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Progress on DEAP

Progress on DEAP. DEAP: D ark Matter E xperiment using A rgon P SD. Scintillation PSD with LAr DEAP-1: 7 kg LAr cryostat, low-background, low-threshold detector (U/G in SNOLAB fall ‘06) Summary of backgrounds in DEAP-1 Materials assays

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Progress on DEAP

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  1. Progress on DEAP DEAP: Dark Matter Experiment using Argon PSD • Scintillation PSD with LAr • DEAP-1: 7 kg LAr cryostat, low-background, • low-threshold detector (U/G in SNOLAB fall ‘06) • Summary of backgrounds in DEAP-1 • Materials assays • Shielding design • Schedule for DEAP-1 • Plans for 1-tonne DM search with DEAP @ SNOLAB Mark Boulay Canada Research Chair in Particle Astrophysics Queen’s University

  2. DEAP-1 R&D Collaboration • Queen’s University • M. Boulay, M. Chen, A. Hallin, J. Lidgard, R. Matthew, • A.B. McDonald, K. Nicolics, P. Skensved • Carleton University • K. Graham • Case Western Reserve University • M. Dragowsky • Los Alamos National Laboratory • Hime, D. Mei, K. Rielage, L. Stonehill, J. Wouters • SNOLAB • F. Duncan, I. Lawson, C.J. Jillings • Yale University • D. McKinsey, J. Nikkel

  3. 40Ar c 40Ar c Direct WIMP detection in terrestrial experiment • WIMPs can elastically scatter in detectorproducingnuclear recoils • Rate in terrestrial detector depends on WIMP mass and WIMP-nucleon interaction cross-section • Low-energy recoils with E ~ 10 keV, low threshold • Easy to detect nuclear recoils, experimental challenge is to detect small number of WIMP nuclear recoils in a sea of backgrounds

  4. Scintillation in liquid argon • ionizing radiation leads to formation of excited dimers in argon (Ar*2) • dimers are produced in either singlet or triplet excited states • decays have characteristic times, and can result • in photon emission • ~ 2 ns for singlet state (prompt) • 1.6 us for triplet state (delayed) • Fraction of dimers in singlet versus triplet state depends on • ionization density along track, and thus on incident particle • type • Net effect is a difference in the photon emission versus time • curve for g/b events and for nuclear recoils

  5. http://arxiv.org/astro-ph/0411358 scintillation pulse-shape analysis for discrimination of e- vs nuclear recoils -> no electron-drift DEAP : Dark-matter Experiment with Argon PSD

  6. Idea is to use scintillation photons only for discrimination in DEAP… …allows for simple and clean detector design and a more easily scalable experiment Preliminary simulations and data show promise for using this technique to mitigate backgrounds DEAP experimental program focused on determining and measuring background requirements for large (1-tonne) experiment

  7. Some advantages of LAr • Inexpensive : 10 kg = 25$ of LAr • Good light yield, 40000 photons/MeV = good resolution • Used extensively, very large experiments underground • Easily accessible temperature (~85 K) • Same requirements as LN for cryogenic components • Liquid experiment can be continuously or periodically • purified Allows simple, inexpensive, scalable design: O(2000$ per kg) fiducial mass

  8. Discrimination in liquid argon <pe> = 60 O(1in 105) consistent with random coincidence with intrinsic background (preliminary) preliminary LANL cryostat <pe> = 60 corresponds to 10 keV with 75% coverage

  9. DEAP-1 detector A 7 kg LAr cryostat to: • develop high light yield and low threshold detector • demonstrate PSD at low threshold (10 keV) • develop low background detector and verify background calculations • measure residual surface backgrounds • define requirements for large (1-tonne) experiment

  10. DEAP-1 design Neck connects to vacuum and Gas/liquid lines Quartz windows 11” x 6” (8” CF) tee poly PMT supports 6” acrylic guide Acrylic vacuum chamber ET 9390 PMT 5” inner surface 97% diffuse reflector, Covered with TPB wavelength shifter

  11. DEAP-1 (7 kg LAr) at Queen’s

  12. DEAP-1 LAr calibration data from run @ Queen’s PE

  13. WIMP search region in DEAP-1 Need to shield detector and move UG to SNOLAB WIMP search region unshielded run on surface at Queen’s

  14. What we’re up against… Backgrounds in DEAP Detector materials bulk U, Th, K select and assay clean components b-g bkgs are reduced with PSD Liquid argon target 39Ar, Kr, U, Th argon purification and PSD Neutron and nuclear recoils bkgs are reduced with clean materials and shielding Laboratory walls U,Th, K Shielding for neutrons and g’s SNOLAB (depth) Cosmic rays fast neutrons Surface bkgs are reduced using vertex positioning (large expt) Radon daughter plate-out Minimize surface plate-out, fit event vertices for fiducial volume DEAP-1 Surfaces and optical effects DEAP-3

  15. LAr Cryostat wall Decay in bulk detector tagged by a-particle energy a 210Po on surface Decay from surface releases untagged recoiling nucleus a WLS coating a-emitters (radon-daughters) plated out on detector surfaces are a dangerous background cf. SNO NCDs: residual surface contamination of 1/m2/day 0.1 mHz for 1-tonne expt (irreducible Radon emanation)

  16. Measurement of surface alpha activity with argon gas (muon flux on light guides is 7.8 Hz@ 1/cm2/min) (alpha’s) Purified argon gas, no source

  17. Summary of materials assayed for DEAP-1 SNOLAB Ge counter (see Ian Lawson’s talk)

  18. Backgrounds in DEAP-1 need to reduce need to measure need position reconstruction to remove surface events need 108 PSD

  19. DEAP-1 shielding design 60 cm water “cubes” reduces (alpha,n) UG (from rock wall) to < 1 per year figure F. Duncan evaluating requirements for g shielding, radon

  20. DEAP-1 proposed location at SNO space limits shielding design

  21. Timeline for DEAP-1 (7 kg LAr) • Commission shield, reduce surface contamination with radon free glove box system, and calibrate on surface (2 months) • Submit first RTP to SNO/SNOLAB (End of August 2006) • Deploy shielded detector in SNOLAB (fall 2006) • Determine ultimate residual background level in WIMP search region

  22. Plans in for large (fiducialized) liquid argon detector • Will use DEAP-1 to define background reduction needed for tonne-scale experiment • NSERC project grant proposal for fall 2006 ($2.5M CAD capital+operating total project cost) for construction start 2007 • Currently Queen’s+Carleton+SNOLAB (Boulay, Chen, Hallin, McDonald, Graham, Duncan, Lawson, Jillings)

  23. Conceptual design for DEAP-3 ~10 cm position resolution allows reduction of 0.5 mHz surface contamination 1-tonne fiducial LAr for sensitive WIMP search $2.5 M capital 500 PMTs Needs 5 m diameter liquid shielding tank, explore possibility of overlap with DEAP-1

  24. Conclusions • Liquid argon promising target for DM • Inexpensive for large, sensitive DM search • DEAP-1 built, commissioning shield for U/G deployment fall 2006 • Will further evaluate PSD and backgrounds UG • Proposal fall 2006 to NSERC for $2.5M capital project for 2007 funds (5 m diameter footprint)

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