w. rausnolab workshop 2009 s u p e r c d m s wolfgang rau queen’s university cdms technology...
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W. Rau SNOLAB workshop 2009
S u p e r C D M SWolfgang Rau
Queen’s University
CDMS TechnologyAnalysis and Results
SuperCDMSDetector R&D
Underground TFRoadmap
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W. Rau SNOLAB workshop 2009 2
SuperCDMS Collaboration
Caltech Z. Ahmed, J. Filippini, S. R. Golwala, D. Moore, R. W. OgburnFermilab D. A. Bauer, F. DeJongh J. Hall, L. Hsu, D. Holmgren, E. Ramberg, J. YooMIT E. Figueroa-Feliciano, S. Hertel, S. Leman, K. McCarthy, P. WikusNIST K. IrwinQueen’s University N. Fatemighomi, J. Fox, S. Liu, W. Rau, Santa Clara University B. A. YoungSLAC E. do Couto e Silva, G. GodfreyStanford University P.L. Brink, B. Cabrera, M. Pyle, S. YellinSouthern Methodist U J. CooleySyracuse University R.W. Schnee, M. Kos, J. M. KiveniTexas A&M R. Mahapatra, M. Platt, M. VanDyke, J. EricksonUC Berkeley M. Daal, N. Mirabolfathi, B. Sadoulet, D. Seitz, B. Serfass, K. SundqvistUC Santa Barbara R. Bunker, D. O. Caldwell, H. Nelson, J. SandersU of Colorado at Denver M. E. HuberU of Florida T. Saab, D. BalakishiyevaU of Minnesota P. Cushman, M. Fritts, V. Mandic, X. Qiu, O. Kamaev, A. ReisetterU of Zürich S. Arrenberg, T. Bruch, L. Baudis, M. Tarka
P. Di Stefano
W. Rau SNOLAB workshop 2009
CDMS Technology
Thermal couplingThermalbath
Phonon sensor
Target
+++ +
-- --
++
+ +
-- - - -
- -
++ +en
Recoil energy [keV]
Ioni
zatio
n si
gnal
[keV
eeq
]
Nuclear recoilsfrom neutrons
Nuclear recoilsfrom neutrons
Electron recoilsfrom β’s and γ’sElectron recoilsfrom β’s and γ’s
• Measure energy deposit through thermal energy, requires low temperature
• Electron recoil (ER) events produce more electron-hole pairs in semiconductor than nuclear recoils (NR) events do
• Measure charge signal to discriminate between signal (NR) and background (ER)
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Operation Principle
W. Rau SNOLAB workshop 2009
CDMS TechnologyCDMS Detectors• Cryogenic ionization detectors, Ge (Si) = 7 cm, h = 1 cm, m = 250 g (100 g)• Thermal readout: superconducting phase
transition sensor (TES)• Transition temperature: 50 – 100 mK• 4 sensors/detector, fast signal (< ms)• Charge readout: Al electrode, divided
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W. Rau SNOLAB workshop 2009
CDMS TechnologyIo
nisa
tion/
Reco
il En
ergi
e
Recoil Energie [keV]
++
+
+
––––
E++++
–– ––
+
Surface Effect
-Band
-Band
n-Band’s
neutrons
’s
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Surface events
W. Rau SNOLAB workshop 2009
CDMS Technology
5 Towers: ~5 kg Ge, 1 kg Si
Operated in Soudan Lab (Minnesota) 2006 – 2009
Stack of 6 detectors
“Tower”
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CDMS Setup
W. Rau SNOLAB workshop 2009
Analysis and ResultsPublished Data:• Data from Oct. 2006 – June 2007• Raw exposure: ~ 400 kg days• Analysis threshold: 10 keV• Main analysis steps:
- Cover signal region- Remove periods with bad
detector performance- Determine position
dependent calibration and timing performance
- Remove multiple scatter & muon veto events
- Remove surface events (timing)120 kg days after cuts- Calculate expected background0.6 0.5 events expected- Open the box
• NO events observed!
