1. The DEAP Experiment Dark Matter Experiment with Argon PSD
Kevin Graham
Queen’s University
M. Boulay, M. Chen, K. Graham, A. Hallin, J. Lidgard, R. Matthew,
A.B. McDonald, K. Nicolics, P. Skensved
Case Western Reserve University
M. Dragowsky
Los Alamos National Laboratory
Hime, D. Mei, K. Rielage, L. Stonehill, J. Wouters
SNOLAB
F. Duncan, I. Lawson
Yale University
D. McKinsey, J. Nikkel

2. Evidence for Dark Matter
lensing gmeasure lens mass from
multiply imaged arcs
measure velocities of galaxies in cluster
measure velocity of gas/stars
vs radius from galactic centre
v2c = G M(r) / r
if light traces mass v should
fall at large radii…but does not
HST Abell 2218
85% of matter is dark matter!
Mihos
NGC 2403

3. Direct Detection of Dark Matter
Cold Dark Matter a WIMPS (can also be LSP!)
predict at the earth:
dark matter energy density 0.3 GeV/cm3
Sun orbiting at 220 km/s
for a given mass and interaction cross-section
estimate c-n scattering rate /kg/year/keV
direct measurement:
look for: elastic scattering of WIMPs
in detector producing nuclear recoils
a low energy and falling keV
ause LAr with PSD
DM signal or improve limit on scattering
cross-section (expect 10’s of events/year) c
40Ar

4. Detection in LAr ionizing radiation forms dimers in LAr
dimers produced in singlet(I1) or triplet(I3) state
singlet state decay time much shorter than triplet
intensity of singlet and triplet states depends on
ionization density along track and hence particle type ns

5. g-like
neutron-like

6. DEAP0 at LANL (Boulay and Hime)
Setup
Goals
~1 kg LAr viewed by single
2” PMT
CsI counter used for tag
calibration with tagged g’s, n’s
22Na: back-to-back 511 keV g’s
AmBe: n and 4.4 MeV g
demonstrate pulse shape
discrimination
determine b/g suppression level
(expect O(108) from MC simulation)
measure I1/I3 for g’s and neutrons
PMT
LAr
CsI tag
Vacuum chamber
windows
source
Digitized
Pulse
Total Charge

7. Deap0 Calibration 22Na 511 keV g AmBe neutron a ~0.1 PE/keV
PromptPE = integral in 250 ns
TotalPE = integral to 10 ms
FPrompt=PromptPE/TotalPE
expect ~0.3 for b/g ~0.8 for n
determine charge/single PE
know peak for 22Na is 511 keV
a ~0.1 PE/keV
(sets sensitivity)
22Na 511 keV g
AmBe neutron
22Na 511 keV g

8. Preliminary Results 22Na AmBe determine fraction of 22Na above 0.7
for PE suppression O(105)
consistent with
background limits
neutrons in region
above 0.7
uncorrected b/g and neutron I1/I3
22Na
AmBe
use background data to determine real and accidental coincidence rate

9. DEAP1 ~10 kg of liquid argon view with 2 - 5” PMT’s
use clean materials and shielding in construction
calibrate detector response at Queen’s
move to SNOLAB early in 2007
measure b/g suppression down to 10 keV threshold
position reconstruction in “z”
at SNOLAB understand background rates/types
can already be competitive within a few
months exposure!
prepare for 1 tonne experiment

10. Neck connects to vacuum and
Gas/liquid lines
Quartz windows
11” x 6” Stainless steel tee
6” acrylic guide
Acrylic vacuum chamber
PMT 5”
inner surface 97% diffuse reflector,
covered with TPB wavelength shifter

11. DEAP1 Constructed! first LAr fill 2 weeks ago response looks good!
begin calibrating next week

12. Backgrounds Type Sources Rate Suppression Method b/g a’s R&D in
U/Th/K
39Ar
106 events/year
clean materials
PSD (108)
clean Ar?
a’s
recoils
ionizing
R&D in
progress
position recon.
PSD
neutron
thermal
fast(a,n)
muon induced
4000 /m2/day
<0.27 /m2/day
shielding
SNOLAB depth

13. DM Sensitivity with LAr with 1-year exposure
LAr with 10 keV (electron) threshold
DEAP1

14. Summary initial proof-of-principle PSD (complete)
calibration of DEAP1 at Queen’s (first fill so far)
aPE/keV, reconstruction, b/n response at 10 keV
calibrate and understand backgrounds at depth
if bkg controlled competitive DM limits soon!
begin design of DEAP3
(1 tonne) experiment!

