Browsing by Author "Lindote, A."
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- 3D Modeling of Electric Fields in the LUX DetectorPublication . LUX collaboration (93 authors); Brás, P.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.This work details the development of a three-dimensional (3D) electric field model for the LUX detector. The detector took data to search for weakly interacting massive particles (WIMPs) during two periods. After the first period completed, a time-varying non-uniform negative charge developed in the polytetrafluoroethylene (PTFE) panels that define the radial boundary of the detector's active volume. This caused electric field variations in the detector in time, depth and azimuth, generating an electrostatic radially-inward force on electrons on their way upward to the liquid surface. To map this behavior, 3D electric field maps of the detector's active volume were generated on a monthly basis. This was done by fitting a model built in COMSOL Multiphysics to the uniformly distributed calibration data that were collected on a regular basis. The modeled average PTFE charge density increased over the course of the exposure from -3.6 to −5.5 μC/m2. From our studies, we deduce that the electric field magnitude varied locally while the mean value of the field of ~200 V/cm remained constant throughout the exposure. As a result of this work the varying electric fields and their impact on event reconstruction and discrimination were successfully modeled.
- $^{83\textrm{m}}$Kr calibration of the 2013 LUX dark matter searchPublication . LUX collaboration (93 authors); Brás, P.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.LUX was the first dark matter experiment to use a Kr83m calibration source. In this paper, we describe the source preparation and injection. We also present several Kr83m calibration applications in the context of the 2013 LUX exposure, including the measurement of temporal and spatial variation in scintillation and charge signal amplitudes, and several methods to understand the electric field within the time projection chamber.
- 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.
- Calibration, event reconstruction, data analysis, and limit calculation for the LUX dark matter experimentPublication . LUX collaboration (98 authors); Brás, P.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.The LUX experiment has performed searches for dark matter particles scattering elastically on xenon nuclei, leading to stringent upper limits on the nuclear scattering cross sections for dark matter. Here, for results derived from ${1.4}\times 10^{4}\;\mathrm{kg\,days}$ of target exposure in 2013, details of the calibration, event-reconstruction, modeling, and statistical tests that underlie the results are presented. Detector performance is characterized, including measured efficiencies, stability of response, position resolution, and discrimination between electron- and nuclear-recoil populations. Models are developed for the drift field, optical properties, background populations, the electron- and nuclear-recoil responses, and the absolute rate of low-energy background events. Innovations in the analysis include in situ measurement of the photomultipliers' response to xenon scintillation photons, verification of fiducial mass with a low-energy internal calibration source, and new empirical models for low-energy signal yield based on large-sample, in situ calibrations.
- 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.
- First Searches for Axions and Axionlike Particles with the LUX ExperimentPublication . LUX collaboration (101 authors); Brás, P.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.The first searches for axions and axionlike particles with the Large Underground Xenon experiment are presented. Under the assumption of an axioelectric interaction in xenon, the coupling constant between axions and electrons gAe is tested using data collected in 2013 with an exposure totaling 95 live days ×118 kg. A double-sided, profile likelihood ratio statistic test excludes gAe larger than 3.5×10-12 (90% C.L.) for solar axions. Assuming the Dine-Fischler-Srednicki-Zhitnitsky theoretical description, the upper limit in coupling corresponds to an upper limit on axion mass of 0.12 eV/c2, while for the Kim-Shifman-Vainshtein-Zhakharov description masses above 36.6 eV/c2 are excluded. For galactic axionlike particles, values of gAe larger than 4.2×10-13 are excluded for particle masses in the range 1–16 keV/c2. These are the most stringent constraints to date for these interactions.
- 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.
- Identification of Radiopure Titanium for the LZ Dark Matter Experiment and Future Rare Event SearchesPublication . LZ collaboration (205 authors); Brás, P.; Lindote, A.; Lopes, M.I.; Neves, F.; Silva, C.; Solovov, V.N.The LUX-ZEPLIN (LZ) experiment will search for dark matter particle interactions with a detector containing a total of 10 tonnes of liquid xenon within a double-vessel cryostat. The large mass and proximity of the cryostat to the active detector volume demand the use of material with extremely low intrinsic radioactivity. We report on the radioassay campaign conducted to identify suitable metals, the determination of factors limiting radiopure production, and the selection of titanium for construction of the LZ cryostat and other detector components. This titanium has been measured with activities of $^{238}$U$_{e}$~$<$1.6~mBq/kg, $^{238}$U$_{l}$~$<$0.09~mBq/kg, $^{232}$Th$_{e}$~$=0.28\pm 0.03$~mBq/kg, $^{232}$Th$_{l}$~$=0.25\pm 0.02$~mBq/kg, $^{40}$K~$<$0.54~mBq/kg, and $^{60}$Co~$<$0.02~mBq/kg (68\% CL). Such low intrinsic activities, which are some of the lowest ever reported for titanium, enable its use for future dark matter and other rare event searches. Monte Carlo simulations have been performed to assess the expected background contribution from the LZ cryostat with this radioactivity. In 1,000 days of WIMP search exposure of a 5.6-tonne fiducial mass, the cryostat will contribute only a mean background of $0.160\pm0.001$(stat)$\pm0.030$(sys) counts.
- 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.