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Dark matter searches at Boulby mine
Nuclear Physics B (Proc. Suppl.) 143 (2005) 552 www.elsevierphysics.com
Dark matter searches at Boulby mine V. A. Kudryavtseva for the Boulby Dark Matter Collaboration a
Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, UK
The Boulby Dark Matter Collaboration is running WIMP search experiments at Boulby Mine (North Yorkshire, UK) at a depth of 2800 m w. e. Three major programmes have been pursued so far: i) the NAIAD experiment (an array of NaI(Tl) crystals) is completed; ii) detectors based on liquid xenon (ZEPLIN), which have high background discrimination power, have been developed and are either running or being commissioned, iii) a low-pressure gas TPC (DRIFT) with a potential of directional sensitivity has been constructed and is operating at Boulby.
ZEPLIN I consisted of a 3.2 kg fiducial mass liquid Xe scintillator viewed by 3 PMTs and surrounded by one tonne of organic scintillator used as a an active veto and neutron shield [1]. The mean time constant of scintillation pulses in xenon were found to be very much different (by about a factor of 2 at low energies) for electron and nuclear recoils. Detector calibration was done at the surface using a neutron source and ambient neutrons, which produce nuclear recoils, expected also from WIMP-nucleus interactions, and a gamma-ray source, which produces electron recoils via Compton scattering, similar to the typical background signal. Based on the absence of the nuclear recoils in the underground data, 0920-5632/$ – see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.nuclphysbps.2005.01.217
the 90% C.L. limit on their rate was calculated. The preliminary limits on the spin-independent WIMP-nucleon cross-section from 293 kg×days of data are shown in the Figure in comparison with NAIAD and some other world-best limits [1]. The two-phase Xe detectors ZEPLIN II and III will measure the ratio of ionisation to scintillation using an electric field to extract ionisation electrons from the liquid into the gas phase. For a given primary (scintillation) amplitude an electron recoil will produce a much larger secondary (ionisation) signal than a nuclear recoil. The detectors will be installed at Boulby in 20042005 and will have a sensitivity to WIMPs of ∼10−7 − 10−8 pb at ∼100 GeV WIMP mass. R&D for a one tonne, two-phase Xe detector ZEPLIN-MAX has been started with the intention of building the detector in the next few years. DRIFT is designed to search for a sidereal variation of nuclear recoil directions that could provide a definitive WIMP signature. DRIFT I consists of a 1 m3 low pressure (40 Torr) TPC filled with electro-negative CS2 gas and is capable of measuring the components of recoil tracks in addition to their energy. DRIFT I has an electron recoil rejection power >105 based on the difference in ionisation density and track length. The objective of the DRIFT programme is to build DRIFT II, consisting of several modules with better position sensitivity and lower energy threshold compared to DRIFT I, and to scale-up modules towards a target mass of 100 kg (DRIFT III) reaching a sensitivity of ∼10−9 pb. REFERENCES 1. See talks at the 6th UCLA Symposium (Marina del Rey, USA, Feb. 18-20, 2004), http://www.physics.ucla.edu/hep/dm04/.
Dark matter searches at Boulby mine V. A. Kudryavtseva for the Boulby Dark Matter Collaboration a
Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, UK
The Boulby Dark Matter Collaboration is running WIMP search experiments at Boulby Mine (North Yorkshire, UK) at a depth of 2800 m w. e. Three major programmes have been pursued so far: i) the NAIAD experiment (an array of NaI(Tl) crystals) is completed; ii) detectors based on liquid xenon (ZEPLIN), which have high background discrimination power, have been developed and are either running or being commissioned, iii) a low-pressure gas TPC (DRIFT) with a potential of directional sensitivity has been constructed and is operating at Boulby.
ZEPLIN I consisted of a 3.2 kg fiducial mass liquid Xe scintillator viewed by 3 PMTs and surrounded by one tonne of organic scintillator used as a an active veto and neutron shield [1]. The mean time constant of scintillation pulses in xenon were found to be very much different (by about a factor of 2 at low energies) for electron and nuclear recoils. Detector calibration was done at the surface using a neutron source and ambient neutrons, which produce nuclear recoils, expected also from WIMP-nucleus interactions, and a gamma-ray source, which produces electron recoils via Compton scattering, similar to the typical background signal. Based on the absence of the nuclear recoils in the underground data, 0920-5632/$ – see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.nuclphysbps.2005.01.217
the 90% C.L. limit on their rate was calculated. The preliminary limits on the spin-independent WIMP-nucleon cross-section from 293 kg×days of data are shown in the Figure in comparison with NAIAD and some other world-best limits [1]. The two-phase Xe detectors ZEPLIN II and III will measure the ratio of ionisation to scintillation using an electric field to extract ionisation electrons from the liquid into the gas phase. For a given primary (scintillation) amplitude an electron recoil will produce a much larger secondary (ionisation) signal than a nuclear recoil. The detectors will be installed at Boulby in 20042005 and will have a sensitivity to WIMPs of ∼10−7 − 10−8 pb at ∼100 GeV WIMP mass. R&D for a one tonne, two-phase Xe detector ZEPLIN-MAX has been started with the intention of building the detector in the next few years. DRIFT is designed to search for a sidereal variation of nuclear recoil directions that could provide a definitive WIMP signature. DRIFT I consists of a 1 m3 low pressure (40 Torr) TPC filled with electro-negative CS2 gas and is capable of measuring the components of recoil tracks in addition to their energy. DRIFT I has an electron recoil rejection power >105 based on the difference in ionisation density and track length. The objective of the DRIFT programme is to build DRIFT II, consisting of several modules with better position sensitivity and lower energy threshold compared to DRIFT I, and to scale-up modules towards a target mass of 100 kg (DRIFT III) reaching a sensitivity of ∼10−9 pb. REFERENCES 1. See talks at the 6th UCLA Symposium (Marina del Rey, USA, Feb. 18-20, 2004), http://www.physics.ucla.edu/hep/dm04/.