DEAP-3600 and the Cryopit

Mark Boulay, Queen’s

DEAP-3600 and the Cryopit

Mark BoulayQueen’s University, Kingston

DEAP EAC Meeting August 16, 2011

@

SNOLAB Cube Hall Feb 2010Location of the DEAP-3600 shield tank.


Liquid argon as a dark matter target

• Well-separated singlet and triplet lifetimes in argon allow for good pulse-shape discrimination (PSD) of b/g’s using only scintillation time information, projected to 10-10 at 20 keVee

(see Astroparticle Physics 25, 179 (2006) and arxiv/0904.2930)

• Very large target masses possible, since no absorption of UV

scintillation photons in argon, and no e-drift requirements.

• 1000 kg argon target allows 10-46 cm2 sensitivity (SI) with ~20 keVee threshold, 3-year run

c 40Ar40Ar

c

• Less loss of coherence for lighter nuclei, argon can provide useful information even with relatively high energy threshold

Rate ~ A2F (coherent)


CDMS 2010: 612 kg-days (Ge)XENON100 2011: 1471 kg-days (Xe)DEAP-3600: 1,000,000 kg-days (LAr) background free sensitivity

80 keVr threshold, without depletion of 39Ar

XENON100 arXiv:1104.2549

Plot courtesy of Wolfgang Rau

http://arxiv.org/abs/1104.2549v2


85 cm radius acrylic sphere contains3600 kg LAr (55 cm, 1000 kg fiducial, sealed vacuum vessel to control backgrounds) 266 8” PMTs (warm PMTs to increase light efficiency)

50 cm acrylic light guides and fillers for neutron shielding (from PMTs)

Steel shell for safety to prevent cryogen/water mixing (AV failure)

Only LAr, acrylic, andWLS (10 g) inside of neutronshield

8.5 m diameter water shieldingsized for reduction of (a,n) from rock

DEAP-3600 Detector


DEAP collaborators (Canadian groups)• University of Alberta

D. Grant, P. Gorel, A. Hallin, J. Soukup, C. Ng, B. Beltran, K. Olsen

• Carleton UniversityK. Graham, C. Ouellet

• Queen's UniversityM. Boulay, B. Cai, D. Bearse, K. Dering, M. Chen, S. Florian, R. Gagnon, V.V. Golovko, M. Kuzniak, J.J. Lidgard, A. McDonald, A.J. Noble, E. O’Dwyer, P. Pasuthip, T. Pollman, W. Rau, T. Sonley, P. Skensved, M. Ward

• SNOLAB/LaurentianB. Cleveland, F. Duncan, R. Ford, C.J. Jillings, M. Batygov, E. Vazquez Jauregui

• SNOLABI. Lawson, K. McFarlane, P. Liimatainen, O. Li

• TRIUMFF. Retiere, Alex Muir


DEAP/CLEAN collaborators• University of Alberta: P. Gorel, A. Hallin, J. Soukup, C. Ng, B. Beltran, K. Olsen• Boston University: D. Gastler, E. Kearns• Carleton University: K. Graham, C. Ouellet• Harvard: J. Doyle• Los Alamos National Laboratory: C. Alexander, S.R. Elliott, V. Gehman, V. Guiseppe,

W. Louis, A. Hime, K. Rielage, S. Siebert, J.M. Wouters• MIT: J. Monroe, J. Formaggio• University of New Mexico: F. Giuliani, M. Gold, D. Loomba• NIST Boulder: K. Coakley• University of North Carolina: R. Henning, M. Ronquest • University of Pennsylvania: J. Klein, A. Mastbaum, G. Orebi-Gann• Queen's University: M. Boulay, B. Cai, D. Bearse, K. Dering, M. Chen, S. Florian, R.

