July 21-23, 2008 OCPA Workshop on Underground Science

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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

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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

The DEAP/CLEAN CollaborationBoston University

D. Gastler, E. Kearns

Carleton UniversityK. Graham

Los Alamos National LaboratoryC. 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

MITJoe Formaggio

NIST, BoulderK. Coakley

Queen’s UniversityM. Boulay, B. Cai, M. Chen, P. Harvey, J. Lidgard, A. McDonald, P. Pasuthip, T. Pollman, P. Skensved

TRIUMFF. Retiere

Laurentian University/ SNOLABB. Cleveland, F. Duncan, C. Jillings, I. Lawson

SNOLAB I. Lawson, K. McFarlane

University of AlbertaA. Hallin, R. Hakobyan, K. Olsen, J. Soukup

University of New MexicoD. Loomba

University of North CarolinaR. Henning

University of South DakotaD. Mei

University of Texas, AustinJ. Klein, S. Seibert

Yale UniversityL. Kastens, W. Lippincott, D. McKinsey, K. Ni, J. Nikkel

15 institutes in Canada and USA, ~ 50 researchers

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The DEAP/CLEAN experimentsDEAP-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

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Argon is a good WIMP detection target

• 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

with “standard” assumptions about the WIMP distribution and for a 100 GeV WIMP

Rate ~ A2F (coherent)

Loss of coherence for large nuclei

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χ 40Ar

40Ar

χ

rAAr

Direct WIMP detection with liquid argon

• 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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Fraction of dimers in singlet or triplet states depends on the incident particle type

Pulse-shape discrimination

A. Hitachi et al., Phys. Rev. B 27 (9) (1983) 5279

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ET 9390B PMT 5”8” long acrylic guide

11” x 6” (8” CF) tee

Acrylic vacuum chamber

Glass windows

Poly PMT supports

Inner surface 97% diffuse reflector,covered with TPB wavelength shifter

Neck connects to vacuum andgas/liquid lines

7 kg LAr

DEAP-1 detector

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SAES getter

Ar liquefying chamber

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Fprompt: the discriminator

Yellow: Prompt light regionBlue: Late light region

)s9(TotalPE

)ns150(omptPEPrFprompt

Backgrounds (’s)

Signal (nuclear recoil)

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AmBe (neutron) calibration

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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

Backgrounds

• 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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22Na

e-

e+

511 keV γ

1.274 MeV γ

511 keV γ

Argon

Dark box

Annulus

NaI22Na

Tagged Na-22 setup at Queen’s

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Single PE calibrationGain: ~107

Energy calibration using Na-22Light yield: ~2.8 PE/keV

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Detector stability

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ROI

Tagged Na-22 data

1.53x107 events in energy ROI: (120, 240) PEs, (40, 80) keVee

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Probability of leakage

n

n

r

0

1

rnpromptleak

dr)r(f

dr)r(f)rF(P

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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)

Livetime ~6 hrs Livetime ~10 hrs

x10 reduction

residual backgrounds consistent with radon daughter contamination, now reduced with glove box surface removal

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Radon-222 decay rates

10 decays/m2 of air (surface labs)100 decays/m2 of air (at SNOLAB)

Decay in bulk detector taggedby -particleenergy

LAr

CryostatWall

210Po on surfaceDecay from surfacereleases untagged recoiling nucleus

Daughters from radon decay can be implantedinto surfaces

210-polonium alpha energy = 5.4 MeVEN=103 keVr (sub-micron implantation)

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veto PMTs

H2O shield(7.8 m)

266 8” PMTs

170 cm IDacrylic vessel(3600 kg LAr)

DEAP/CLEAN-3600 detector design

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Acrylic vessel resurfacer for radon removal

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SNOLAB cube hall

SNOLAB Cube Hall

SNO

DEAP-1

DEAP/CLEAN-3600

26MiniCLEANDEAP/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