445 results found
Sumner TJ, 2010, ZEPLIN-III
ZEPLIN-III is a 12 kg two-phase xenon time projection chamber used to search for the weakly interacting massive particles (WIMPs) that may account for the dark matter of our Galaxy. The detector measures both scintillation and ionisation produced interactions in the liquid to differentiate between nuclear recoils expected from WIMPs and electron recoil background signals down to ∼10 keV nuclear recoil energy. This paper reviews the science results obtained from the frst science run and reports on the current status of the upgrade and second science run. The frst science run obtained 847kgdays of data acquired between February 27th 2008 and May 20th 2008 and excluded a WIMP-nucleon elastic scattering spin-independent cross-section above 8.1 × 10-8pb at 60 GeVc-2 with a 90% confdence limit. ZEPLIN-III demonstrated better discrimination at low-energy than previously achieved by any other xenon-based experiments and highlighted a non-linearity in the low-energy response to nuclear recoils. The upgrade includes replacement of the PMT array and the addition of an active veto for gammas and neutrons. The second science run should offer an order of magnitude improvement in sensitivity. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.
We present limits on the WIMP–nucleon cross section for inelastic dark matter from a reanalysis of the2008 run of ZEPLIN-III. Cuts, notably on scintillation pulse shape and scintillation-to-ionisation ratio, givea net exposure of 63 kg day in the range 20–80 keV nuclear recoil energy, in which 6 events are observed.Upper limits on signal rate are derived from the maximum empty patch in the data. Under standard haloassumptions a small region of parameter space consistent, at 99% CL, with causing the 1.17 ton yr DAMAmodulation signal is allowed at 90% CL: it is in the mass range 45–60 GeVc−2 with a minimum CLof 87%, again derived from the maximum patch. This is the tightest constraint yet presented using xenon,a target nucleus whose similarity to iodine mitigiates systematic error from the assumed halo.
The design, optimisation and construction of an anti-coincidence veto detector to complement the ZEPLIN-III direct dark matter search instrument is described. One tonne of plastic scintillator is arranged into 52 bars individually read out by photomultipliers and coupled to a gadolinium-loaded passive polypropylene shield. Particular attention has been paid to radiological content. The overall aim has been to achieve a veto detector of low threshold and high efficiency without the creation of additional background in ZEPLIN-III, all at a reasonable cost. Extensive experimental measurements of the components have been made, including radioactivity levels and performance characteristics. These have been used to inform a complete end-to-end Monte Carlo simulation that has then been used to calculate the expected performance of the new instrument, both operating alone and as an anti-coincidence detector for ZEPLIN-III. The veto device will be capable of rejecting over 65% of coincident nuclear recoil events from neutron background in the energy range of interest in ZEPLIN-III. This will reduce the background in ZEPLIN-III from ≃0.4 to ≃0.14 events per year in the WIMP acceptance region, a significant factor in the event of a non-zero observation. Furthermore, in addition to providing valuable diagnostic capabilities, the veto is capable of tagging over 15% for γ-ray rejection, all whilst contributing no significant additional background. In conjunction with the replacement of the internal ZEPLIN-III photomultiplier array, the new veto is expected to improve significantly the sensitivity of the ZEPLIN-III instrument to dark matter, allowing spin-independent WIMP-nucleon cross sections below 10−8 pb to be probed.
