progress on deap
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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Mark Boulay SNOLAB V 21/8/06
Progress on DEAP
Mark BoulayCanada Research Chair in Particle AstrophysicsQueen’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 DEAP @ SNOLAB
DEAP: Dark Matter Experiment using Argon PSD
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Mark Boulay SNOLAB V 21/8/06
DEAP-1 R&D Collaboration
Queen’s UniversityM. Boulay, M. Chen, A. Hallin, J. Lidgard, R. Matthew, A.B. McDonald, K. Nicolics, P. Skensved
Carleton University K. Graham
Case Western Reserve UniversityM. Dragowsky
Los Alamos National LaboratoryA. Hime, D. Mei, K. Rielage, L. Stonehill, J. Wouters
SNOLABF. Duncan, I. Lawson, C.J. Jillings
Yale UniversityD. McKinsey, J. Nikkel
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Mark Boulay SNOLAB V 21/8/06
Direct WIMP detection in terrestrial experiment
•WIMPs can elastically scatter in detector producing nuclear recoils
40Ar
40Ar
•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
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Mark Boulay SNOLAB V 21/8/06
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 onionization density along track, and thus on incident particletype
Net effect is a difference in the photon emission versus timecurve for events and for nuclear recoils
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Mark Boulay SNOLAB V 21/8/06
scintillation pulse-shape analysis for discrimination of e- vs nuclear recoils-> no electron-drift
http://arxiv.org/astro-ph/0411358
DEAP : Dark-matter Experiment with Argon PSD
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Mark Boulay SNOLAB V 21/8/06
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 forusing this technique to mitigate backgrounds
DEAP experimental program focused on determining and measuring background requirements for large (1-tonne) experiment
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Mark Boulay SNOLAB V 21/8/06
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
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Mark Boulay SNOLAB V 21/8/06
Discrimination in liquid argon
O(1in 105) consistentwith random coincidencewith intrinsicbackground(preliminary)
<pe> = 60 corresponds to 10 keV with 75% coverage
<pe> = 60
preliminary
LANL cryostat
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Mark Boulay SNOLAB V 21/8/06
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
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Mark Boulay SNOLAB V 21/8/06
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 andGas/liquid lines
DEAP-1 design
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Mark Boulay SNOLAB V 21/8/06
DEAP-1 (7 kg LAr) at Queen’s
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Mark Boulay SNOLAB V 21/8/06
DEAP-1 LAr calibration data from run @ Queen’s
PE
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Mark Boulay SNOLAB V 21/8/06
WIMP search region in DEAP-1
WIMP search region
unshielded run on surface at Queen’s
Need to shield detector and move UGto SNOLAB
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Mark Boulay SNOLAB V 21/8/06
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Mark Boulay SNOLAB V 21/8/06
What we’re up against… Backgrounds in DEAP
Detector materials bulk U, Th, K
Liquid argon target39Ar, Kr, U, Th
Laboratory wallsU,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 assayclean components
argon purificationand PSD
Shielding for neutrons and ’s
SNOLAB (depth)
Minimize surface plate-out, fit event vertices for fiducial volume
DEAP-1
DEAP-3
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Mark Boulay SNOLAB V 21/8/06
-emitters (radon-daughters) plated out on detector surfaces are a dangerous background
210Po on surface
Decay in bulk detectortagged by -particleenergy
Decay from surface releasesuntagged recoiling nucleus
Cryostat wall
LAr
WLS coating
cf. SNO NCDs: residual surfacecontamination of 1/m2/day 0.1 mHz for 1-tonne expt
(irreducible Radon emanation)
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Mark Boulay SNOLAB V 21/8/06
Purified argon gas, no source
(alpha’s)
(muon flux on lightguides is 7.8 Hz@1/cm2/min)
Measurement of surface alpha activity with argon gas
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Mark Boulay SNOLAB V 21/8/06
Summary of materials assayed for DEAP-1 SNOLAB Ge counter (see Ian Lawson’s talk)
Material 232Th 238U 40K other
(ppb) (ppb) (ppm)
stainless (chamber,flanges,neck)
1.9 ± 0.14 0.51 ± 0.04 218 ± 69 60Co
Al (80/20)
dark box332 ± 12 762 ± 58 2956 ± 1216
Al sheet (dark box)
248 ± 1 788 ± 13 none 235U, 60Co
rubber gasket 6049 ± 147 1547 ± 133 828± 45
circuit boards (PMT bases)
5309 ± 135 1439 ± 162 1005 ± 57 235U
welding rods 76 ± 6 39 ± 25 0.4 ± 3 60Co
9390UL PMTs
(Electron Tubes)31 ± 11 28 ± 19 60 ± 16
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Mark Boulay SNOLAB V 21/8/06
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Mark Boulay SNOLAB V 21/8/06
Backgrounds in DEAP-1
Source (Hz)
Nuclear recoil
(events/year)
Detector materials ≤ 1 ≤ 1
39Ar 1.5 0
Lab walls < 1 < 1
Cosmic rays < 1 < 1
Rn plate-out <<1 Hz 17 mHz
Surface ? ?
Total (events/year)
5 x 10 7 5 x 10 5
need tomeasure
need 108 PSD need position reconstruction to remove surface events
need toreduce
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Mark Boulay SNOLAB V 21/8/06
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
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Mark Boulay SNOLAB V 21/8/06
DEAP-1 proposed location at SNO
space limits shielding design
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Mark Boulay SNOLAB V 21/8/06
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
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Mark Boulay SNOLAB V 21/8/06
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)
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Mark Boulay SNOLAB V 21/8/06
Conceptual design for DEAP-3
~10 cm position resolutionallows reduction of 0.5 mHzsurface contamination
1-tonne fiducial LAr forsensitive WIMP search
$2.5 M capital
500 PMTs
Needs 5 m diameter liquid shielding tank, explore possibility of overlap with DEAP-1
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Mark Boulay SNOLAB V 21/8/06
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)