1. Cryogenic Dark Matter Search
Results from the
Cryogenic Dark Matter Search
Wolfgang Rau
On behalf of the CDMS collaboration

2. CDMS Collaboration CDMS resutls – W. Rau - SNOLAB Workshop 2010
California Institute of Technology Z. Ahmed, J. Filippini, S.R. Golwala, D. Moore
Case Western Reserve University D. Akerib, C.N. Bailey, M.R. Dragowsky, D.R. Grant, R. Hennings-Yeomans
Fermi National Accelerator Laboratory D. A. Bauer, F. DeJongh, J. Hall, D. Holmgren, L. Hsu, E. Ramberg, R.L. Schmitt, J. Yoo
Massachusetts Institute of Technology E. Figueroa-Feliciano, S. Hertel, S.W. Leman, K.A. McCarthy, P. Wikus
NIST * K. Irwin
Queen’s University C. Crewdson *, P. Di Stefano *, J. Fox *, S. Liu *, C. Martinez *, P. Nadeau *, W. Rau
Santa Clara University B. A. Young
SLAC/KIPAC * M. Asai, A. Borgland, D. Brandt, W. Craddock, E. do Couto e Silva, G.G. Godrey, J. Hasi, M. Kelsey, C. J. Kenney, P. C. Kim, R. Partridge, R. Resch, J.G. Weisend, D. Wright
Southern Methodist University J. Cooley
Stanford University P.L. Brink, B. Cabrera, M. Cherry *, R. Moffatt*, L. Novak, R.W. Ogburn , M. Pyle, M. Razeti*, B. Shank*, A. Tomada, S. Yellin, J. Yen*
Syracuse University M. Kos, M. Kiveni, R. W. Schnee
Texas A&M K. Koch*, R. Mahapatra, M. Platt *, K. Prasad*, J. Snader
University of California, Berkeley M. Daal, T. Doughty* , N. Mirabolfathi, A. Phipps, B. Sadoulet, D. Seitz, B. Serfass, D. Speller*, K.M. Sundqvist
University of California, Santa Barbara R. Bunker, D.O. Caldwell, H. Nelson
University of Colorado Denver B.A. Hines, M.E. Huber
University of Florida T. Saab, D. Balakishiyeva, B. Welliver *
University of Minnesota H. Chagani*, J. Beaty, P. Cushman, S. Fallows, M. Fritts, T. Hoffer*, O. Kamaev, V. Mandic, X. Qiu, R. Radpour*, A. Reisetter, A. Villano*, J. Zhang
University of Zurich S. Arrenberg, T. Bruch, L. Baudis, M. Tarka
* new collaborators or new institutions in SuperCDMS

3. Overview Introduction – Dark Matter CDMS technology
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Overview
Introduction – Dark Matter
CDMS technology
Data Analysis and WIMP Results
Other Results (time permitting)

4. Introduction – Dark Matter
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Introduction – Dark Matter
Coma Cluster
Zwicky, 1930s
Coma cluster
Dark
Matter
CDMS
Technology
Strong and multiple observational evidence for dark matter
Weakly Interacting Massive Particles (WIMPs) are among the best motivated candidates.
Vera Rubin-Cooper,
Rotation curves
1970s
Analysis
Results
Other
Analyses
Abell 2218 (HST)
Gravitational Lensing
Bullet Cluster
Conclusion
WMAP

5. Ionization energy [keV eeq]
CDMS resutls – W. Rau - SNOLAB Workshop 2010
CDMS Technology
Operating Principle
Phonon signal: measures energy deposition
Ionization signal: distinguishes between electron (large) and nuclear recoils (small)
Surface events have reduced ionization: need additional information to identify
Thermal coupling
Thermal
bath
Dark
Matter
Evidence
Phonon sensor + -
Target
CDMS
Technology e n
Analysis
Results
Other
Analyses
Ionization energy [keV eeq]
Phonon signal
Electron recoils
from β’s and γ’s
Conclusion
Electron recoil
Nuclear recoil
Charge signal
Nuclear recoils
from neutrons
Phonon energy [keV]

6. CDMS Technology Detectors Cryogenic ionization detectors, Ge (Si)
CDMS resutls – W. Rau - SNOLAB Workshop 2010
CDMS Technology
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
Dark
Matter
Evidence
CDMS
Technology
Analysis
Results
Other
Analyses
Conclusion