Grimani C, Araujo HM, Fabi M, et al., 2010, Short-term forecasting of solar energetic ions on board LISA, 8th Edoardo Amaldi Conference on Gravitational Waves, Publisher: IOP PUBLISHING LTD, ISSN: 1742-6588
Sumner TJ, 2009, The STEP and GAUGE Missions, Publisher: SPRINGER, Pages: 475-487, ISSN: 0038-6308
Khan SA, Chanial PF, Willner SP, et al., 2009, On the nature of the first galaxies selected at 350 μm, Astrophysical Journal, Vol: 706, Pages: 319-327, ISSN: 1538-4357
We present constraints on the nature of the first galaxies selected at 350 μm. The sample includes galaxies discovered in the deepest blank-field survey at 350 μm (in the Boötes Deep Field) and also later serendipitous detections in the Lockman Hole. In determining multiwavelength identifications, the 350 μm position and map resolution of the second generation Submillimeter High Angular Resolution Camera are critical, especially in the cases where multiple radio sources exist and the 24 μm counterparts are unresolved. Spectral energy distribution templates are fitted to identified counterparts, and the sample is found to comprise IR-luminous galaxies at 1 < z < 3 predominantly powered by star formation. The first spectrum of a 350 μm selected galaxy provides an additional confirmation, showing prominent dust grain features typically associated with star-forming galaxies. Compared to submillimeter galaxies selected at 850 and 1100 μm, galaxies selected at 350 μm have a similar range of far-infrared color temperatures. However, no 350 μm selected sources are reliably detected at 850 or 1100 μm. Galaxies in our sample with redshifts 1 < z < 2 show a tight correlation between the far- and mid-infrared flux densities, but galaxies at higher redshifts show a large dispersion in their mid- to far-infrared colors. This implies a limit to which the mid-IR emission traces the far-IR emission in star-forming galaxies. The 350 μm flux densities (15 < S 350 < 40 mJy) place these objects near the Herschel/SPIRE 350 μm confusion threshold, with the lower limit on the star formation rate density suggesting the bulk of the 350 μm contribution will come from less luminous infrared sources and normal galaxies. Therefore, the nature of the dominant source of the 350 μm background—star-forming galaxies in the epoch of peak star formation in the universe—could be more effectively probed using ground-based instrumen
A method is described that allows calibration and assessment of the linearity of response of an array of photomultiplier tubes. The method does not require knowledge of the photomultiplier single photoelectron response model and uses science data directly, thus eliminating the need for dedicated data sets. In this manner all photomultiplier working conditions (e.g. temperature, external fields, etc.) are exactly matched between calibration and science acquisitions. This is of particular importance in low background experiments such as ZEPLIN-III, where methods involving the use of external light sources for calibration are severely constrained.
Lebedenko VN, Araujo HM, Barnes EJ, et al., 2009, Limits on the Spin-Dependent WIMP-Nucleon Cross Sections from the First Science Run of the ZEPLIN-III Experiment, PHYSICAL REVIEW LETTERS, Vol: 103, ISSN: 0031-9007
Lebedenko VN, Araujo HM, Barnes EJ, et al., 2009, Results from the first science run of the ZEPLIN-III dark matter search experiment, Physical Review D- particles, fields, gravitation, and cosmology, Vol: 80, ISSN: 1550-7998
The ZEPLIN-III experiment in the Palmer Underground Laboratory at Boulby uses a 12 kg two-phasexenon time-projection chamber to search for the weakly interacting massive particles (WIMPs) that mayaccount for the dark matter of our Galaxy. The detector measures both scintillation and ionizationproduced by radiation interacting in the liquid to differentiate between the nuclear recoils expected fromWIMPs and the electron-recoil background signals down to 10 keV nuclear-recoil energy. An analysisof 847 kg days of data acquired between February 27, 2008, and May 20, 2008, has excluded a WIMPnucleonelastic scattering spin-independent cross section above 8:1 10 8 pb at 60 GeVc 2 with a 90%confidence limit. It has also demonstrated that the two-phase xenon technique is capable of betterdiscrimination between electron and nuclear recoils at low-energy than previously achieved by otherxenon-based experiments.
