Dark Matter Direct Detection:Dark Matter Direct Detection: CDMS

Vuk MandicUniversity of MinnesotaUniversity of Minnesota

13. July 2010

CDMS II CollaborationCalifornia Institute of TechnologyZ. Ahmed, J. Filippini, S.R. Golwala, D. Moore, R.W. Ogburn

Case Western Reserve UniversityD. Akerib, C.N. Bailey, M.R. Dragowsky, D R Grant R Hennings-Yeomans

Stanford UniversityP.L. Brink, B. Cabrera, M. Cherry *, L. Novak, M. Pyle, A. Tomada, S. Yellin

Syracuse UniversityM K M Ki i R W S hD.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 Technology

M. Kos, M. Kiveni, R. W. Schnee

Texas A&MJ. Erikson *, R. Mahapatra, M. Platt *

University of California, BerkeleygyE. Figueroa-Feliciano, S. Hertel, S.W. Leman, K.A. McCarthy, P. Wikus

NIST *K. Irwin

Q ’ U i it

M. Daal, N. Mirabolfathi, A. Phipps, B. Sadoulet,D. Seitz, B. Serfass, K.M. Sundqvist

University of California, Santa BarbaraR. Bunker, D.O. Caldwell, H. Nelson, J. Sander

University of Colorado DenverQueen’s UniversityP. Di Stefano *, N. Fatemighomi *, J. Fox *, S. Liu *, P. Nadeau *, W. Rau

Santa Clara UniversityB. A. Young

University of Colorado DenverB.A. Hines, M.E. Huber

University of FloridaT. Saab, D. Balakishiyeva, B. Welliver *

University of MinnesotaSouthern Methodist UniversityJ. Cooley

SLAC/KIPAC *E. do Couto e Silva, G.G. Godrey, J. Hasi, C J Kenney P C Kim R Resch J G Weisend

University of MinnesotaJ. Beaty, H. Chagani *, P. Cushman, S. Fallows, M. Fritts, O. Kamaev, V. Mandic, X. Qiu, A. Reisetter, J. Zhang

University of ZurichS. Arrenberg, T. Bruch, L. Baudis, M. Tarka

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C. J. Kenney, P. C. Kim, R. Resch, J.G. Weisend

* new collaborators or new institutions in SuperCDMS

Cryogenic Dark Matter Searchy g

• Search for Dark Matter in the form of WIMPs.Id tif / ll k f f ti l i t ti– Identify/suppress all known forms of particle interactions.

• Cosmogenic:– Deep underground: Soudan mine, Minnesota, 713m below surface.– Muon scintillator veto: Reject muon-coincident events.j

• Ambient neutron and electromagnetic background:– Passive shielding: Pb and polyethylene.

• Residual gamma and beta backgrounds:Ge/Si based detectors cooled to ~40 mK– Ge/Si-based detectors cooled to ~40 mK

– Phonon and ionization signals– Event-by-event identification

• Remaining neutron background:

WIMP Terrestrial Particle Detector

– Ge vs Si event rates– Single vs multiple event rates

energy transferred appears in ‘wake’ of recoiling nucleus

WIMP-Nucleus Scattering 3

CDMS II Detector: ZIP• Z-sensitive Ionization and Phonon

Detector3” di t 1 thi k 250 (G ) R

SQUID array Phonon D

– 3” diameter, 1cm thick, 250 g (Ge)• Sensors deposited and

photolithographicaly patterned on the surface

Rbias

I bias

Rfeedback

surface.• Two charge/ionization electrodes on

one surface:– Inner disk and outer ring.

A

B

D

Cg• Four phonon sensors, each covering

one quadrant, on the opposite surface. Q inner

Q outer

Vqbias

4

Ionization and Phonon SignalsIonization and Phonon Signals• Ionization:

Fast: 1 s rise time 40 s fall time- Fast: 1 μs rise-time, 40 μs fall-time.- Good measure of the Event Time.

• Phonons:A D- Pulse shape (start-time, rise-time,

energy distribution among 4 quadrants) depends on event position.

B C

• Ionization and Phonon signal amplitudes reveal the recoil energy.

• Timing and amplitude of the phonon signals can be used to reconstruct event position.

• Allows position correction of any non-uniformities (Tc gradient). 5

Ionization YieldIonization Yield

Calibration DataIonization yield: ionization signal

13x our WIMP-search backgroundCalibration Datay g

divided by recoil energy.

133Ba γ-source used to define the electron recoil bandelectron-recoil band.

252Cf n-source used to define the nuclear-recoil band.

The bands are well separated down to below 10 keV!

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Ionization Yield

Ionization yield: ionization signal Calibration Data

Ionization Yield

y gdivided by recoil energy.

133Ba γ-source used to define the electron recoil band

13x our WIMP-search backgroundCalibration Data

electron-recoil band.

252Cf n-source used to define the nuclear-recoil band.

The bands are well separated down to below 10 keV!

Small fraction of electron-recoils trickles down to the nuclear recoil band – surface events!

