Dark Matter Experiments at Boulby mine The Boulby Dark Matter Collaboration Imperial College of Science, Technology and Medicine, London: B. Ahmed, A. Bewick, D. Davidge, J. V. Dawson, A. S. Howard, W. G. Jones, M. K. Joshi, V. Lebedenko, I. Liubarsky, R. LЯscher, T. J. Sumner, J. J. Quenby; Rutherford Appleton Laboratory: G. J. Alner, S. P. Hart, I. Ivaniouchenkov, J. D. Lewin, R. M. Preece, N. J. T. Smith, P.F. Smith; Queen Mary, University of London: J. C. Barton; University of Sheffield: M. J. Carson, T. Gamble, R. Hollingworth, V. A. Kudryavtsev, T. B. Lawson, P. K. Lightfoot, J. E. McMillan, B. Morgan, G. Nicklin, S. M. Paling, J. W. Roberts, M. Robinson, N. J. C. Spooner, D R. Tovey; Occidental College: D. P. Snowden-Ifft, J. Kirkpatrick; Temple University: C. J. Martoff, R. Ayad; UCLA: D. B. Cline, H. Wang, Y. Seo, M. Atac, F. Sergiampietri; LLNL: W. W. Craig; Columbia University: C. J. Hailey, M. Sileo, P. Graham, J. Hong ; CERN/ICGF-CNR-Torino/INFN-Padova: P. Picchi, F. Pietropaolo, L. Periale, G. Mannocchi, C. Castagnoli; ITEP, Moscow: D. Akimov, A. Danilov; Texas A&M University: J. T. White, J. Gao; UMSNH, Morelia, Mexico: U. Cotti, M. Reyes, L. Villasenor; CINVESTAV, Mexico City: A. Zepeda NAIAD - NaI Advanced DetectorZEPLIN - ZonEd Proportional scintillation in LIquid Noble gases DRIFT - Directional Recoil Identification from Tracks Motivation: Two different targets with high and low masses Sensitive to both spin-independent and spin-dependent WIMP-nucleus interactions Aimed to confirm or refute annual modulation signal, claimed by DAMA, with similar type detectors (NaI) but different analysis technique Can be also used as a diagnostic array to study backgrounds and systematic effects for other dark matter experiments at Boulby «NAIAD» by John William Waterhouse Signal discrimination: Pulse Shape Analysis is used to discriminate between nuclear recoils, which can be caused by WIMP interactions, and electron recoils due to gamma background Light yield determines the discrimination power of the pulse shape analysis Running unencapsulated crystals requires stability of the light yield Each crystal is calibrated with gamma and neutron sources Integrated pulses are fitted to an exponential Time constant distributions are fitted to the log(Gauss) function (or two log(Gauss) functions in case of two components) + PMT noise In real data we search for the second (fast) component with known parameters gamma source neutron source electron recoils from gamma background nuclear recoils Compton calibration with gamma source - electron recoils Data shows one population of scintillation pulses + PMT noise 6-7 keV7-8 keV UKDMC, measured for DM77 Sakai, IEEE Transactions on Nuclear Science, vol. NS-34, cm crystal DAMA, preprint INFN/AE-00/10, 2000 Energy calibration and energy resolution NAIAD results 6 crystals are currently running at Boulby. Data from 4 crystals have been analysed to set new limits on WIMP-nucleon spin-independent interactions; total exposure = 10.6 kg x years. Significant improvement over previous limits (1996) has been achieved due to higher light yield and better discrimination. Extensive studies of NaI(Tl) crystals and their response to various radiations have been performed (energy calibration and resolution, gamma and neutron calibrations etc.). Pulse shape analysis has been proven to work in NaI detectors and to produce reliable limits. DAMA can use PSA to confirm or refute the positive signal found in annual modulation analysis. 1 ton liquid PXE scintillator Veto Xe Target lined with PTFE reflector Xe filled Turrets capped by quartz windows 3.7kg liquid Xe Xe lineCoolant line Photomultiplier Vacuum pump on insulation jacket T 90 / ns Boulby underground laboratory metres underground in the salt and potash mine Calibrations with : Various gamma sources Am-Be neutron/gamma source Various measurements of pulse shape Fitted exponential,  Mean photon arrival time,  90 Time to reach 70%,  70 Distributed as a gamma function in 1/X ZEPLIN I - Liquid Xe Singlet/triplet ratio differs for nuclear and electron recoils Recombination is relevant only for electron recoils (=> t~45ns) Pulse Shape Analysis is applied Noise cuts (asymmetry cuts, fiducial volume cuts) are applied using projection of normalised amplitude from each PMT onto a plane - S 3 cut Background rejection by Compton veto (liquid scintillator) and S 3 cut 22 Poisson 27 days of live time = 90 kg x days gamma calibration data from contemporaneous veto events Gamma function fit to 1/  distribution Analysis:  2 in high statistics region, Poisson in tail ZEPLIN II - Double Phase Xe Detector - under construction (30 kg) Xe detector with field: Electric field prevents recombination and allows the measurement of the ionisation yield. For electron recoils the track is less dense and the electric field is more efficient in separating electrons from ions. Ionisation electron drifts towards a high field region in the gas phase. Electro-luminescence light from the avalanche process around a multi-wire plane is detected as 2nd scintillation. Active volume Gas phase  Electro- luminescence Primary- Scintillation nuclear recoils: high primary scintillation, low ionisation yield (2nd scintillation) electron recoils: low primary scintillation, high ionisation yield (2nd scintillation) 3 modules 80 kg target 4 sub- units shielding ZEPLIN III and ZEPLIN MAX - Double Phase Xe Detector with high electric field - at R&D phase alpha population gradually moves closer to vertical as the E-field is increased Primary vs secondary scintillation for alphas for several values of electric field The effect of increasing the voltage from 7kV to 12kV Towards 1 ton Xe detector ZEPLIN MAX Poster made by V. A. Kudryavtsev, University of Sheffield, UK UKDMC web-site: hepwww.rl.ac.uk/ukdmc/ New Caverns at Boulby 50 m New surface lab Directionality: WIMP velocity distribution in the Earth’s frame is strongly peaked in the direction of the solar motion – A WIMP ‘wind’ A strong signature - sidereal variation of the directions of recoil tracks Distribution of recoil directions in galactic coordinates is peaked in direction opposite to solar motion DRIFT concept -low pressure (40 torr) gas Time Projection Chamber Ionisation tracks > 1 mm. Electrons are drifted in an electric field to the x-y readout region. Drift time measurements provide z-co-ordinates of the tracks. This allows full 3D reconstruction of events (track length, energy, orientation) Simulation of tracks from different particles in a low pressure gas Negative ion DRIFT: electron capture by electronegative gas reduces track diffusion (~0.5 mm at 0.5 m drift length) Electric Field Scattered WIMP MWPC Readout Plane Cathode Drift direction CS 2 Recoil Atom DRIFT I - first directional WIMP detector DRIFT I at Boulby Large scale DRIFT design High resolution readout WIMP-nucleon cross-section, pb NaI 1996 NAIAD/Xe 2002/3 Xe 2003/4 DRIFT 2004/5 Xe 2005 Xe-MAX WIMP mass, GeV ZEPLIN II DRIFT II and DRIFT III - towards a 100 kg directional detector Vacuum Vessel Optics Modules Projected sensitivity of WIMP detectors at Boulby Preliminary limits from ZEPLIN I ZEPLIN I: results Response of a prototype detector to gammas and neutrons C recoils S recoils gammas recoil discrimination