Transcript Queen`s University
DEAP-3600 and the Cryopit
SNOLAB Cube Hall Feb 2010 Location of the DEAP-3600 shield tank.
@ Mark Boulay , Queen’s Mark Boulay Queen’s University, Kingston DEAP EAC Meeting August 16, 2011
Liquid argon as a dark matter target • Less loss of coherence for lighter nuclei, argon can provide useful information even with relatively high energy threshold 40 Ar c 40 Ar c Rate ~ A 2 F (coherent) •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 keV ee (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
threshold, 3-year run
cm 2
sensitivity (SI) with ~20 keV ee Mark Boulay , Queen’s
Plot courtesy of Wolfgang Rau XENON100 arXiv:1104.2549
80 keVr threshold, without depletion of 39 Ar CDMS 2010: 612 kg-days (Ge) XENON100 2011: 1471 kg-days (Xe) DEAP-3600: 1,000,000 kg-days (LAr) background free sensitivity Mark Boulay , Queen’s
Mark Boulay , Queen’s DEAP-3600 Detector 85 cm radius acrylic sphere contains 3600 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, and WLS (10 g) inside of neutron shield 8.5 m diameter water shielding sized for reduction of ( a ,n) from rock
DEAP collaborators (Canadian groups)
• •
University of Alberta D. Grant
, P. Gorel ,
A. Hallin
, J. Soukup, C. Ng, B. Beltran , K. Olsen
Carleton University
•
K. Graham
, C. Ouellet
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, E. Vazquez Jauregui •
SNOLAB
I. Lawson, K. McFarlane, P. Liimatainen, O. Li •
TRIUMF F. Retiere,
Alex Muir Mark Boulay , Queen’s
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: Harvard: J. Doyle K. Graham
, C. Ouellet
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: SNOLAB: B. Cleveland, F. Duncan
,
R. Ford
I. Lawson, K. McFarlane, P. Liimatainen, O. Li ,
C.J. Jillings,
M. Batygov
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-3600 US groups: miniCLEAN (includes LNe target, solar neutrino R&D) Mark Boulay , Queen’s
DEAP-3600 Background Budget (3 year run)
Background Raw No. Events in Energy ROI Fiducial No. Events in Energy ROI
39 Ar b ’s (natural argon) 39 Ar b ’s (depleted argon) 1.6x10
9 8.0x10
7 <0.2
<0.01
Neutrons 30 <0.2
Surface a ’s 150 <0.2
PSD Acr+H 2 O shield Resurfacer, reconstruction Need to resurface inner vessel and ensure purity of TPB and acrylic (40 m m layer, including surface) Mark Boulay , Queen’s
Mark Boulay , Queen’s From DEAP-STR-2011-009 (Bei Cai)
DEAP-1 prototype (7 kg LAr) UHV windows poly PMT supports Neck connects to vacuum and Gas/liquid lines 11” x 6” (8” CF) tee Mark Boulay , Queen’s 8” long acrylic guide ET 9390B PMT 5” 7 kg LAr Acrylic vacuum chamber inner surface 97% diffuse reflector, Covered with TPB wavelength shifter
R5912 HQE PMTs on DEAP-1 (Feb. 2010) Koby Dering mineral oil optical coupling Mark Boulay , Queen’s identical to DEAP-3600 design
Light yield in DEAP-1 with Hamamatsu R5912 HQE PMTs
Mark Boulay , Queen’s >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
Mark Boulay , Queen’s
β/γ backgrounds •
39
Ar is the most dominant β/γ background • Expect 10
9
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)
Mark Boulay , Queen’s
a B ackgrounds in Liquid Argon a 210 Po on surface a Decay in
bulk argon
tagged by a -particle energy Decay from
TPB surface
releases untagged recoiling nucleus in argon and a in TPB (see both with low energy) Decay from
TPB surface
releases a argon and recoil nucleus in TPB (see mostly a -particle, high energy) in 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)
both TPB and LAr scintillate
Acrylic LAr
a Backgrounds in LAr (DEAP-1) June 2010 232 Th chain 210 Po Acrylic LAr 238 U chain DEAP-1 data Mark Boulay , Queen’s 222 Rn+ 220 Rn In DEAP-1: 100 m Bq 20 m Bq 222 220 Rn Rn
Background rates in DEAP-1 (low-energy region 120-240 p.e.)
Date
April 2006 August 2007 January 2008
Background Rate (in WIMP ROI)
20 mBq 7 mBq 2 mBq
Configuration
First run (Queen’s) Water shield (Queen’s) Moved to SNOLAB
Improvements for this rate
Careful design with input from materials assays (Ge g couting) Water shielding, some care in surface exposure (< a few days in lab air) 6000 m.w.e. shielding August 2008 400 m Bq March 2009 March 2010 Feb 2011 150 m Bq
130
m
Bq ~10
m
Bq (PRELIMINARY) Clean v1 chamber at SNOLAB Clean v2 chamber at SNOLAB Clean v3 chamber at SNOLAB
Glove box preparation of inner chamber (reduce Rn adsorption/implantation on surfaces) Sandpaper assay/selection, PTFE instead of BC-620 reflector ,Rn diffusion mitigation, UP water in glove box, documented procedures; Rn Trap.
Acrylic monomer purification for coating chamber. TPB purification.
Clean v4 chamber at SNOLAB
Inner chamber redesign to remove “Neck Light” events Mark Boulay , Queen’s
Detector Chamber: Gen III
Neutron-like events Mark Boulay , Queen’s Chris Jillings – CAP Congress 2011 – Memorial University
Radon Spike
●
Used a spike of
222
Rn 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 Mark Boulay , Queen’s Chris Jillings – CAP Congress 2011 – Memorial University
Detector Chamber: Gen IV, V
Better plug at neck Better endcaps Mark Boulay , Queen’s Chris Jillings – CAP Congress 2011 – Memorial University
Gen IV Backgrounds
Mark Boulay , Queen’s Chris Jillings – CAP Congress 2011 – Memorial University
Surface backgrounds in DEAP-1/DEAP-3600
(Toy model of fitter response) Backgrounds in DEAP-1 dominated by surface events.
Projected sensitivity of 2x10 -46 cm 2 with DEAP-1 background levels after position reconstruction.
(Those are upper limit: near levels of Radon emanation, neutrons in DEAP-1) Mark Boulay , Queen’s
DEAP and miniCLEAN shield tanks at SNOLAB
Mark Boulay , Queen’s
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 Mark Boulay , Queen’s
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 Mark Boulay , Queen’s
20” Test Vessel Machining at Alberta
Mark Boulay , Queen’s
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.
Mark Boulay , Queen’s
Mark Boulay , Queen’s
Mark Boulay , Queen’s
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!
Mark Boulay , Queen’s
Acrylic light guide bonding at Alberta
Mark Boulay , Queen’s
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 Mark Boulay , Queen’s
Future Plans
Plan 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.
Mark Boulay , Queen’s
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) Mark Boulay , Queen’s
Summary DEAP-3600 detector under construction in SNOLAB cube hall, target sensitivity is 10 -46 cm 2 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 Mark Boulay , Queen’s
END Mark Boulay , Queen’s