D. R. Tovey

A New model independent method for extracting spin dependent (cross-section) limits from dark matter searches

Abstract A new method is proposed for extracting limits on spin-dependent WIMP-nucleon interaction cross sections from direct detection dark matter experiments. The new method has the advantage that the limits on individual WIMP-proton and WIMP-neutron cross sections for a given WIMP mass can be combined in a simple way to give a model-independent limit on the properties of WIMPs scattering from both protons and neutrons in the target nucleus. Extension of the technique to the case of a target material consisting of several different species of nuclei is discussed.

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 WIMP cross-sections from the NAIAD experiment at the Boulby Underground Laboratory

The NAIAD experiment (NaI Advanced Detector) for WIMP dark matter searches at the Boulby Underground Laboratory (North Yorkshire, UK) ran from 2000 until 2003. A total of 44.9 kg x years of data collected with 2 encapsulated and 4 unencapsulated NaI(Tl) crystals with high light yield were included in the analysis. We present final results of this analysis carried out using pulse shape discrimination. No signal associated with nuclear recoils from WIMP interactions was observed in any run with any crystal. This allowed us to set upper limits on the WIMP-nucleon spin-independent and WIMP-proton spin-dependent cross-sections. The NAIAD experiment has so far imposed the most stringent constraints on the spin-dependent WIMP-proton cross-section.

Measuring the SUSY mass scale at the LHC

Abstract An effective mass scale M susy eff for supersymmetric particles is defined and techniques for its measurement at the LHC discussed. Monte Carlo results show that, for jets+ E T miss events, a variable constructed from the scalar sum of the transverse momenta of all reconstructed jets together with E T miss provides in many cases the most accurate measurement of M susy eff (intrinsic precision ∼2.1% for mSUGRA models). The overall precision with which M susy eff could be measured after given periods of LHC running and for given classes of SUSY models is calculated. The technique is extended to measurements of the total SUSY particle production cross section σ susy .

The evaporative cooling system for the ATLAS inner detector

This paper describes the evaporative system used to cool the silicon detector structures of the inner detector sub-detectors of the ATLAS experiment at the CERN Large Hadron Collider. The motivation for an evaporative system, its design and construction are discussed. In detail the particular requirements of the ATLAS inner detector, technical choices and the qualification and manufacture of final components are addressed. Finally results of initial operational tests are reported. Although the entire system described, the paper focuses on the on-detector aspects. Details of the evaporative cooling plant will be discussed elsewhere.

Neutron background in large-scale xenon detectors for dark matter searches

Abstract Simulations of the neutron background for future large-scale particle dark matter detectors are presented. Neutrons were generated in rock and detector elements via spontaneous fission and (α,n) reactions, and by cosmic-ray muons. The simulation techniques and results are discussed in the context of the expected sensitivity of a generic liquid xenon dark matter detector. Methods of neutron background suppression are investigated. A sensitivity of 10 −9 –10 −10 pb to WIMP-nucleon interactions can be achieved by a tonne-scale detector.

Measurement of scintillation efficiencies and pulse-shapes for nuclear recoils in NaI(Tl) and CaF2(Eu) at low energies for dark matter experiments

Abstract Measurements have been performed with a 2.85 MeV mono-energetic neutron beam of relative scintillation efficiency and pulse-shape for nuclear and electron recoils in NaI(Tl) and CaF2(Eu). Scintillation efficiencies in NaI(Tl) relative to 60 keV gamma events were found to be 27.5±1.8% for Na recoils (recoil energy Erec>4 keV) and 8.6±0.7% for I recoils (Erec>10 keV). Relative scintillation efficiencies in CaF2(Eu) for Ca and F recoils show some evidence for a fall with energy (17% to 8% for F) for 10 keV 〈 t i 〉 of 263±15 ns for Na events (visible energy Evis in the range 2–8 keV and 272±10 ns for I events (2 keV 〈 t i 〉 of 4 keV 〈 t i 〉 for 2 keV

NaI dark matter limits and the NAIAD array – a detector with improved sensitivity to WIMPs using unencapsulated NaI

Re-analysis of published data from the UKDMC NaI Tl dark matter experiment is presented using latest spin factors and comparison is made with the sensitivity predicted for NAIAD, a 100 kg NaI detector concept based on unencapsulated . NaI Tl . We present experimental results and Monte Carlo simulations for NAIAD and show that a factor of 1.5-2 improvement in energy threshold is achievable over conventional NaI dark matter detectors with consequent ; 50% improvement in nuclear recoil discrimination at 10 keV. An overall improvement in sensitivity to spin dependent WIMP interactions of factor 50, based on 100 kg = yrs of data, is predicted relative to previous UKDMC limits. q 2000 Published by Elsevier Science B.V. All rights reserved.

CsI(Tl) for WIMP dark matter searches

Abstract We report a study of CsI(Tl) scintillator to assess its applicability in experiments to search for dark matter particles. Measurements of the mean scintillation pulse shapes due to nuclear and electron recoils have been performed. We find that, as with NaI(Tl), pulse shape analysis can be used to discriminate between electron and nuclear recoils down to 4 keV. However, the discrimination factor is typically 10–15% better than in NaI(Tl) above 4 keV. The quenching factor for caesium and iodine recoils was measured and found to increase from 11% to ∼17% with decreasing recoil energy from 60 to 12 keV. Based on these results, the potential sensitivity of CsI(Tl) to dark matter particles in the form of neutralinos was calculated. We find an improvement over NaI(Tl) for the spin-independent WIMP–nucleon interactions up to a factor of 5 assuming comparable electron background levels in the two scintillators.

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.