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Surface-Event RejectionjCalibration Data

Rej

ect

R

Keep

• Phonon pulse-shape contains p pinformation on interaction depth:

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WIMP Search Exposure

Total raw exposure is 612 kg days

WIMP Search Exposure

Total raw exposure is 612 kg-days

some detectors not analyzed for WIMP scatters

recorded data

WIMP scatters

periods of poor data quality

removed

this work

Data taken

2008 result

from 9/08-3/09: primarily an engineering

PRL102, 011301(2009)

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engineering run

Runs 125-128: Blind AnalysisAll WIMP search data

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We unblinded the signal region November 5, 2009

Events Failing Timing CutAll WIMP search data

failing the timing cut

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150 events in the NR band fail the timing cut, consistency checks deemed ok

Events Passing Timing CutAll WIMP search data passing the timing cut

Event 1: Tower 1, ZIP 5 (T1Z5) Sat Oct 27 2007Sat. Oct. 27, 20078:48pm CDT

Event 2: Tower 3 ZIP 4 (T3Z4)Tower 3, ZIP 4 (T3Z4) Sun. Aug. 5, 20072:41 pm CDT

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2 events in the NR band pass the timing cut!

WIMP Signal?WIMP Signal?• 2 candidate events:

– Periods of nearly ideal experimental performance.– Different months, different detectors.– So, maybe…

• Expected backgrounds:– Surface event leakage (based on calibration studies): 0.8 ± 0.2 events.– Neutron background: <0.1 events.

• Cosmogenic and radiogenic.• Data, Simulations, Counting.

• 23% probability of observing 2 or more events, given these backgrounds.• Results of this analysis cannot be interpreted as significant evidence

for WIMP interactions, but we cannot reject either event as signal.

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90%CL Spin-Independent LimitIn the presence of 2 events

(no bg subtraction):

CDMS Combined Soudan Data @WIMP mass 70 GeV@WIMP mass 70 GeV

σ = 3.8 x 10-44 cm2 (90% C.L.)

Sensitivity curve assuming:

0.8 ±0.1(stat.) ±0.2(sys.) surface events ( ) ( y )0.04 cosmogenic neutrons 0.04 − 0.06 radiogenic neutrons

+ 0.04 - 0.03

Science 327, 1619 (2010)

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Runs 123-124: Low Energy• Electromagnetic signatures in

CDMS detectors – possibly new Observed Electron Recoil Spectrump yphysics.

• Similar to our standard analysis:– Use electron-recoil events.

Observed Electron-Recoil Spectrum

– Do not impose timing cut.• Low recoil energies particularly

interesting.• Understand the backgrounds well.

– Several lines due to cosmogenic activation.Li idth ( l ti )– Line widths (energy resolution) well understood.

• Use 2-8.5 keV window.Feature at 6 54 keV likely due– Feature at 6.54 keV likely due to de-excitation of 55Mn (cosmogenic activation). 15

PRD81, 042002 (2010)

Solar Axion BackgroundSolar Axion Background• Axion-photon coupling:

Time and energy dependence of solar axion conversion rate for

10 8 G V 1– In Coulomb field of the nucleus,

a → γ.– Recoil energy = incident energy.

gaγγ=10-8 GeV-1

• Standard solar model gives the axionflux:

• Coherent Bragg diffraction: momentum transfer equal to reciprocal lattice vectorvector.– For a given direction (sky location)

there are preferred recoil energies.• Complex modulation pattern, PRL103 141802 (2009)Co p e odu at o patte ,

dependent on incident/recoil energy.16Sets the relevant energy scale

PRL103, 141802 (2009)

Solar Axion BackgroundSolar Axion Background• Similar studies were done in the past:

– SOLEX, COSME, DAMA…SOLEX, COSME, DAMA…• New feature: angular orientation is

well understood:– Uncertainty of 3° dominated by y y

the relative tower-cryostat orientation.

• Place a new 95% CL on the axion-h t liphoton coupling:

gaγγ < 2.4 × 10-9 GeV-1

• Applies to axion mass below 0.1 keV.– Larger masses suppressed in the

solar axion flux.• Expect ~10x improvement with

SuperCDMS-100 kg. 17

PRL103, 141802 (2009)

Galactic Axion BackgroundGalactic Axion Background• Repeat the analysis for galactic

axions.– Non-relativistic, axio-electric

coupling.Si l t th i– Signal appears at the axionrest mass.

• Place an upper limit on gaee at each axion massaxion mass.

gaee < 1.4 × 10-12

for a 2.5 keV axion• Incompatible with galactic axion

interpretation of DAMA signal.• 55Mn feature at 6.54 keV not

b d ( di iPRL103, 141802 (2009)

subtracted (no direct constraint on this contribution).

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Low-Energy SpectraLow Energy Spectra• Can attempt a comparison with

DAMA/LIBRA signal, in the 90% CL upper limitsginterpretation of electromagnetic energy deposition by WIMPs.

• Big uncertainty – how does cross ti h b t G dsection change between Ge and

NaI?– Assume Z2 dependence.

Scale CDMS (Ge) rate to– Scale CDMS (Ge) rate to estimate total rate in NaI.

