . LUX collaboration (102 authors); de Viveiros, L.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.LUX is a two-phase (liquid/gas) xenon time projection chamber designed to detect nuclear recoils resulting from interactions with dark matter particles. Signals from the detector are processed with an FPGA-based digital trigger system that analyzes the incoming data in real-time, with just a few microsecond latency. The system enables first pass selection of events of interest based on their pulse shape characteristics and 3D localization of the interactions. It has been shown to be >99% efficient in triggering on S2 signals induced by only few extracted liquid electrons. It is continuously and reliably operating since its full underground deployment in early 2013. This document is an overview of the systems capabilities, its inner workings, and its performance.
- Improved Limits on Scattering of Weakly Interacting Massive Particles from Reanalysis of 2013 LUX DataPublication . LUX collaboration (101 authors); de Viveiros, L.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.We present constraints on weakly interacting massive particles (WIMP)-nucleus scattering from the 2013 data of the Large Underground Xenon dark matter experiment, including 1.4×104 kg day of search exposure. This new analysis incorporates several advances: single-photon calibration at the scintillation wavelength, improved event-reconstruction algorithms, a revised background model including events originating on the detector walls in an enlarged fiducial volume, and new calibrations from decays of an injected tritium β source and from kinematically constrained nuclear recoils down to 1.1 keV. Sensitivity, especially to low-mass WIMPs, is enhanced compared to our previous results which modeled the signal only above a 3 keV minimum energy. Under standard dark matter halo assumptions and in the mass range above 4 GeV c-2, these new results give the most stringent direct limits on the spin-independent WIMP-nucleon cross section. The 90% C.L. upper limit has a minimum of 0.6 zb at 33 GeV c-2 WIMP mass.
- LUX Cryogenics and CirculationPublication . Bradley, A.W. et al. (67 authors); de Viveiros, L.; Lindote, A.; Lopes, M.I.; Neves, F.; Da Cunha, J. Pinto; Silva, C.; Solovov, V.N.We report the effciency of a thermosyphon-based cooling system for a liquid xenon (LXe) time projection chamber (TPC), as well as the effciency of a unique internal heat exchanger with standard gas phase purification using a heated getter, which allows for very high flow purification without requiring large cooling power.
- Proposed low-energy absolute calibration of nuclear recoils in a dual-phase noble element TPC using D-D neutron scattering kinematicsPublication . Verbus, J.R.; Rhyne, C.A.; Malling, D.C.; Genecov, M.; Ghosh, S.; Moskowitz, A.G.; Chan, S.; Chapman, J.J.; de Viveiros, L.; Faham, C.H.; Fiorucci, S.; Huang, D.Q.; Pangilinan, M.; Taylor, W.C.; Gaitskell, R.J.We propose a new technique for the calibration of nuclear recoils in large noble element dual-phase time projection chambers used to search for WIMP dark matter in the local galactic halo. This technique provides an $\textit{in situ}$ measurement of the low-energy nuclear recoil response of the target media using the measured scattering angle between multiple neutron interactions within the detector volume. The low-energy reach and reduced systematics of this calibration have particular significance for the low-mass WIMP sensitivity of several leading dark matter experiments. Multiple strategies for improving this calibration technique are discussed, including the creation of a new type of quasi-monoenergetic 272 keV neutron source. We report results from a time-of-flight based measurement of the neutron energy spectrum produced by an Adelphi Technology, Inc. DD108 neutron generator, confirming its suitability for the proposed nuclear recoil calibration.
- Radiogenic and Muon-Induced Backgrounds in the LUX Dark Matter DetectorPublication . Akerib, D.S. et al. (80 authors); de Viveiros, L.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.The Large Underground Xenon (LUX) dark matter experiment aims to detect rare low-energy interactions from Weakly Interacting Massive Particles (WIMPs). The radiogenic backgrounds in the LUX detector have been measured and compared with Monte Carlo simulation. Measurements of LUX high-energy data have provided direct constraints on all background sources contributing to the background model. The expected background rate from the background model for the 85.3 day WIMP search run is $(2.6\pm0.2_{\textrm{stat}}\pm0.4_{\textrm{sys}})\times10^{-3}$~events~keV$_{ee}^{-1}$~kg$^{-1}$~day$^{-1}$ in a 118~kg fiducial volume. The observed background rate is $(3.6\pm0.4_{\textrm{stat}})\times10^{-3}$~events~keV$_{ee}^{-1}$~kg$^{-1}$~day$^{-1}$, consistent with model projections. The expectation for the radiogenic background in a subsequent one-year run is presented.
- Radon-related Backgrounds in the LUX Dark Matter SearchPublication . Bradley, A. et al. (80 authors); de Viveiros, L.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.The LUX detector is currently in operation at the Davis Campus at the 4850’ level of the Sanford Underground Research Facility (SURF) in Lead, SD to directly search for WIMP dark matter. Knowing the type and rate of backgrounds is critical in a rare, low energy event search, and LUX was designed, constructed, and deployed to mitigate backgrounds, both internal and external. An important internal background are decays of radon and its daughters. These consist of alpha decays, which are easily tagged and are a tracer of certain backgrounds, and beta decays, some of which are not as readily tagged and present a background for the WIMP search. We report on studies of alpha decay and discuss implications for the WIMP search.
- Results on the Spin-Dependent Scattering of Weakly Interacting Massive Particles on Nucleons from the Run 3 Data of the LUX ExperimentPublication . LUX collaboration (101 authors); de Viveiros, L.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.We present experimental constraints on the spin-dependent WIMP (weakly interacting massive particle)-nucleon elastic cross sections from LUX data acquired in 2013. LUX is a dual-phase xenon time projection chamber operating at the Sanford Underground Research Facility (Lead, South Dakota), which is designed to observe the recoil signature of galactic WIMPs scattering from xenon nuclei. A profile likelihood ratio analysis of 1.4×104 kg day of fiducial exposure allows 90% C.L. upper limits to be set on the WIMP-neutron (WIMP-proton) cross section of σn=9.4×10-41 cm2 (σp=2.9×10-39 cm2) at 33 GeV/c2. The spin-dependent WIMP-neutron limit is the most sensitive constraint to date.