Gagnon, V.V. Golovko, M. Kuzniak, J.J. Lidgard, A. McDonald, A.J. Noble, E. O’Dwyer, P. Pasuthip, T. Pollman, W. Rau, T. Sonley, P. Skensved, M. Ward

• SNOLAB/Laurentian: B. Cleveland, F. Duncan, R. Ford, C.J. Jillings, M. Batygov• SNOLAB: I. Lawson, K. McFarlane, P. Liimatainen, O. Li• University of South Dakota: D.-M. Mei• Syracuse University: R. Schnee, M. Kos, B. Wang• TRIUMF: F. Retiere, A. Muir• Yale University: W. Lippincott, D.N. McKinsey, J. Nikkel

CAD groups primarily focused on DEAP-3600US groups: miniCLEAN (includes LNe target, solar neutrino R&D)


Background Raw No. Events in Energy ROI

Fiducial No. Events in Energy ROI

39Ar b’s (natural argon)

1.6x109 <0.2

39Ar b’s (depleted argon)

8.0x107 <0.01

Neutrons 30 <0.2

Surface a’s 150 <0.2

DEAP-3600 Background Budget (3 year run)

Acr+H2O shield

PSD

Resurfacer,reconstruction

Need to resurface inner vessel and ensure purity of TPB and acrylic (40 mm layer, including surface)

Mark Boulay, Queen’sFrom DEAP-STR-2011-009 (Bei Cai)


ET 9390B PMT 5”8” long acrylic guide

11” x 6” (8” CF) tee

Acrylic vacuum chamber

UHV windowspoly PMT supports

inner surface 97% diffuse reflector,Covered with TPB wavelength shifter

Neck connects to vacuum andGas/liquid lines

7 kg LAr

DEAP-1 prototype (7 kg LAr)


R5912 HQE PMTs on DEAP-1 (Feb. 2010) Koby Dering

mineral oil optical coupling identical to DEAP-3600 design


Light yield in DEAP-1 with Hamamatsu R5912 HQE PMTs

>4 pe/keV in DEAP-1

expect higher light yield in DEAP-3600 (greater PMT coverage, 75% vs 20%)

MC simulations (ratio of DEAP-3600 to DEAP-1) show > 6 pe/keV in DEAP-3600, meets design spec.


Calibration of DEAP-1 with AmBe neutron source


β/γ backgrounds

• 39Ar is the most dominant β/γ background

• Expect 109 events in 3 years in (20-40) keVee• Pulse-shape discrimination in DEAP-1

extrapolates to sufficient PSD• Working with Princeton group for 4 tonnes

depleted argon for DEAP-3600 (>50 times depletion)


210Po on surface

Decay in bulk argon taggedby a-particle energy

LAr

a

a

Decay from TPB surface releases untagged recoiling nucleus in argon and a in TPB (see both with low energy)

a Backgrounds in Liquid Argon

TPB

AcrylicPTFE

Decay from TPB surface releases a in argon and recoil nucleus in TPB(see mostly a-particle, high energy)

Decay from inside TPB or acrylic releases a which may also enter LAr.Could see(a) Light from TPB only (prompt) or(b) Light from LAr (range of energies)

DEAP-1 and DEAP-3600 surface profile

both TPB and LAr scintillate


a Backgrounds in LAr (DEAP-1)

210Po

LArTPB

AcrylicPTF

E

232Th chain

238U chain

DEAP-1 data

222Rn+220Rn In DEAP-1: 100 mBq 222Rn 20 mBq 220Rn

Eve

nts/

100

keV

June 2010


Background rates in DEAP-1 (low-energy region 120-240 p.e.)

Date Background Rate (in WIMP ROI)

Configuration Improvements forthis rate

April 2006 20 mBq First run (Queen’s) Careful design with input from materials assays (Ge g couting)

August 2007 7 mBq Water shield (Queen’s) Water shielding, some care in surface exposure (< a few days in lab air)

January 2008 2 mBq Moved to SNOLAB 6000 m.w.e. shielding

August 2008 400 mBq Clean v1 chamber at SNOLAB

Glove box preparation of inner chamber (reduce Rn adsorption/implantation on surfaces)

March 2009 150 mBq Clean v2 chamber at SNOLAB

Sandpaper assay/selection, PTFE instead of BC-620 reflector ,Rn diffusion mitigation, UP water in glove box, documented procedures; Rn Trap.

March 2010 130 mBq Clean v3 chamber at SNOLAB

Acrylic monomer purification for coating chamber. TPB purification.

Feb 2011 ~10 mBq(PRELIMINARY)

Clean v4 chamber at SNOLAB

Inner chamber redesign to remove “Neck Light” events

Mark Boulay, Queen’sChris Jillings – CAP Congress 2011 – Memorial University

Detector Chamber: Gen III

Neutron-like events

Mark Boulay, Queen’sChris Jillings – CAP Congress 2011 – Memorial University

Radon Spike● Used a spike of 222Rn captured from SNOLAB air● Introduced into argon system● Low-energy events in center of detector increased tens

of minutes before high-energy events.● The large peaks at high z-fit did not increase.