Armano M, Benedetti M, Bogenstahl J, et al., 2009, LISA Pathfinder: the experiment and the route to LISA, 7th International LISA Symposium, Publisher: IOP PUBLISHING LTD, ISSN: 0264-9381
Schulte MO, Shaul DNA, Hollington D, et al., 2009, Inertial sensor surface properties for LISA Pathfinder and their effect on test mass discharging, 7th International LISA Symposium, Publisher: IOP PUBLISHING LTD, ISSN: 0264-9381
Burenkov AA, Akimov DY, Grishkin YL, et al., 2009, Detection of a single electron in xenon-based electroluminescent detectors, PHYSICS OF ATOMIC NUCLEI, Vol: 72, Pages: 653-661, ISSN: 1063-7788
The Solar System Odyssey mission uses modern-day high-precisionexperimental techniques to test the laws of fundamental physics which determine dynamics in the solar system. It could lead to major discoveries by using demonstrated technologies and could be flown within the Cosmic Vision time frame. The mission proposes to perform a set of precision gravitation experiments from the vicinity of Earth to the outer Solar System. Its scientific objectives can be summarized as follows: (1) test of the gravity force law in the Solar System up to and beyond the orbit of Saturn; (2) precise investigation of navigation anomalies at the fly-bys; (3) measurement of Eddington’sparameter at occultations; (4) mapping of gravity field in the outer solarsystem and study of the Kuiper belt. To this aim, the Odyssey mission is built up on a main spacecraft, designed to fly up to 13 AU, with the following components: (a) a high-precision accelerometer, with bias-rejection system, measuring the deviation of the trajectory from the geodesics, that is also giving gravitational forces; (b) Ka-band transponders, as for Cassini, for a precise range and Doppler measurement up to 13 AU, with additional VLBI equipment; (c) optional laser equipment, which would allow one to improve the range and Doppler measurement, resulting in particular in an improvedmeasurement (with respect to Cassini) of the Eddington’s parameter. In this baseline concept, the main spacecraft is designed to operate beyond the Saturn orbit, up to 13 AU. It experiences multiple planetary fly-bys at Earth, Mars or Venus, and Jupiter. The cruise and fly-by phases allow the mission to achieve its baseline scientific objectives [(1) to (3) in the above list]. In addition to this baseline concept, the Odyssey mission proposes the release of the Enigmaradio-beacon at Saturn, allowing one to extend the deep space gravity test up to at least 50 AU, while achieving the scientific objective of a mapping of gravity field in
Appourchaux T, Burston R, Chen Y, et al., 2009, Astrodynamical Space Test of Relativity Using Optical Devices I (ASTROD I) - A class-M fundamental physics mission proposal for Cosmic Vision 2015-2025, Experimental Astronomy, Vol: 23, Pages: 491-527, ISSN: 1572-9508
ASTROD I is a planned interplanetary space mission with multiple goals. The primary aims are: to test general relativity with an improvement in sensitivity of over three orders of magnitude, improving our understanding of gravity and aiding the development of a new quantum gravity theory; to measure key solar system parameters with increased accuracy, advancing solar physics and our knowledge of the solar system; and to measure the time rate of change of the gravitational constant with an order of magnitude improvement and the anomalous Pioneer acceleration, thereby probing dark matter and dark energy gravitationally. It is an international project, with major contributions from Europe and China and is envisaged as the first in a series of ASTROD missions. ASTROD I will consist of one spacecraft carrying a telescope, four lasers, two event timers and a clock. Two-way, two-wavelength laser pulse ranging will be used between the spacecraft in a solar orbit and deep space laser stations on Earth, to achieve the ASTROD I goals. A second mission, ASTROD (ASTROD II) is envisaged as a three-spacecraft mission which would test General Relativity to 1 ppb, enable detection of solar g-modes, measure the solar Lense–Thirring effect to 10 ppm, and probe gravitational waves at frequencies below the LISA bandwidth. In the third phase (ASTROD III or Super-ASTROD), larger orbits could be implemented to map the outer solar system and to probe primordial gravitational-waves at frequencies below the ASTROD II bandwidth.
