Dark Matter Search at SNOLAB with
DEAP-1 and DEAP/CLEAN-3600
Bei Cai（蔡蓓）
For the DEAP/CLEAN Collaboration
Queen’s University, Canada
July 21-23, 2008
OCPA Workshop on Underground
Science
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WIMP-nucleon cross section
3600 kg LAr
CDMS-II:
~120 kg-days
(Ge)
XENON-10:
~300 kg-days
(Xe)
DEAP/CLEAN: 1,000,000 kg-days (Ar)
CDMS, arXiv:0802.3530
2
The DEAP/CLEAN Collaboration
Boston University
D. Gastler, E. Kearns
Laurentian University/ SNOLAB
B. Cleveland, F. Duncan, C. Jillings, I. Lawson
Carleton University
K. Graham
SNOLAB
I. Lawson, K. McFarlane
Los Alamos National Laboratory
C. Alexander, S. Elliott, G. Garvey, V. Gehman,
V.
Guiseppe, A. Hime, W. Louis, S. McKenney, G. Mills, K.
Rielage, L. Rodriguez, L. Stonehill, R. Van de Water, H.
White, J. Wouters
MIT
Joe Formaggio
University of New Mexico
D. Loomba
University of North Carolina
R. Henning
NIST, Boulder
K. Coakley
Queen’s University
M. Boulay, B. Cai, M. Chen, P. Harvey, J. Lidgard,
A. McDonald, P. Pasuthip, T. Pollman, P. Skensved
TRIUMF
F. Retiere
University of Alberta
A. Hallin, R. Hakobyan, K. Olsen, J. Soukup
University of South Dakota
D. Mei
University of Texas, Austin
J. Klein, S. Seibert
Yale University
L. Kastens, W. Lippincott, D. McKinsey, K. Ni, J. Nikkel
15 institutes in Canada and USA, ~ 50 researchers
The DEAP/CLEAN experiments
DEAP-1:
• 7 kg LAr prototype experiment
• Run at Queen’s for demonstration of PSD
• Installed underground at SNOLAB 2007 for continued PSD and background
studies, DM search
MicroCLEAN
• 2 kg prototype experiment at Yale University
MiniCLEAN:
• 360 kg experiment targeting DM with LAr and prototyping neon for particle
astrophysics
• Primary emphasis of US collaborators in short term
DEAP/CLEAN-3600:
• 3600 kg experiment targeting DM with LAr
• Primary emphasis of Canadian collaborators in short term
4
Argon is a good WIMP detection target
with “standard” assumptions
about the WIMP distribution
and for a 100 GeV WIMP
Rate ~ A2F
(coherent)
Loss of coherence for large nuclei
• Excellent PSD between electron recoils and
nuclear recoils
• Good scintillator (40 photons/keV)
• Inexpensive and easy to purify
• Single-phase detector, easy to scale up
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Direct WIMP detection with liquid argon
χ
40Ar
  Ar     Ar
40Ar
χ
• Energy transfer in liquid argon leads to formation of
excited dimers
• Dimer molecules are in either singlet or triplet states, and
the lifetimes are well-separated:
–
~ 6 ns for singlet state (prompt)
– ~ 1.59 µs for triplet state (delayed)
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Pulse-shape discrimination
A. Hitachi et al., Phys. Rev. B 27 (9) (1983) 5279
Fraction of dimers in singlet or triplet states depends on
the incident particle type
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DEAP-1 detector
Glass windows
Poly PMT supports
Neck connects to vacuum and
gas/liquid lines
11” x 6” (8” CF) tee
8” long acrylic guide
Acrylic vacuum chamber
ET 9390B PMT 5”
Inner surface 97% diffuse reflector,
7 kg LAr
covered with TPB wavelength shifter
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SAES getter
Ar liquefying
chamber
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Fprompt: the
discriminator
Backgrounds (g’s)
Yellow: Prompt light region
Blue: Late light region
Fprompt
Pr omptPE(150ns)

T otalPE(9s)
Signal (nuclear recoil)
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AmBe (neutron) calibration
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Backgrounds
 Neutron backgrounds
 Muon suppression at SNOLAB
 Clean materials and shielding
 Surface contamination
 Clean detector surface (resurfacer device)
 vertex reconstruction for fiducial volume
 β,γ backgrounds
 Pulse-shape discrimination
• Ar-39 is the largest source of background
• For DEAP-1, the expected βrate from Ar-39 decay is
~6×106 for 7 kg-years in 20-40 keVee
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Tagged Na-22 setup at Queen’s
Dark box
Argon
22Na
NaI
Annulus
22Na
511 keV γ
e+
e-
1.274 MeV γ
511 keV γ
13
Single PE calibration
Gain: ~107
Energy calibration using Na-22
Light yield: ~2.8 PE/keV
14
Detector
stability
15
Tagged Na-22 data
ROI
1.53x107 events in energy ROI:
(120, 240) PEs, (40, 80) keVee
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Probability of leakage
1
Pleak (Fprompt

r )

n
rn
rn
0
f (r )dr
f (r )dr
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Pulse-shape background discrimination
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DEAP-1 at SNOLAB
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Queen’s
SNOLAB (“radon-dirty” chamber)
residual backgrounds consistent with radon daughter
contamination, now reduced with glove box surface removal
x10 reduction
Livetime ~6 hrs
Livetime ~10 hrs
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Radon-222 decay rates
10 decays/m2 of air (surface labs)
100 decays/m2 of air (at SNOLAB)
Daughters from radon decay can be implanted
into surfaces
a
210-polonium alpha energy = 5.4 MeV
EN=103 keVr (sub-micron implantation)
Cryostat
Wall
LAr
a
210Po
Decay in bulk
detector tagged
by a-particle
energy
on surface
Decay from surface
releases untagged
recoiling nucleus
a
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DEAP/CLEAN-3600
detector design
veto PMTs
H2O shield
(7.8 m)
266 8” PMTs
170 cm ID
acrylic vessel
(3600 kg LAr)
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Acrylic vessel resurfacer for radon removal
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DEAP/CLEAN-3600
SNOLAB
Cube Hall
DEAP-1
SNO
SNOLAB cube hall
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MiniCLEAN
DEAP/CLEAN-3600
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Summary and outlook
• DEAP-1 has successfully demonstrated a PSD
level of 6x10-8
• Will continue running at SNOLAB for a goal of
PSD 1x10-9, and for dark matter search
• DEAP/CLEAN-3600 is being designed and has a
sensitivity of 10-46 cm2
• Begin shield tank and platform installation later
this year
• Plan to start data taking for 3600 kg in 2010
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