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Mark Boulay SNOLAB V 21/8/06 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 DEAP @ SNOLAB DEAP: Dark Matter Experiment using Argon PSD

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

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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

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

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

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

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

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

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

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

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

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

Mark Boulay SNOLAB V 21/8/06

DEAP-1 (7 kg LAr) at Queen’s

Mark Boulay SNOLAB V 21/8/06

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

PE

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

Mark Boulay SNOLAB V 21/8/06

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

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)

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

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

Mark Boulay SNOLAB V 21/8/06

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

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

Mark Boulay SNOLAB V 21/8/06

DEAP-1 proposed location at SNO

space limits shielding design

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

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)

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

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)