C. Silva

First limits on WIMP nuclear recoil signals in ZEPLIN-II: A two-phase xenon detector for dark matter detection

Abstract Results are presented from the first underground data run of ZEPLIN-II, a 31xa0kg two-phase xenon detector developed to observe nuclear recoils from hypothetical weakly interacting massive dark matter particles. Discrimination between nuclear recoils and background electron recoils is afforded by recording both the scintillation and ionisation signals generated within the liquid xenon, with the ratio of these signals being different for the two classes of event. This ratio is calibrated for different incident species using an AmBe neutron source and 60 Co γ-ray sources. From our first 31 live days of running ZEPLIN-II, the total exposure following the application of fiducial and stability cuts was 225xa0kgxa0×xa0days. A background population of radon progeny events was observed in this run, arising from radon emission in the gas purification getters, due to radon daughter ion decays on the surfaces of the walls of the chamber. An acceptance window, defined by the neutron calibration data, of 50% nuclear recoil acceptance between 5xa0keV ee and 20xa0keV ee , had an observed count of 29 events, with a summed expectation of 28.6xa0±xa04.3 γ-ray and radon progeny induced background events. These figures provide a 90% c.l. upper limit to the number of nuclear recoils of 10.4 events in this acceptance window, which converts to a WIMP–nucleon spin-independent cross-section with a minimum of 6.6xa0×xa010 −7 xa0pb following the inclusion of an energy-dependent, calibrated, efficiency. A second run is currently underway in which the radon progeny will be eliminated, thereby removing the background population, with a projected sensitivity of 2xa0×xa010 −7 xa0pb for similar exposures as the first run.

The ZEPLIN-III dark matter detector: Instrument design, manufacture and commissioning

We present details of the technical design, manufacture and testing of the ZEPLIN-III dark matter experiment. ZEPLIN-III is a two-phase xenon detector which measures both the scintillation light and the ionisation charge generated in the liquid by interacting particles and radiation. The instrument design is driven by both the physics requirements and by the technology requirements surrounding the use of liquid xenon. These include considerations of key performance parameters, such as the efficiency of scintillation light collection, restrictions placed on the use of materials to control the inherent radioactivity levels, attainment of high vacuum levels and chemical contamination control. The successful solution has involved a number of novel design and manufacturing features which will be of specific use to future generations of direct dark matter search experiments as they struggle with similar and progressively more demanding requirements.

Limits on spin-dependent WIMP-nucleon cross section obtained from the complete LUX exposure

We present experimental constraints on the spin-dependent WIMP-nucleon elastic cross sections from the total 129.5u2009u2009kgu2009yr exposure acquired by the Large Underground Xenon experiment (LUX), operating at the Sanford Underground Research Facility in Lead, South Dakota (USA). A profile likelihood ratio analysis allows 90%xa0C.L. upper limits to be set on the WIMP-neutron (WIMP-proton) cross section of σ_{n}=1.6×10^{-41}u2009u2009cm^{2} (σ_{p}=5×10^{-40}u2009u2009cm^{2}) at 35u2009u2009GeVu2009c^{-2}, almost a sixfold improvement over the previous LUX spin-dependent results. The spin-dependent WIMP-neutron limit is the most sensitive constraint to date.

The ZEPLIN-III dark matter detector: Performance study using an end-to-end simulation tool

We present results from a GEANT4-based Monte Carlo tool for end-to-end simulations of the ZEPLIN-III dark matter experiment. ZEPLIN-III is a two-phase detector which measures both the scintillation light and the ionisation charge generated in liquid xenon by interacting particles and radiation. The software models the instrument response to radioactive backgrounds and calibration sources, including the generation, ray-tracing and detection of the primary and secondary scintillations in liquid and gaseous xenon, and subsequent processing by data acquisition electronics. A flexible user interface allows easy modification of detector parameters at run time. Realistic datasets can be produced to help with data analysis, an example of which is the position reconstruction algorithm developed from simulated data. We present a range of simulation results confirming the original design sensitivity of a few times 10−8 pb to the WIMP-nucleon cross-section.

Limits on spin-dependent WIMP-nucleon cross-sections from the first ZEPLIN-II data

The first underground data run of the ZEPLIN-II experiment has set a limit on the nuclear recoil rate in the two-phase xenon detector for direct dark matter searches. In this Letter the results from this run are converted into the limits on spin-dependent WIMP-proton and WIMP-neutron cross-sections. The minimum of the curve for WIMP-neutron cross-section corresponds to 7 × 10−2 pb at a WIMP mass of around 65 GeV.