15. LAr Cryostat wall Decay in bulk detector tagged by a-particle energy
210Po on
surface
Decay in bulk
detector tagged
by a-particle
energy
Decay from
surface releases
untagged
recoiling nucleus
Cryostat
wall
LAr a
Fig 6: Alpha emitters deposited on the detector
surface are a potentially dangerous background.

16. Radon Contamination minimize exposure clean/etch surfaces
210Po on
surface
Decay in bulk
detector tagged
by a-particle
energy
Decay from
surface releases
untagged
recoiling nucleus
Cryostat
wall
LAr a
minimize exposure
clean/etch surfaces
reconstruction suppression

18. Dewar Schematic liquefy purified Argon gas and maintain at 85o K
vacuum chamber
argon line
liquid nitrogen at ~30 PSI
getter

19. CDMS (Cryogenic Dark Matter Search)
g rays
Exploits difference in
deposited charge versus
phonon energy between
b/g ‘s and nuclear recoils
Collection of small detectors
simultaneously measure deposited energy in charge and phonon channels
~1 kg / “tower”
Current best limit
neutrons
(Currently instrumented
5 kg mass)
ZIP detector g Ge
Image from cdms.berkeley.edu

20. Backgrounds
CDMS Collab Meeting 15 Oct 2005

21. Direct detection prediction from SUSY
NMSSM (Next-to-MSSM)
Prediction from talk by
David Cerdeno at SUSY 2005
(JHEP 12 (2004) 048)
10-44 cm2 (10 kg LAr)
10-45 cm2 (100 kg LAr)
maybe within our reach!

22. SNOLAB Excavation Status
DEAP Collab Mtg 10 May 2006

23. Evidence for Dark Matter
clustering of galaxies (LSS)
sensitive to amount of DM
angular power spectrum of CMB
sensitive to baryonic, DM, DE
Virgo Consortium
Add breakdown of matter content here

24. For almost as long as WIMPs have
been around (if they DO exist!)…
U, Th chains are present in
all materials with 109, 1010 y lifetimes
~104decays/kg/year for ppt (1 in 10-12)
impurities
Removing backgrounds to WIMP particle
interactions is the task of DM searchers

25. CDMS (Cryogenic Dark Matter Search)
g rays
Exploits difference in
deposited charge versus
phonon energy between
b/g ‘s and nuclear recoils
Collection of small detectors
simultaneously measure deposited energy in charge and phonon channels
~1 kg / “tower”
Current best limit
neutrons
(Currently instrumented
5 kg mass)
ZIP detector g Ge
Image from cdms.berkeley.edu

26. XENON (proposed experiment)
Total Xe mass 1 tonne
Exploits difference in
ionization signal (electrons)
versus scintillation signal
(photons) between b/g‘s and
nuclear recoils
Figure from Elena Aprile Dark Matter 2004

27. Background rejection with LAr (simulation)
From simulation,
rejection > 108
@ 10 keV
(>>!)
108 simulated e-’s
100 simulated
WIMPs

28. Triplet lifetime check

29. Photomultiplier tube (PMT) backgrounds in DEAP-1
For reference, 250 events/year for the ET9390 PMTs

30. Optimizing optics for DEAP-1
elg = 0.8
epmt = 0.25
a = 0
Y0 = 40 photons/keV
Model incorporating
reflective losses and
absorption:
Y=R[1/S-1] elgepmt(1-a)Y0
Y = yield [photons/keV]
R = surface reflectivity
S = surface PMT coverage
elg = light guiding efficiency
epmt = PMT efficiency
a = absorption
Y0 = photon production yield
Need real model to map inputs to yield,
O(10%) (Kati N.)

31. Dark Matter Candidates
Baryonic Dark Matter - MACHOs
- Brown Dwarfs
Hot Dark Matter - neutrinos
Non-Standard Gravity - MOND
Cold Dark Matter - Axions
- WIMPs
- R-parity conserving supersymmetric models
predict stable LSP (typically neutralino c)
- can have ‘right’ properties for cold dark matter!

32. Evidence for Dark Matter
angular power spectrum of CMB
sensitive to baryons, DM, DE
85% of matter is dark matter!
neutrinos ~few % of matter
WMAP Three Year Results

33. Summary using SNOLAB facility and based on the experience
and success of SNO, there is a unique opportunity
for Canadians to lead experimental research in
- direct search for dark matter
- low-energy solar neutrinos
- neutrinoless double beta decay
SNO+ will have access to most interesting physics
for low-energy solar neutrinos and experiment is built!
DEAP can rapidly evolve from concept to leading edge
dark matter experiment – simple, inexpensive, scalable!

34. Backgrounds expect DM small signal /keV/tonne/day
background suppression crucial
non-nuclear recoil events PSD
nuclear recoil events (shielding, reconstruction)
clean clean clean clean clean!