results from the cryogenic dark matter search
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Results from the Cryogenic Dark Matter Search. Wolfgang Rau On behalf of the CDMS collaboration. CDMS Collaboration. California Institute of Technology Z. Ahmed, J. Filippini , S.R. Golwala , D. Moore - PowerPoint PPT PresentationTRANSCRIPT
Results from theCryogenic Dark Matter Search
Wolfgang Rau
On behalf of the CDMS collaboration
CDMS Collaboration
California Institute of TechnologyZ. Ahmed, J. Filippini, S.R. Golwala, D. Moore
Case Western Reserve UniversityD. Akerib, C.N. Bailey, M.R. Dragowsky, D.R. Grant, R. Hennings-Yeomans
Fermi National Accelerator LaboratoryD. A. Bauer, F. DeJongh, J. Hall, D. Holmgren, L. Hsu, E. Ramberg, R.L. Schmitt, J. Yoo
Massachusetts Institute of TechnologyE. Figueroa-Feliciano, S. Hertel, S.W. Leman, K.A. McCarthy, P. Wikus
NIST *K. Irwin
Queen’s UniversityC. Crewdson *, P. Di Stefano *, J. Fox *, S. Liu *, C. Martinez *, P. Nadeau *, W. Rau
Santa Clara UniversityB. 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 UniversityJ. 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 UniversityM. Kos, M. Kiveni, R. W. Schnee
Texas A&MK. 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 BarbaraR. Bunker, D.O. Caldwell, H. Nelson
University of Colorado DenverB.A. Hines, M.E. Huber
University of FloridaT. 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 ZurichS. Arrenberg, T. Bruch, L. Baudis, M. Tarka* new collaborators or new institutions in SuperCDMS
CDMS resutls – W. Rau - SNOLAB Workshop 2010
• Introduction – Dark Matter• CDMS technology• Data Analysis and WIMP Results • Other Results (time permitting)
OverviewCDMS resutls – W. Rau - SNOLAB Workshop 2010
4Analysis
Results
ConclusionCDM
S Technology
Dark M
atter
WMAP
Other
AnalysesIntroduction – Dark Matter
Coma Cluster
Vera Rubin-Cooper, Rotation curves1970s
Abell 2218 (HST)
Gravitational LensingBullet Cluster
Zwicky, 1930s Coma cluster
• Strong and multiple observational
evidence for dark matter
• Weakly Interacting Massive
Particles (WIMPs) are among the
best motivated candidates.
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5
EvidenceAnalysis
Results
Conclusion
CDMS TechnologyOperating Principle
CDMS
TechnologyDark M
atterO
ther Analyses
Thermal couplingThermalbath
Phonon sensor
Target
+++ +
-- --
++
+ +
-- - - -
- -
++ +en
Phonon energy [keV]
Ioni
zatio
n en
ergy
[keV
eeq
]
Nuclear recoilsfrom neutrons
Electron recoilsfrom β’s and γ’s
• 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
Phon
on si
gnal
Char
ge si
gnal
Electron recoil Nuclear recoil
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EvidenceAnalysis
Results
Conclusion
CDMS TechnologyDetectors
CDMS
TechnologyDark M
atterO
ther Analyses
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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EvidenceAnalysis
Results
ConclusionCDM
S Technology
Dark M
atterO
ther Analyses
CDMS TechnologyDetector Performance
Detector
Ioni
zatio
n/Re
coil
ener
gy
Recoil energy [keV]
Collimator
++
+
+
––––
E++++
–– ––+
Surface effect
b-band
g-band
n-band
gs
neutrons
bs
Reduced charge signalbut faster phonon signal
surface event
nuclear recoil
rising edge slope
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EvidenceAnalysis
Results
ConclusionCDM
S Technology
Dark M
atterO
ther Analyses
CDMS TechnologyExperimental Setup
„Tower“(6 Detectors)
Cryostat, ColdboxShielding
SoudanUnderground lab(2000 m w.e.)
5 Towers (~ 5 kg Ge ) operated 2006 – 2008
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EvidenceCDM
S Technology
AnalysisResu
lts
ConclusionDark M
atterO
ther Analyses
Data AnalysisEvent Reconstruction
Time bins [0.8 s]
Ampl
itude
[a.u
.]