7. CDMS Technology Surface effect + E Detector Performance Detector
CDMS resutls – W. Rau - SNOLAB Workshop 2010
CDMS Technology
Detector Performance
Detector
Collimator
Dark
Matter
g-band
n-band
Evidence
CDMS
Technology
Ionization/Recoil energy
b-band
Analysis
Results
Recoil energy [keV]
Other
Analyses gs
neutrons bs
surface event
nuclear recoil
rising edge slope
Surface effect
Conclusion + + – + – E
Reduced charge signal but faster phonon signal

8. CDMS Technology Experimental Setup „Tower“ Soudan (6 Detectors)
CDMS resutls – W. Rau - SNOLAB Workshop 2010
CDMS Technology
Experimental Setup
„Tower“
(6 Detectors)
Soudan
Underground lab
(2000 m w.e.)
Dark
Matter
Evidence
CDMS
Technology
Analysis
Results
Cryostat, Coldbox
Shielding
Other
Analyses
Conclusion
5 Towers (~ 5 kg Ge ) operated 2006 – 2008

9. Data Analysis Event Reconstruction Event reconstruction
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Event Reconstruction
Event reconstruction
For each trigger ALL detectors are read out, including muon-veto
Optimal Filter (phonon pulse shape varying, so not really ‘optimal’, but gives best resolution)
Extract basic parameters (Amplitude, Event time)
Multi-parameter pulse fit
Events time-stamped to correlate with slow control parameters / Minos neutrino beam
Dark
Matter
Evidence
Time bins [0.8 s]
Amplitude [a.u.]
CDMS
Technology
Analysis
Results
Other
Analyses
Conclusion

10. Data Analysis Data Quality Kolmogorov-Smirnov test
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Data Quality
Kolmogorov-Smirnov test
Pick a few ‘golden’ data sets
Compare parameter distributions
Dark
Matter
Evidence
Example
Detector neutralization / low yield events
CDMS
Technology
Charge carriers trapped at defects  build up counter field  poor charge collections
 increase background
datasets
templates
Analysis
Results
Fraction of low yield events
Date
Other
Analyses
average
5 above average
(colored points = poorly neutralized datasets)
Conclusion

11. Data Analysis Data Quantity Total raw exposure is 612 kg-days
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Data Quantity
Dark
Matter
Evidence
recorded data
Total raw exposure is 612 kg-days
CDMS
Technology
some detectors not analyzed for WIMP scatters
Analysis
Results
raw exposure
periods of poor data quality removed
Other
Analyses
this work
Conclusion
2008 published data

12. Data Analysis Position Dependent Calibration
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Position Dependent Calibration
Large area sensor not completely homogeneous
Use extensive  calibration to create lookup table for position dependent pulse height/timing distributions
Compare each event from WIMP search data with  events at same location
Position determination not perfect: ambiguity close to edge of detector where timing distributions are changing quickly
May lead to miscalibration
Dark
Matter
Position Dependence of Timing Parameter (measured with e-recoils)
Evidence
CDMS
Technology
events near and outside fiducial volume
Analysis
Results
Radius from arrival time
Timing parameter
increasing radius
Other
Analyses
Conclusion
Radius from energy partition
Improvement in this analysis
Include s outside fiducial volume in lookup table
 reduces timing outliers from miscalibration

13. Background Estimate – Neutrons
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Background Estimate – Neutrons
Dark
Matter
Radiogenic Neutrons
From rock
negligible (neutron shield!)
From experimental setup
estimated from screening measurements,  BG analysis
Main contributions from spontaneous fission of U in Cu/Pb
Caveat: cannot measure U with  screening, only daughters – ICPMS measurement for EXO (Pb from same source) indicate lower contamination
Total 0.03 – 0.06 events expected
Cosmogenic Neutrons
Muons in experimental setup; internal
negligible (muon veto detector)
Muons in surrounding rock; external
Use Monte Carlo to estimate rate
Compare MC for n from vetoed (internal) muons to measured rate
Scale MC result for external muons by ‘measured/MC’ ratio for internal muons
Expected rate: (stat)
Evidence
CDMS
Technology
Analysis
Results
Other
Analyses
Conclusion
+ 0.04
– 0.03

