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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

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Results from the Cryogenic Dark Matter Search

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Results from the cryogenic dark matter search

Results from the

Cryogenic Dark Matter Search

Wolfgang Rau

On behalf of the CDMS collaboration


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

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


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

Overview

  • Introduction – Dark Matter

  • CDMS technology

  • Data Analysis and WIMP Results

  • Other Results (time permitting)


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

Abell 2218 (HST)

Coma Cluster

Introduction – Dark Matter

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

WMAP

Other

Analyses

Conclusion

Gravitational Lensing

Bullet Cluster


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

Thermal

bath

Thermal coupling

Phonon sensor

e

n

+

+

+

-

-

Target

-

Ionization energy [keVeeq]

-

+

+

-

-

+

+

-

+

+

+

+

Phonon energy [keV]

-

-

-

-

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

Dark

Matter

Evidence

CDMS

Technology

Analysis

Results

Other

Analyses

Electron recoils

from β’s and γ’s

Phonon signal

Conclusion

Electron recoil

Nuclear recoil

Charge signal

Nuclear recoils

from neutrons


Results from the cryogenic dark matter search

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


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

gs

Detector

Collimator

g-band

rising edge slope

bs

+

surface event

E

nuclear recoil

+

neutrons

+

+

+

+

+

+

n-band

+

CDMS Technology

Detector Performance

Dark

Matter

Evidence

CDMS

Technology

Ionization/Recoil energy

b-band

Analysis

Results

Recoil energy [keV]

Other

Analyses

Surface effect

Conclusion

Reduced charge signalbut faster phonon signal


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

CDMS Technology

Experimental Setup

Soudan

Underground lab

(2000 m w.e.)

„Tower“

(6 Detectors)

Dark

Matter

Evidence

CDMS

Technology

Analysis

Results

Cryostat, Coldbox

Shielding

Other

Analyses

Conclusion

5 Towers (~ 5 kg Ge ) operated 2006 – 2008


Results from the cryogenic dark matter search

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

CDMS

Technology

Analysis

Results

Amplitude [a.u.]

Other

Analyses

Conclusion

Time bins [0.8 s]


Results from the cryogenic dark matter search

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

Fraction of low yield events

Analysis

Results

Date

Other

Analyses

average

5 above average

(colored points = poorly neutralized datasets)

Conclusion

datasets

templates


Results from the cryogenic dark matter search

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

periods of poor data quality removed

raw exposure

Other

Analyses

this work

Conclusion

2008 published data


Results from the cryogenic dark matter search

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


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

Data Analysis

Background Estimate – Neutrons

Dark

Matter

Evidence

  • 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: 0.04 (stat)

CDMS

Technology

Analysis

Results

Other

Analyses

Conclusion

+ 0.04

– 0.03


Results from the cryogenic dark matter search

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


Results from the cryogenic dark matter search

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

CDMS

Technology

Sideband 1

Multiple-scatters in NR band

Sideband 2

Singles and multiples just outside NR band

Sideband 3

Singles and multiples Bacalibration in wide region

Analysis

Results

  • 133Ba

  • 252Cf

WIMP Search Data

Correct for systematic effects due to different distributions in energy and yield

Other

Analyses

Conclusion

# sideband, passing

# sideband, failing

Leakage estimate = ------------------------------ x # signal region, failing

Estimates consistent; total expected leakage from ‘blind’ data: 0.6  0.1


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

Data Analysis

Expected Sensitivity

Dark

Matter

Evidence

CDMS

Technology

Analysis

Results

Other

Analyses

Conclusion


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

2 events near NR band

Data Analysis

Unblinding

Dark

Matter

Evidence

CDMS

Technology

Event 1:

Tower 1, ZIP 5 (T1Z5)

Sat. Oct. 27, 2007

8:48pm CDT

signal region

Analysis

Results

masked signal region (2 NR band)

Other

Analyses

Conclusion

Failing Cut ( Surface events)

Passing Cut ( Good events)

Event 2:

Tower 3, ZIP 4 (T3Z4)

Sun. Aug. 5, 2007

2:41 pm CDT


Results from the cryogenic dark matter search

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


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

Closeup of template fit to ionization pulse for event 2

fitted start time

pulse height (ADC units)

2 of the fit

What is the true start time?

[ADC bin]

template start time [ADC bin]

Data Analysis

Post-unblinding Studies – Event Reconstruction

Could there be a problem with the start time of the charge pulse?

Dark

Matter

Evidence

CDMS

Technology

Analysis

Results

Other

Analyses

  • affects only ~1% of events with <6 keV ionization energy

  • mostly accounted for in the pre-unblindingleakage estimate.

~

Conclusion

A more careful accounting revised the surface event leakage estimatefrom 0.6 to 0.8 events


Results from the cryogenic dark matter search

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.


Results from the cryogenic dark matter search

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


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

Data Analysis

Limits

Dark

Matter

Evidence

CDMS

Technology

WARP

Analysis

Results

CRESST 08

EDELWEISS (09)

Other

Analyses

ZEPLIN III

CDMS (08)

Expectedsensitivity

CDMS, new

CDMS, total

Conclusion

XENON 10

Minimum @ ~70 GeV

CDMS new7.0  10-8pb

CDMS combined3.8 10-8pb


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

Spin Dependent Interaction

PICASSO, COUPP, XENON

Dark

Matter

Evidence

  • 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

KIMS (n)

CDMS

Technology

COUPP (p)

CDMS (p)

CRESST I

DAMA (p)

Analysis

Results

COUPP, 4 kg(p, prelim 2010)

PICASSO (p)

KIMS (p)

CDMS (n)

Other

Analyses

XENON (n)

SuperKamiokande (p)

Conclusion

XENON (p)

IceCube (p)


Results from the cryogenic dark matter search

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


Results from the cryogenic dark matter search

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


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

Other Results

XENON100 – Preliminary Limit

Dark

Matter

Evidence

CDMS

Technology

WARP

Analysis

Results

CRESST 08

EDELWEISS (09)

CDMS (08)

Other

Analyses

ZEPLIN III

CDMS, new

CDMS, total

Conclusion

XENON 10

XENON 100


Results from the cryogenic dark matter search

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


Results from the cryogenic dark matter search

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


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

Ongoing Analyses

Low Energy Threshold

Dark

Matter

Evidence

CDMS

Technology

  • 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

Analysis

Results

Other

Analyses

Conclusion


Results from the cryogenic dark matter search

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


Results from the cryogenic dark matter search

CDMS resutls – W. Rau - SNOLAB Workshop 2010

Fine

Evidence

Cryogenic

Super-

heated

Scintillator

Directional

Conclusion


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