results from the cryogenic dark matter search wolfgang rau on behalf of the cdms collaboration

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

ConclusionCD

MS

TechnologyD

ark 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.


5

EvidenceAnalysis

Results

Conclusion

CDMS TechnologyOperating Principle

CDM

S Technology

Dark

Matt

erO

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 s

igna

lCh

arge

sig

nal

Electron recoil Nuclear recoil


6

EvidenceAnalysis

Results

Conclusion

CDMS TechnologyDetectors

CDM

S Technology

Dark

Matt

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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


7

EvidenceAnalysis

Results

ConclusionCD

MS

TechnologyD

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Other

AnalysesCDMS Technology

Detector 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


8

EvidenceAnalysis

Results

ConclusionCD

MS

TechnologyD

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Other

AnalysesCDMS Technology

Experimental Setup

„Tower“(6 Detectors)

Cryostat, ColdboxShielding

SoudanUnderground lab(2000 m w.e.)

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


9

EvidenceCD

MS

TechnologyAnalysis

Results

ConclusionD

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Other

AnalysesData Analysis

Event 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


10

EvidenceCD

MS

TechnologyAnalysis

Results

ConclusionD

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Other


Data Quality

Fra

ctio

n of

low

yie

ld e

vent

s

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


11

EvidenceCD

MS

TechnologyAnalysis

Results

ConclusionD

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Other


Data 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


12

EvidenceCD

MS

TechnologyAnalysis

Results

ConclusionD

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Other


Position Dependent Calibration

Tim

ing parameter

Position Dependence of Timing Parameter (measured with e-recoils)

events near and outside fiducial volume

increasin

g radius

Radi

us fr

om a

rriv

al ti

me

Radius from energy partition

• 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

Improvement in this analysis Include s outside fiducial volume in lookup table reduces timing outliers from miscalibration


13

EvidenceCD

MS

TechnologyAnalysis

Results

ConclusionD

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Other


Background Estimate – Neutrons

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) + 0.04– 0.03


14

EvidenceCD

MS

TechnologyAnalysis

Results

ConclusionD

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Other


Background 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


15

WIMP Search Data

EvidenceCD

MS

TechnologyAnalysis

Results

ConclusionD

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Other


Background Estimate – Surface Events, ‘Leakage’

Look at surface events outside signal region (‘sideband’)Count events passing / failing cut – extrapolate to signal region

• 133Ba• 252Cf

Sideband 2

Singles and multiples just outside NR band

Sideband 1

Multiple-scatters in NR band

Sideband 3

Singles 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


16

EvidenceCD

MS

TechnologyAnalysis

Results

ConclusionD

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Other


Expected Sensitivity


17

EvidenceCD

MS

TechnologyConclusion

Dark

Matt

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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


18

EvidenceCD

MS


Dark

Matt

erO

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


19

EvidenceCD

MS


Dark

Matt

erO

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

(AD

C un

its)

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


20

EvidenceCD

MS


Dark

Matt

erO

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


21

EvidenceCD

MS


Dark

Matt

erO

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


22

EvidenceCD

MS


Dark

Matt

erO

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


Expectedsensitivity

23

EvidenceCD

MS


Dark

Matt

erO

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


24

EvidenceCD

MS


Dark

Matt

erO

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


25

EvidenceCD

MS


Dark

Matt

erO

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


26

EvidenceCD

MS


Dark

Matt

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ther Analyses

Other ResultsXENON100 – Preliminary Limit

XENON 10CDMS (08)

CDMS, total

AnalysisResu

lts

XENON 100


27

EvidenceAnalysis

Results

ConclusionCD

MS

TechnologyD

ark M

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Other

AnalysesOther Analyses

Axions

• Solar Axions• Convert in nuclear

electric field to • “Bragg” condition

enhances x-section


28

EvidenceAnalysis

Results

ConclusionCD

MS

TechnologyD

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Other

AnalysesOther 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


29

EvidenceAnalysis

Results

ConclusionCD

MS

TechnologyD

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Other

AnalysesOngoing Analyses

Low 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


30O

ther Analyses

AnalysisResu

lts

CDM

S Technology

Dark

Matt

erConclusion

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


31

EvidenceConclusion

Super- heated

CryogenicD

irectionalScintillator

Fine


results from the cryogenic dark matter search wolfgang rau on behalf of the cdms collaboration

Documents

syracuse university

university of minnesota

cdms collaboration slide

rau santa clara university

supercdms cdms resutls

s phonon signal

cooley stanford university

huber university of