Argon inlet


Chris Jillings – CAP Congress 2011 – Memorial University

Detector Chamber: Gen IV, V

Better endcaps

Better plug at neck


Chris Jillings – CAP Congress 2011 – Memorial University

Gen IV Backgrounds


Surface backgrounds in DEAP-1/DEAP-3600

Backgrounds in DEAP-1 dominated by surface events.

Projected sensitivity of 2x10-46 cm2 with DEAP-1 background levels after position reconstruction. (Those are upper limit: near levels of Radon emanation, neutrons in DEAP-1)

(Toy model of fitter response)


DEAP and miniCLEAN shield tanks at SNOLAB


Current Status DEAP-3600

Full capital funding (~10 M$) announced summer 2009, cash flow Nov. 2010

Construction of infrastructure at SNOLAB (support deck and shielding tanks complete, water purification systems, chillers, etc. being installed)

Construction of acrylic vessel at Reynolds Polymer about to begin; will be machined at U of A and installed in Cube Hall. U of A mill upgraded for vessel machining.

20” test vessel has been constructed and bonded at Reynolds Polymer


Current Status DEAP-3600

Several large components ordered/fabricated:

• ultralow-background, highly transparent acrylic (> several m attenuation length) for light guides (Spartech)

August 10 production start• HQE PMTs (first 100 PMTs now in-house at Queen’s being

characterized)• VME digitizing electronics (at TRIUMF)• Large LN2 dewar and 3 KW cryocooler system being fabricated

(Stirling)• Slow controls system in-house at Queen’s

• Argon purification system under development• “Resurfacer” device under development• Continued materials assay and qualification


20” Test Vessel Machining at Alberta


20” Test Vessel at the University of Alberta

Vessel now fully bonded at Reynolds; will be shipped to Queen’s in September for cryogenic/QA testing.




DEAP-3600 Acrylic Vessel Construction/Assembly

Panels are thermoformed and bonded into a spherical shell and neck collar/neck (Reynolds Polymer in Colorado)

Shell is machined (U of A) to include light guide “stubs”

Light guides are bonded on (UG due to transport constraints) onto stubs: Vessel must be rotated to allow bonding of each light guide in approximately horizontal position Full vessel is annealed

Not trivial to scale to significantly larger size!


Acrylic light guide bonding at Alberta


Light guide bonding at U of A

• Developed well-controlled bonding system• Bond parameters are monitored to ensure

consistency• Many test bonds completed, standard LN2 “shock” tests for QA


Future PlansPlan to explore possibility of “scaling-up” single-phase liquid argon, by a factor of ~10

Currently no detailed design or timeline (focus is currently on DEAP-3600). Some considerations: Larger experiment would require depleted argon, and significant storage facility; need to evaluate dominant residual backgrounds in argon after 39Ar (including residuals from muons/spallation)

Safety considerations for large cryogenic target need to be implicit in detector design (especially water shielding/flooding, ODH vent, seismic concerns, and any large dewars)

Experiment much larger than DEAP-3600 should have simplified optical readout (and lower background to reduce requirement for neutron shielding), simplified acrylic vessel (still require “sealed” inner volume for radon reduction), but should be simple to install (perhaps non-structural flat panels?)

Scintillation light readout should in principle be possible at larger scales.


Possible timeline for Cryopit

Current plan is to operate DEAP-3600 and collect some data/gain experience before making decision to seek funding for next scale experiment

Earliest we would consider seeking funding (for detector engineering) is around 2013; still unclear whether larger detector would require Cryopit, but certainly a possibility

Planning some modest feasibility studies in coming year (combination of simulations and evaluating possible designs)


Summary

DEAP-3600 detector under construction in SNOLAB cube hall, target sensitivity is 10-46 cm2

Single-phase liquid argon technology should be scalable to much larger target masses; no detailed technical design study yet completed for DEAP scale-up

Plan to collect initial data with DEAP-3600 before deciding to pursue funding for larger experiment (2013 earliest date to seek funds) Experiment at this scale (likely ~50 M$) would require v. significant collaboration and several funding partners

Larger detector could require Cryopit, significant work to define infrastructure and safety requirements


END

DEAP-3600 and the Cryopit

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