Alner GJ, Araujo HM, Bewick A, et al., 2009, ZEPLIN-II limits on WIMP-nucelon interactions, 8th UCLA Symposium on Sources and Detection of Dark Matter and Dark Energy in the Universe, Publisher: AMER INST PHYSICS, Pages: 218-+, ISSN: 0094-243X
Sumner TJ, 2009, First Science Results from ZEPLIN-III, 17th International Conference on Supersymmetry and the Unification of Fundamental Interactions, Publisher: AMER INST PHYSICS, Pages: 963-967, ISSN: 0094-243X
Araújo HM, Blockley J, Bungau C, et al., 2008, Measurements and simulations of muon-induced neutrons
The first measurements of the muon-induced neutron flux at the Boulby Underground Laboratory are presented. The experiment was carried out with an 0.73 tonne liquid scintillation detector that also served as an anticoincidence system for the ZEPLIN-II direct dark matter search. The experimental method exploited the delayed coincidences between high-energy muon signals and gamma-rays from radiative neutron capture on hydrogen or other elements. The muon-induced neutron rate, defined as the average number of detected neutrons per detected muon, was measured as 0.079 ±0.003 (stat.) neutrons/muon using neutron-capture signals above 0.55 MeV in a time window of 40-190 μs after the muon trigger. Accurate Monte Carlo simulations of the neutron production, transport and detection in a precisely modeled laboratory and experimental setup using the GEANT4 toolkit gave a result 1.8 times higher than the measured value. The difference greatly exceeds all statistical and systematic uncertainties. As the vast majority of neutrons detected in the current setup were produced in lead we evaluated from our measurements the neutron yield in lead as (1.31 ±0.06) × 10-3 neutrons/muon/(g/cm2) for a mean muon energy of about 260 Ge V.
Edwards B, Araujo HM, Chepel V, et al., 2008, Measurement of single electron emission in two-phase xenon, Astroparticle Physics, Vol: 30, Pages: 54-57, ISSN: 1873-2852
We present the first measurements of the electroluminescence response to the emission of single electrons in a two-phase noble gas detector. Single ionization electrons generated in liquid xenon are detected in a thin gas layer during the 31-day background run of the ZEPLIN-II experiment, a two-phase xenon detector for WIMP dark matter searches. Both the pressure dependence and magnitude of the single electron response are in agreement with previous measurements of electroluminescence yield in xenon. We discuss different photoionization processes as possible cause for the sample of single electrons studied in this work. This observation may have implications for the design and operation of future large-scale two-phase systems.
Shaul DNA, Araujo HM, Rochester GK, et al., 2008, Charge management for LISA and LISA Pathfinder, 3rd International ASTROD Symposium, Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 993-1003, ISSN: 0218-2718
Bao G, Ni W-T, Shaul DNA, et al., 2008, Further test mass charging simulations for ASTROD I, 3rd International ASTROD Symposium, Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 965-983, ISSN: 0218-2718
Araujo HM, Blockley J, Bungau C, et al., 2008, Measurements of neutrons produced by high-energy muons at the Boulby Underground Laboratory, ASTROPARTICLE PHYSICS, Vol: 29, Pages: 471-481, ISSN: 0927-6505
Shaul DNA, Araujo HM, Rochester GK, et al., 2008, Charge management for LISA and LISA Pathfinder, 3rd International ASTROD Symposium, Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 993-1003, ISSN: 0218-1940
Bao G, Ni W-T, Shaul DNA, et al., 2008, Further test mass charging simulations for ASTROD I, 3rd International ASTROD Symposium, Publisher: WORLD SCIENTIFIC PUBL CO PTE LTD, Pages: 965-983, ISSN: 0218-1940
Achterberg A, Ackermann M, Adams J, et al., 2008, Multiyear search for a diffuse flux of muon neutrinos with AMANDA-II (vol 76, artn 042008, 2007), PHYSICAL REVIEW D, Vol: 77, ISSN: 1550-7998
Alner GJ, Araujo HM, Bewick A, et al., 2008, The ZEPLIN II dark matter detector: Data acquisition system and data reduction, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, Vol: 587, Pages: 101-109, ISSN: 0168-9002
Ackermann M, Adams J, Ahrens J, et al., 2008, Search for ultra-high-energy neutrinos with amanda-II, ASTROPHYSICAL JOURNAL, Vol: 675, Pages: 1014-1024, ISSN: 0004-637X
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