SNOLAB V 21/8/06 Mark Boulay Progress on DEAP Mark Boulay Canada Research Chair in Particle Astrophysics Queen’s University 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 SNOLAB DEAP: Dark Matter Experiment using Argon PSD

SNOLAB V 21/8/06 Mark Boulay 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 A.Hime, D. Mei, K. Rielage, L. Stonehill, J. Wouters SNOLAB F. Duncan, I. Lawson, C.J. Jillings Yale University D. McKinsey, J. Nikkel

SNOLAB V 21/8/06 Mark Boulay Direct WIMP detection in terrestrial experiment WIMPs can elastically scatter in detector producing nuclear recoils  40 Ar  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

SNOLAB V 21/8/06 Mark Boulay 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  s 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  events and for nuclear recoils

SNOLAB V 21/8/06 Mark Boulay scintillation pulse- shape analysis for discrimination of e- vs nuclear recoils -> no electron-drift DEAP : Dark-matter Experiment with Argon PSD

SNOLAB V 21/8/06 Mark Boulay 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

SNOLAB V 21/8/06 Mark Boulay Some advantages of LAr Inexpensive : 10 kg = 25$ of LAr Good light yield, 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

SNOLAB V 21/8/06 Mark Boulay Discrimination in liquid argon O(1in 10 5 ) consistent with random coincidence with intrinsic background (preliminary) = 60 corresponds to 10 keV with 75% coverage = 60 preliminary LANL cryostat

SNOLAB V 21/8/06 Mark Boulay 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

SNOLAB V 21/8/06 Mark Boulay ET 9390 PMT 5” 6” acrylic guide 11” x 6” (8” CF) tee Acrylic vacuum chamber Quartz windows poly PMT supports inner surface 97% diffuse reflector, Covered with TPB wavelength shifter Neck connects to vacuum and Gas/liquid lines DEAP-1 design

SNOLAB V 21/8/06 Mark Boulay DEAP-1 (7 kg LAr) at Queen’s

SNOLAB V 21/8/06 Mark Boulay DEAP-1 LAr calibration data from Queen’s PE

SNOLAB V 21/8/06 Mark Boulay WIMP search region in DEAP-1 WIMP search region unshielded run on surface at Queen’s Need to shield detector and move UG to SNOLAB

SNOLAB V 21/8/06 Mark Boulay

SNOLAB V 21/8/06 Mark Boulay What we’re up against… Backgrounds in DEAP Detector materials bulk U, Th, K Liquid argon target 39 Ar, Kr, U, Th Laboratory walls U,Th, K Radon daughter plate-out Surfaces and optical effects Cosmic rays fast neutrons  -  bkgs are reduced with PSD Neutron and nuclear recoils bkgs are reduced with clean materials and shielding Surface bkgs are reduced using vertex positioning (large expt) select and assay clean components argon purification and PSD Shielding for neutrons and  ’s SNOLAB (depth) Minimize surface plate-out, fit event vertices for fiducial volume DEAP-1 DEAP-3

SNOLAB V 21/8/06 Mark Boulay  -emitters (radon-daughters) plated out on detector surfaces are a dangerous background 210 Po on surface Decay in bulk detector tagged by  -particle energy Decay from surface releases untagged recoiling nucleus Cryostat wall LAr   WLS coating cf. SNO NCDs: residual surface contamination of 1/m 2 /day 0.1 mHz for 1-tonne expt (irreducible Radon emanation)

SNOLAB V 21/8/06 Mark Boulay Purified argon gas, no source (alpha’s) (muon flux on light guides is 7.8 1/cm 2 /min) Measurement of surface alpha activity with argon gas

SNOLAB V 21/8/06 Mark Boulay Summary of materials assayed for DEAP-1 SNOLAB Ge counter (see Ian Lawson’s talk) Material 232 Th 238 U 40 Kother (ppb) (ppm) stainless (chamber,flanges, neck) 1.9 ± ± ± Co Al (80/20) dark box 332 ± ± ± 1216 Al sheet (dark box) 248 ± 1788 ± 13none 235 U, 60 Co rubber gasket 6049 ± ± ± 45 circuit boards (PMT bases) 5309 ± ± ± U welding rods 76 ± 639 ± ± 3 60 Co 9390UL PMTs (Electron Tubes) 31 ± 1128 ± 1960 ± 16

SNOLAB V 21/8/06 Mark Boulay

SNOLAB V 21/8/06 Mark Boulay Backgrounds in DEAP-1 Source   (Hz) Nuclear recoil (events/year) Detector materials≤ 1 39 Ar Lab walls< 1 Cosmic rays< 1 Rn plate-out<<1 Hz 17 mHz Surface ? ? Total (events/year) 5 x x 10 5 need to measure need 10 8 PSD need position reconstruction to remove surface events need to reduce

SNOLAB V 21/8/06 Mark Boulay DEAP-1 shielding design 60 cm water “cubes” figure F. Duncan reduces (alpha,n) UG (from rock wall) to < 1 per year evaluating requirements for  shielding, radon

SNOLAB V 21/8/06 Mark Boulay DEAP-1 proposed location at SNO space limits shielding design

SNOLAB V 21/8/06 Mark Boulay 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

SNOLAB V 21/8/06 Mark Boulay 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)

SNOLAB V 21/8/06 Mark Boulay 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

SNOLAB V 21/8/06 Mark Boulay 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)