– Compare with total rate observed by DAMA at the 3.15 ykeV peak.

• Observe large discrepancy.– Could be reduced if the 40K

PRD81 042002 (2010)contamination is understood (leading to a 3.2 keV line). 19

PRD81, 042002 (2010)

Outlook:CDMS II S CDMS GEODMCDMS II SuperCDMS GEODM

CDMS II3” x 1cm ~ 0.25 kg/det16 detectors = 4 kg~2 yrs operation

SuperCDMS3” x 1” ~ 0.64 kg/detSoudan SNOlab25 d t t 15 k 150 d t t 100 k25 detectors = 15 kg 150 detectors = 100 kg2 yrs ~ 8000 kg-d 3 yrs ~ 38000 kg-d

SuperCDMS SNOlab and Ge-ObservatorySuperCDMS SNOlab and Ge-Observatory for Dark Matter (GEODM) 6” x 2” ~ 5.1 kg/detSNOlab DUSEL20 d t t 100 k 300 d t t 1 5 t20 detectors = 100 kg 300 detectors = 1.5 ton3 yrs ~ 100,000 kg-d 4 yrs ~ 1.5 Mkg-d

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New Technology: iZIP DetectoriZIP Detector

• Improved yield=Q/P performance:– Surface rejection: 1:3000 (currently

1:350)– Less Al, tangential E-field.

• Ionization side asymmetry:– Surface rejection: 1:1000

• Phonon timing and symmetry between two sides:– Surface rejection: 1:3000– Likely correlations with other two

parameters.M t i t f th t l• Meets requirements for the ton-scale experiment.– Could not measure overall

rejection efficiency in a surfacerejection efficiency in a surface facility (cosmogenic neutrons dominate over the surface leakage).

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Spare SlidesSpare Slides

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Fit DAMA/LIBRA SpectrumFit DAMA/LIBRA Spectrum

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Maximum Likelihood Analysis (A i d l )(Axion models)

S l i flSolar axion flux

Expected rate (solar)

Rate model (solar)

Background rate modelBackground rate model

E pected rate (galactic)

Likelihood definition

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Expected rate (galactic)

mZIPmZIP• Minor design changes.• 1” thick 2 5x suppression of• 1 thick, 2.5x suppression of

surface events.• “Stadium” phonon sensor

design:g– Covers more surface area– Improves phonon collection

and SNR.• “Mercedes”-like phonon sensor

layout.– Better phonon signal at the

t douter edge.– Breaks degeneracies in

position reconstruction.Improves phonon timing– Improves phonon timing information.

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mZIP at Soudan

• Meets requirements for 15-kg

mZIP at Soudan

stage (possibly even beyond).• SuperTower 1 installed at Soudan.

– Five 1”-thick detectors + 2 end-t d t tcap veto detectors.

– Started to look at the data.

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Phonon Sensorsquasiparticle

trapAl Collector W

T iti Edquasiparticle

Al

Transition-Edge

Sensor

Si G

diffusion

Si or Gephonons

W Transition-Edge Sensor:

• Measurement of athermal phonon signals maximizes information normal

a really good thermometer

Ω)

4

3

~ 10mK

g

• Fast pulse, excellent energy and timing resolution

R TES

(Ω 3

2

1timing resolution

superconductingT (mK)Tc ~ 80mK

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Phonon Sensors

60 μm wide

380 μm Al fins

• 4 quadrants• 4 quadrants • 37 cells per quadrant• 6x4 array of W transition-edge sensors per cell• Each W sensor “fed” by 8 Al finsy⇒ ~1000 TES per quadrant, wired in parallel!

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Phonon Signal ReadoutPhonon Signal Readout

10 pA/√Hz

• First-stage amplification:– Low-noise SQUID-based

10 pA/√Hz

amplifier.– SQUIDs operated at 600 mK.

• Current through the sensor ~1μA. Bandwidth ~ 70 kHz– Amplified 10x by the SQUID.– Further amplification at room

temperature.29

Ionization Electrodes & ReadoutIonization Electrodes & Readout• Phonon sensors also serve as ground

for ionization readout.• Opposite side has two electrodes:

– Inner disk, outer ring.– Defines fiducial volume: reject

events close to the edge.• First-stage amplification:

FET b d lifi– FET-based amplifier.• High-impedance:

– Susceptible to microphonics ⇒vacuum coaxvacuum coax.

– Keep gate wire short ⇒ FET must be in the cryostat ⇒ heat load.

– These are major drivers of the coldSub-microsecond rise-timeR C 40 f ll ti– These are major drivers of the cold

hardware design.RFCF ⇒ 40μs fall-time

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Ionization Channel NoiseIonization Channel Noise• Amplifier bandwidth ~160 kHz.• Noise consistent with 0.5 nV/√Hz

of the FET.• Equivalent to ~1 keV energy

th h ldthreshold.

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Position ReconstructionPosition Reconstruction• Exposed one detector to a large-surface 109Cd source, behind a Pb Event-position reconstructed collimator. using phonon start-times.

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