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W. Rau SNOLAB workshop 2009
Analysis and Results
CDMS, Ge
CDMS, Si
EDELWEISS
XENON 10CDMS, GeCombined Soudan Data
CRESST
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WIMP Limits
W. Rau SNOLAB workshop 2009
Analysis and Results
Presently under analysis
• Data from July 2007 – fall 2008• Increase of total exposure by a factor of ~3• Improvements in data analysis:
- Data quality cuts- Better algorithm to account for position dependence- Will need to tighten surface event cuts (timing) to keep
expected background to < 1 event- Test new approaches for timing analysis
• Timeline: announce results this fall• Expected improvement in sensitivity:
factor 2-3 (similar to increase in exposure)
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W. Rau SNOLAB workshop 2009
Analysis and Results
Example of Improvements (calibration data)•Tighter NR yield band•Fewer outliers in timing distribution
Old New
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W. Rau SNOLAB workshop 2009
SuperCDMS
Larger detectors (250 g 630 g)
Improved sensor design
Tower SuperTowerMore active detectors per tower:
4 out of 6 5 out of 7 (~ 1 kg 3 kg)
Short term goal:Build and install 5 SuperTowers(first installed/cold)
Medium term goal:Further increase mass/module; build 100-200 kg experiment
Long term: ~ 1 ton11
W. Rau SNOLAB workshop 2009
SuperCDMS
Detector performance (test facility data)•Phonon energy resolution: similar to old detectors (in spite of 2.5 x mass)•Timing: faster due to larger Al coverage•Surface event discrimination: similar to old detectorsDifficult to estimate due to neutron background at testing facility
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W. Rau SNOLAB workshop 2009
SuperCDMS
First peek at SuperCDMS data
Determine alpha rate (indicator for expected surface beta background)•In fiducial volume: below target (0.4/detector/day)•Outside: rate scales as expected with area of side walls
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W. Rau SNOLAB workshop 2009
Shileding [mwe]
log
(Muo
n flu
x [m
-2s-1
])
Need to reduce background!•Reduce surface contamination (Rn, volume/surface ratio)•Improve discrimination•Build new, cleaner setup•Reduce cosmic ray background by moving deeper Move to SNOLAB
SuperCDMS
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SuperCDMS Sensitivity
W. Rau SNOLAB workshop 2009
Detector R&DInterleaved electrodes:
Electric field calculation
Electrode/sensor layout
Individual TES
Phonon sensors on top and bottom
i Z I P
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W. Rau SNOLAB workshop 2009
Detector R&DFirst iZIP data
Excellent basic performance:•Phonon energy resolution: << 1 keV•Yield based discrimination: 1/3000(considerably better than present detectors)
• Charge based discrimination: 1/1000• Additional discrimination from phonon
signal timing and energy distribution between top and bottom
Discrimination study limited by neutron background in (surface) lab.
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Surface charge signal
Bulk
cha
rge
sign
al
Recoil energy [keV]
Ioni
zatio
n yi
eld
W. Rau SNOLAB workshop 2009
Underground TF
Therefore we would like to investigating the option of setting up anUnderground detector Testing Facility at SNOLAB
• Discrimination power required for 100 kg scale (or larger) experiments cannot be tested above ground (accidental neutron interaction rate too high)
• Detector modules larger than present SuperCDMS detectors are desirable but cannot be tested above ground (pile-up)
• Background from contamination of detectors cannot be measured above ground
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Mostly neutron background
Motivation
Recoil energy [keV]
Ioni
zatio
n yi
eld
W. Rau SNOLAB workshop 2009
Underground TF
• Cryostat available at no (or low) cost (to be equipped with He re-liquefier)• Need to design shielding (water tank?) against environmental neutrons / gammas• Space: could be located in ladder lab without major impact on SuperCDMS setup
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What would we need?
Poly Lid
Cryo
stat
Wat
er
shie
ld
Crane
W. Rau SNOLAB workshop 2009
Underground TF
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Request from SNOLAB (first guess)
Installation• Support for lab interface (crane, electrical power, cooling water etc.)• Engineering support (SNOLAB specific design considerations)• Technical support during installation• Temporary space in surface building to test cryostat before moving UG• Transport of components to underground lab
Operation• Electrical power consumption: ~ 10 kW• Cooling water (~2 tons of cooling power)• Occasionally: liquid cryogenics (LN/LHe)• Some tech support
First draft LoI available
W. Rau SNOLAB workshop 2009
Roadmap
Short Term: SuperCDMS @ Soudan-1 SuperTower operational-2nd ST under preparation-ST 3-5: to be deployed during 2010-Operation until summer 2012
Medium Term: SuperCDMS @ SNOLAB-CFI proposal for infrastructure not funded-Will apply again next year-Funding anticipated in FY 2011
Long Term: ton scale Ge dark matter experiment-R&D towards larger detector modules (up to 6” diameter)-Investigate feasibility of using lower grade Ge (to reduce cost per mass)-Work with Ge crystal producers to optimize production for our needs-Streamlining of detector production (improve production yield, reduce testing effort)-Investigate alternative sensor designs and readout schemes (multiplexing)
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W. Rau SNOLAB workshop 2009
Conclusions
• CDMS continues to provide the most sensitive WIMP-nucleon cross section limits(WIMP masses above ~ 45 GeV and spin independent coherent interaction)
• Factor 2-3 improvement expected very soon (data presently under analysis)• SuperCDMS started! First SuperTower is operational
• Detector R&D: excellent performance for iZIP• Need Underground TF to demonstrate discrimination/performance of new detectors
(iZIP, large substrates, …) for experiment with >100 kg target• Ask for comments from EAC wrt space allocation and support from SNOLAB
(lab interface, engineering, technical support) for Underground TF
• 5 ST @ Soudan to be deployed in 2010• SuperCDMS @ SNOLAB: 100-200 kg
Delayed by funding agencies (funding anticipated for FY 2011)• R&D towards ton scale Ge DM experiment
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