14. Data Analysis Background Estimate – Surface Events, ‘Leakage’
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Background Estimate – Surface Events, ‘Leakage’
Dark
Matter
Timing Distribution – Surface vs. Neutrons
Evidence
CDMS
Technology
Analysis
Results
Nuclear recoils from Cf neutron source
Other
Analyses
Surface events from Ba calibration
Conclusion
Tail distribution different for each detector determines cut position

15. Data Analysis Background Estimate – Surface Events, ‘Leakage’
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Background Estimate – Surface Events, ‘Leakage’
Look at surface events outside signal region (‘sideband’)
Count events passing / failing cut – extrapolate to signal region
Dark
Matter
Evidence
Sideband 1
Multiple-scatters in NR band
Sideband 2
Singles and multiples just outside NR band
Sideband 3
Singles and multiples Ba calibration in wide region
CDMS
Technology
Correct for systematic effects due to different distributions in energy and yield
Analysis
Results
WIMP Search Data
133Ba
252Cf
Other
Analyses
Conclusion
Leakage estimate = x # signal region, failing
# sideband, passing
# sideband, failing
Estimates consistent; total expected leakage from ‘blind’ data: 0.6  0.1

16. Data Analysis Expected Sensitivity
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Expected Sensitivity
Dark
Matter
Evidence
CDMS
Technology
Analysis
Results
Other
Analyses
Conclusion

17. Data Analysis Unblinding signal region Failing Cut ( Surface events)
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Unblinding
Dark
Matter
Evidence
masked signal region (2 NR band)
CDMS
Technology
2 events near NR band
Event 1:
Tower 1, ZIP 5 (T1Z5)
Sat. Oct. 27, 2007
8:48pm CDT
Analysis
Results
signal region
Other
Analyses
Conclusion
Event 2:
Tower 3, ZIP 4 (T3Z4)
Sun. Aug. 5, 2007
2:41 pm CDT
Failing Cut ( Surface events)
Passing Cut ( Good events)

18. Post-unblinding Studies – Data Quality Recheck
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Post-unblinding Studies – Data Quality Recheck
Dark
Matter
Evidence
CDMS
Technology
Analysis
Results
Other
Analyses
Conclusion
Everything seems to have been in best order

19. pulse height (ADC units)
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Post-unblinding Studies – Event Reconstruction
Could there be a problem with the start time of the charge pulse?
Closeup of template fit to ionization pulse for event 2
[ADC bin]
pulse height (ADC units)
Dark
Matter
Evidence
CDMS
Technology
fitted start time
What is the true start time?
2 of the fit
template start time [ADC bin]
Analysis
Results
Other
Analyses
affects only ~1% of events with <6 keV ionization energy
mostly accounted for in the pre-unblinding leakage estimate. ~
Conclusion
A more careful accounting revised the surface event leakage estimate from 0.6 to 0.8 events

20. Data Analysis Cut Variation and Probabilities
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Cut Variation and Probabilities
Dark
Matter
Evidence
Tightening cut to ~1/2 expected leakage would remove both events
Would cost 26 % of exposure
Loosening cut to ~2 expected leakage would add one more event
Limit not very sensitive to cut position
CDMS
Technology
Analysis
Results
Other
Analyses
1.0 10
estimated surface event leakage from 133Ba
Conclusion
Probability to see 2 or more events from surface event leakage: ~20 %
Probability to see 2 or more events from background including neutrons: ~23 %
These values indicate that the results of this analysis cannot be interpreted as significant evidence for WIMP interactions, but we cannot reject either event as signal.

21. Data Analysis Likelihood analysis
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Likelihood analysis
Determine how well the event distribution fits surface event hypothesis
Compare to how well it fits nuclear recoil hypothesis
Conclusion: either might be possible
Dark
Matter
Evidence
CDMS
Technology
Analysis
Results
Other
Analyses
Nuclear recoils from Cf neutron source
Conclusion
Surface events from Ba calibration

22. Data Analysis Limits Minimum @ ~70 GeV CDMS new 7.0  10-8 pb
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Limits
Dark
Matter
Evidence
CRESST 08
CDMS
Technology
CDMS (08)
CDMS, new
CDMS, total
XENON 10
Expected sensitivity
WARP
Analysis
Results
EDELWEISS (09)
ZEPLIN III
Other
Analyses
Conclusion
~70 GeV
CDMS new 7.0  10-8 pb
CDMS combined 3.8  10-8 pb