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
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10
EvidenceCDM
S Technology
AnalysisResu
lts
ConclusionDark M
atterO
ther Analyses
Data AnalysisData Quality
Frac
tion
of lo
w y
ield
eve
nts
Dateda
tase
ts
templates
ExampleDetector neutralization / low yield events
Kolmogorov-Smirnov test• Pick a few ‘golden’ data sets• Compare parameter
distributions
average5 above average(colored points = poorly neutralized datasets)
Charge carriers trapped at defects build up counter field poor charge collections increase background
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EvidenceCDM
S Technology
AnalysisResu
lts
ConclusionDark M
atterO
ther Analyses
Data AnalysisData Quantity
raw exposure
Total raw exposure is 612 kg-days
this work
2008 published data
some detectors not analyzed for WIMP scatters
periods of poor data quality
removed
recorded data
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EvidenceCDM
S Technology
AnalysisResu
lts
ConclusionDark M
atterO
ther Analyses
Data AnalysisPosition Dependent Calibration
Timing param
eter
Position Dependence of Timing Parameter (measured with e-recoils)
events near and outside fiducial volume
increasi
ng radius
Radi
us fr
om a
rriv
al ti
me
Radius from energy partition
• Large area sensor not completely homogeneous
• Use extensive g calibration to create lookup table for position dependent pulse height/timing distributions
• Compare each event from WIMP search data with g events at same location
• Position determination not perfect: ambiguity close to edge of detector where timing distributions are changing quickly
• May lead to miscalibrationImprovement in this analysis Include gs outside fiducial volume in lookup table reduces timing outliers from miscalibration
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EvidenceCDM
S Technology
AnalysisResu
lts
ConclusionDark M
atterO
ther Analyses
Data AnalysisBackground Estimate – Neutrons
Radiogenic NeutronsFrom rock
negligible (neutron shield!)From experimental setup • estimated from screening
measurements, g BG analysis• Main contributions from
spontaneous fission of U in Cu/Pb• Caveat: cannot measure U with g
screening, only daughters – ICPMS measurement for EXO (Pb from same source) indicate lower contamination
• Total 0.03 – 0.06 events expected
Cosmogenic NeutronsMuons 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: 0.04 (stat) + 0.04– 0.03
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EvidenceCDM
S Technology
AnalysisResu
lts
ConclusionDark M
atterO
ther Analyses
Data AnalysisBackground Estimate – Surface Events, ‘Leakage’
Timing Distribution – Surface vs. Neutrons
Surface events
from Ba calibration
Nuclear recoils from Cf neutron
source
Tail distribution different for each detector determines cut position
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WIMP Search Data
EvidenceCDM
S Technology
AnalysisResu
lts
ConclusionDark M
atterO
ther Analyses
Data AnalysisBackground Estimate – Surface Events, ‘Leakage’Look at surface events outside signal region (‘sideband’)
Count events passing / failing cut – extrapolate to signal region
• 133Ba• 252Cf
Sideband 2Singles and multiples just outside NR band
Sideband 1Multiple-scatters in
NR band
Sideband 3Singles and multiples
Ba calibration in wide region
Correct for systematic
effects due to different
distributions in energy and
yield
Estimates consistent; total expected leakage from ‘blind’ data: 0.6 0.1
Leakage estimate = ------------------------------ x # signal region, failing# sideband, passing # sideband, failing
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EvidenceCDM
S Technology
AnalysisResu
lts
ConclusionDark M
atterO
ther Analyses
Data AnalysisExpected Sensitivity
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EvidenceCDM
S Technology
ConclusionDark M
atterO
ther Analyses
Data AnalysisUnblinding
masked signal region (2 NR band)
signal region
2 events near NR band
Event 1: Tower 1, ZIP 5 (T1Z5) Sat. Oct. 27, 20078:48pm CDT
Event 2: Tower 3, ZIP 4 (T3Z4) Sun. Aug. 5, 20072:41 pm CDT
Failing Cut ( Surface events)Passing Cut ( Good events)
AnalysisResu
lts
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EvidenceCDM
S Technology
ConclusionDark M
atterO
ther Analyses
Data AnalysisPost-unblinding Studies – Data Quality Recheck
Data Quality Item Resultmuon veto performance good neutralization good KS tests normal noise levels typical pre-pulse baseline rms typical background electron-recoil rate typical surface event rate typical radial position well-contained single-scatter identification good special running conditions no operator recorded issues no
Everything seems to have been in best order
AnalysisResu
lts
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EvidenceCDM
S Technology
ConclusionDark M
atterO
ther Analyses
Data AnalysisPost-unblinding Studies – Event Reconstruction
Could there be a problem with the start time of the charge pulse?
