S u p e r C D M S Wolfgang Rau Queen’s University

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


CDMS Technology

Thermal couplingThermalbath

Phonon sensor

Target

+++ +

-- --

++

+ +

-- - - -

- -

++ +en

Recoil energy [keV]

Ioni

zatio

n sig

nal [

keV

eeq]

Nuclear recoilsfrom neutrons

Electron 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


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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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


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


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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Analysis and Results

CDMS, Ge

CDMS, Si

EDELWEISS

XENON 10 CDMS, GeCombined Soudan Data

CRESST

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WIMP Limits



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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Example of Improvements (calibration data)•Tighter NR yield band•Fewer outliers in timing distribution

Old New

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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


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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SuperCDMS

First peek at SuperCDMS dataDetermine 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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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


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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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

signa

l

Recoil energy [keV]

Ioni

zatio

n yi

eld


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


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


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


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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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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S u p e r C D M S Wolfgang Rau Queen’s University

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