23. Spin Dependent Interaction
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Spin Dependent Interaction
PICASSO, COUPP, XENON
Dark
Matter
Evidence
CRESST I
CDMS (n)
XENON (n)
XENON (p)
KIMS (p)
CDMS (p)
KIMS (n)
Interaction may depend on spin of target
May also depend on spin carrying nucleon (p or n)
DAMA could avoid conflict with CDMS and XENON
COUPP and PICASSO exclude most of the DAMA region
If nucleon type is ignored, XENON provides strong limit
COUPP (p)
CDMS
Technology
COUPP, 4 kg (p, prelim 2010)
PICASSO (p)
DAMA (p)
Analysis
Results
SuperKamiokande (p)
Other
Analyses
IceCube (p)
Conclusion

24. Data Analysis Inelastic Dark Matter
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Data Analysis
Inelastic Dark Matter
Dark
Matter
Evidence
Proposed by Wiener et al. could explain DAMA/LIBRA
Scattering includes transition of WIMP to excited state ( E= )
DAMA allowed: marginalized over cross section
Hashed: excluded at 90 % C.L.
New (preliminary) results from CRESST: all DAMA allowed region excluded
CDMS
Technology
Analysis
Results
Other
Analyses
Conclusion

25. CoGeNT – Evidence for Dark Matter?
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Other Results
CoGeNT – Evidence for Dark Matter?
Low threshold high resolution Ge detector
Ultra low background
No discrimination
Observe rise in spectrum at low energy
2/dof for ‘no WIMP’ hypothesis: 20.4/20
Claim that fit with WIMPs is better (give example for fit with 2/dof = 20.1/18)
Show preferred region
Tension with CDMS Si data (PhD thesis by J. Filippini, no paper published yet)
Dark
Matter
Evidence
CDMS
Technology
Preliminary!!
Analysis
Results
Other
Analyses
Conclusion

26. XENON100 – Preliminary Limit
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Other Results
XENON100 – Preliminary Limit
Dark
Matter
Evidence
CRESST 08
CDMS
Technology
CDMS (08)
XENON 100
CDMS, new
CDMS, total
XENON 10
WARP
Analysis
Results
EDELWEISS (09)
ZEPLIN III
Other
Analyses
Conclusion

27. Other Analyses Axions Solar Axions
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Other Analyses
Axions
Solar Axions
Convert in nuclear electric field to 
“Bragg” condition enhances x-section
Dark
Matter
Evidence
CDMS
Technology
Analysis
Results
Other
Analyses
Conclusion

28. Low Energy Electron Recoils Spectrum
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Other Analyses
Low Energy Electron Recoils Spectrum
No excess above background!
Interpretation with respect to relic axions:
Signal: peak at axion mass
No preferred direction
Consider all electron recoil events
Dark
Matter
Evidence
CDMS
Technology
Analysis
Results
Other
Analyses
Conclusion

29. Ongoing Analyses Low Energy Threshold
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Ongoing Analyses
Low Energy Threshold
Dark
Matter
Evidence
Expand energy range down to O(1 keV) No ER vs NR discrimination  will have background, but expected rate increases strongly at low energy (low mass WIMPs)
Dedicated ultra-low threshold experiment employ Neganov-Luke effect (thermal signal amplification from drifting charges)
Finalise Si analysis
CDMS
Technology
Analysis
Results
Other
Analyses
Conclusion

30. CDMS resutls – W. Rau - SNOLAB Workshop 2010
Conclusion
Dark
Matter
CDMS
Technology
We present the analysis of new data comprising 612 kgd raw exposure
Expected background is 0.8 from surface events and <0.1 from neutrons
We observe 2 events
This result is statistically compatible with expected background (23 % prob), so they do not constitute statistically significant signal
Both events are compatible with being nuclear recoils or surface event background
Other analyses: solar axions, low energy ER, low threshold WIMP analysis
Analysis
Results
Other
Analyses
Conclusion

31. Fine CDMS resutls – W. Rau - SNOLAB Workshop 2010 Cryogenic Evidence
Super-
heated
Scintillator
Directional
Conclusion