fitted start time
What is the true start time?
2 of t
he fi
ttemplate start time [ADC bin]
Closeup of template fit to ionization pulse for event 2
[ADC bin]
puls
e he
ight
(ADC
uni
ts)
A more careful accounting revised the surface event leakage estimate
from 0.6 to 0.8 events
• affects only ~1% of events with <6 keV ionization energy
• mostly accounted for in the pre-unblinding leakage estimate.
~
AnalysisResu
lts
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EvidenceCDM
S Technology
ConclusionDark M
atterO
ther Analyses
Data AnalysisCut Variation and Probabilities
1.0 10estimated surface event leakage from 133Ba
• 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
• 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.
AnalysisResu
lts
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EvidenceCDM
S Technology
ConclusionDark M
atterO
ther Analyses
Data AnalysisLikelihood 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 AnalysisResu
lts
Surface events
from Ba calibration
Nuclear recoils from Cf neutron
source
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EvidenceCDM
S Technology
ConclusionDark M
atterO
ther Analyses
Data AnalysisLimits
Minimum @ ~70 GeV CDMS new 7.0 10-8 pbCDMS combined 3.8 10-8 pb
XENON 10
CRESST 08
ZEPLIN III
EDELWEISS (09)
WARP
CDMS, new CDMS (08)
CDMS, total
AnalysisResu
lts
CDMS resutls – W. Rau - SNOLAB Workshop 2010
Expectedsensitivity
23
EvidenceCDM
S Technology
ConclusionDark M
atterO
ther Analyses
• 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
Spin Dependent InteractionPICASSO, COUPP, XENON
SuperKamiokande (p)
CRESST I
IceCube (p)
DAMA (p)CDMS (p)
COUPP (p)
PICASSO (p)
KIMS (n)
XENON (p)
KIMS (p)
XENON (n)
CDMS (n) COUPP, 4 kg(p, prelim 2010)
AnalysisResu
lts
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EvidenceCDM
S Technology
ConclusionDark M
atterO
ther Analyses
• 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
Data AnalysisInelastic Dark Matter
AnalysisResu
lts
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EvidenceCDM
S Technology
ConclusionDark M
atterO
ther Analyses
Other ResultsCoGeNT – 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)
Preliminary!!
AnalysisResu
lts
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EvidenceCDM
S Technology
ConclusionDark M
atterO
ther Analyses
Other ResultsXENON100 – Preliminary Limit
XENON 10CDMS (08)
CDMS, total
AnalysisResu
lts
XENON 100
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EvidenceAnalysis
Results
ConclusionCDM
S Technology
Dark M
atterO
ther Analyses
Other AnalysesAxions
• Solar Axions• Convert in nuclear
electric field to gg• “Bragg” condition
enhances x-section
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EvidenceAnalysis
Results
ConclusionCDM
S Technology
Dark M
atterO
ther Analyses
Other AnalysesLow 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
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EvidenceAnalysis
Results
ConclusionCDM
S Technology
Dark M
atterO
ther Analyses
Ongoing AnalysesLow Energy Threshold
• 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 experimentemploy Neganov-Luke effect (thermal signal amplification from drifting charges)
• Finalise Si analysis
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ther Analyses
AnalysisResu
lts
CDMS
TechnologyDark M
atterConclusion
Conclusion
• 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
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EvidenceConclusion
Super- heated
CryogenicDirectional
Scintillator
Fine
CDMS resutls – W. Rau - SNOLAB Workshop 2010