Ultralow energy calibration of LUX detector using Xe127 electron capture

Author(s): Akerib, DS; Alsum, S; Araujo, HM; Bai, X; Bailey, AJ; Balajthy, J; Beltrame, P; Bernard, EP; Bernstein, A; Biesiadzinski, TP; Boulton, EM; Bras, P; Byram, D; Cahn, SB; Carmona-Benitez, MC; Chan, C; Currie, A; Cutter, JE; Davison, TJR; Dobi, A; Druszkiewicz, E; Edwards, BN; Fallon, SR; Fan, A; Fiorucci, S; Gaitskell, RJ; Genovesi, J; Ghag, C; Gilchriese, MGD; Hall, CR; Hanhardt, M; Haselschwardt, SJ; Hertel, SA; Hogan, DP; Horn, M; Huang, DQ; Ignarra, CM; Jacobsen, RG; Ji, W; Kamdin, K; Kazkaz, K; Khaitan, D; Knoche, R; Larsen, NA; Lenardo, BG; Lesko, KT; Lindote, A; Lopes, MI; Manalaysay, A; Mannino, RL; Marzioni, MF; McKinsey, DN; Mei, DM; Mock, J; Moongweluwan, M; Morad, JA; Murphy, ASJ; Nehrkorn, C; Nelson, HN; Neves, F; OSullivan, K; Oliver-Mallory, KC; Palladino, KJ; Pease, EK; Rhyne, C; Shaw, S; Shutt, TA; Silva, C; Solmaz, M; Solovov, VN; Sorensen, P; Sumner, TJ; Szydagis, M; Taylor, DJ; Taylor, WC; Tennyson, BP; Terman, PA; Tiedt, DR; To, WH; Tripathi, M; Tvrznikova, L; Uvarov, S; Velan, V; Verbus, JR; Webb, RC | Abstract:

Position reconstruction in LUX

Author(s): Akerib, DS; Alsum, S; Arauandjo, HM; Bai, X; Bailey, AJ; Balajthy, J; Beltrame, P; Bernard, EP; Bernstein, A; Biesiadzinski, TP; Boulton, EM; Braands, P; Byram, D; Cahn, SB; Carmona-Benitez, MC; Chan, C; Currie, A; Cutter, JE; Davison, TJR; Dobi, A; Druszkiewicz, E; Edwards, BN; Fallon, SR; Fan, A; Fiorucci, S; Gaitskell, RJ; Genovesi, J; Ghag, C; Gilchriese, MGD; Hall, CR; Hanhardt, M; Haselschwardt, SJ; Hertel, SA; Hogan, DP; Horn, M; Huang, DQ; Ignarra, CM; Jacobsen, RG; Ji, W; Kamdin, K; Kazkaz, K; Khaitan, D; Knoche, R; Larsen, NA; Lenardo, BG; Lesko, KT; Lindote, A; Lopes, MI; Manalaysay, A; Mannino, RL; Marzioni, MF; McKinsey, DN; Mei, DM; Mock, J; Moongweluwan, M; Morad, JA; Murphy, ASJ; Nehrkorn, C; Nelson, HN; Neves, F; OSullivan, K; Oliver-Mallory, KC; Palladino, KJ; Pease, EK; Rhyne, C; Shaw, S; Shutt, TA; Silva, C; Solmaz, M; Solovov, VN; Sorensen, P; Sumner, TJ; Szydagis, M; Taylor, DJ; Taylor, WC; Tennyson, BP; Terman, PA; Tiedt, DR; To, WH; Tripathi, M; Tvrznikova, L; Uvarov, S; Velan, V; Verbus, JR; Webb, RC | Abstract:

3D modeling of electric fields in the LUX detector

Author(s): Akerib, DS; Alsum, S; Araujo, HM; Bai, X; Bailey, AJ; Balajthy, J; Beltrame, P; Bernard, EP; Bernstein, A; Biesiadzinski, TP; Boulton, EM; Bras, P; Byram, D; Cahn, SB; Carmona-Benitez, MC; Chan, C; Currie, A; Cutter, JE; Davison, TJR; Dobi, A; Druszkiewicz, E; Edwards, BN; Fallon, SR; Fan, A; Fiorucci, S; Gaitskell, RJ; Genovesi, J; Ghag, C; Gilchriese, MGD; Hall, CR; Hanhardt, M; Haselschwardt, SJ; Hertel, SA; Hogan, DP; Horn, M; Huang, DQ; Ignarra, CM; Jacobsen, RG; Ji, W; Kamdin, K; Kazkaz, K; Khaitan, D; Knoche, R; Larsen, NA; Lenardo, BG; Lesko, KT; Lindote, A; Lopes, MI; Manalaysay, A; Mannino, RL; Marzioni, MF; McKinsey, DN; Mei, DM; Mock, J; Moongweluwan, M; Morad, JA; Murphy, ASJ; Nehrkorn, C; Nelson, HN; Neves, F; OSullivan, K; Oliver-Mallory, KC; Palladino, KJ; Pease, EK; Rhyne, C; Shaw, S; Shutt, TA; Silva, C; Solmaz, M; Solovov, VN; Sorensen, P; Sumner, TJ; Szydagis, M; Taylor, DJ; Taylor, WC; Tennyson, BP; Terman, PA; Tiedt, DR; To, WH; Tripathi, M; Tvrznikova, L; Uvarov, S; Velan, V; Verbus, JR; Webb, RC | Abstract: