1. Low-threshold Results from the Cryogenic Dark Matter Search Experiment
Ray Bunker—CDMS Collaboration
WIN`11
Cape Town, South Africa

2. Ray Bunker-UCSB HEP Group
Outline
Dark Matter and WIMPs
Direct Detection
Evidence for a light WIMP
Direct
Indirect
The CDMS experiment
Detector technology
Shallow-site low-threshold analysis
Deep-site low-energy analysis
Deep-site Neutrons
February 1st, 2011
Ray Bunker-UCSB HEP Group

3. The solar neighborhood
The Dark Matter Problem
Milky Way Galactic Rotation Curve
Use interstellar gas to probe galactic
galactic mass distribution
Appears to contradict the R-1/2
falloff expected from luminous
matter
Vcircular
(km/s)
Y. Sofue, M. Honma and T. Omodaka
arXiv: v2
Radius, R (kpc)
Large uncertainties, but why should our
galaxy be any different than others?
The solar neighborhood
at ~8 kpc and ~220 km/s
Still the most compelling evidence for the existence of dark matter in the solar neighborhood!
February 1st, 2011
Ray Bunker-UCSB HEP Group

4. Cosmological Constant
The Dark Matter Problem
Komatsu et al. (WMAP), arXiv:
Concordance of observations of large-scale
structure, supernovae, and the cosmic
microwave background imply:
Only Standard Model candidate is the neutrino,
however… if
then,
Metals (us)
0.01%
Visible Baryons
0.5%
Dark Baryons 4%
Cold
Dark Matter
23%
Cosmological Constant
Dark Energy 
73%
S.A. Thomas, F. B. Abdalla, and O. Lahav,
Phys. Rev. Lett. 105, (2010).
Physics beyond the Standard Model?
February 1st, 2011
Ray Bunker-UCSB HEP Group

5. Production suppressed
WIMPsA Dark Matter Candidate
Weakly Interacting Massive Particles
Massive ↔ Structure Formation
Weakly Interacting ↔ Non-observance
Relic abundance obtained when annihilation too slow to keep up with expansion
Being produced
and annihilating
(T ≥ MWIMP)
Production suppressed
(T < MWIMP)
WIMP
quarks,
leptons,
photons
Freeze out
WIMP  1/annihilation
A Weak-scale Coincidence?
annihilation ~ weak scale
yields observed WIMP ~ ¼ !
February 1st, 2011
Ray Bunker-UCSB HEP Group

6. Ray Bunker-UCSB HEP Group
The Lightest Superpartner
No stable WIMPs in the Standard Model
SUSY extends physics beyond the SM
Lots of new particles very popular among high energy physicists
The LSP is often a WIMP
Such as the neutralino 0:
Non-appearance at LEP or Tevatron ↔ Massive (?)
Neutral ↔ Dark
Conserved R-parity ↔ Stable
LEP 0 mass bound
Chargino mass bound of ~103 GeV/c2  0 mass bound of 4060 GeV/c2
Generally presumes gaugino mass unification
February 1st, 2011
Ray Bunker-UCSB HEP Group

7. Loose Interpretation of
Light SUSY WIMPs
Relax gaugino mass unification:
The chargino & neutralino masses are basically uncorrelated
The 0 mass can evade the LEP chargino mass bound
Must invoke cosmological constraints for 0 mass bound
0-nucleon cross section (nb)
Bottino et al., Phys. Rev. D69, (2004)
0 mass (GeV/c2)
CDMS 2002 Limit
5 keV Threshold
EDELWEISS 2002
Upper Limit
Loose Interpretation of
DAMA Allowed Region
Belanger et al., J. High Energy Phys. 03 (2004) 012
0 mass (GeV/c2)
0-nucleon cross section (pb)
Scanning SUSY parameter space
Belanger et al. find 0 masses as low as 6 GeV/c2
Lines indicate the sensitivities of the ZEPLIN I (solid), ZEPLIN II (dashed), CDMS (dash-dotted) and EDELWEISS (dotted) experiments
Similarly, Bottino, Donato, Fornengo and Scopel also find 0 masses as low as 6 GeV/c2
Red points for   CDMmin
Blue points for  < CDMmin
February 1st, 2011
Ray Bunker-UCSB HEP Group

8. A low-energy threshold is critical for detecting light WIMPs!
Direct Detection
Standard assumption 
Galactic WIMP Halo
WIMP “wind” with ~220 km/s relative
velocity, or β = v/c ~ 7x10-4
Direct detection attempts to measure:
Erecoil ~ ½ Mnucleus c2 β2
~ 10 to 20 keV
Event rate  detector size,
 WIMP flux, &
 cross section
More specifically, sensitivity depends
on detector composition, WIMP
mass, detection threshold, and
halo model
Very roughly:
Rate = N [atoms] x φ [cm-2day-1] x σ [cm2/atom]
N = 8.3x1024 [atoms in a 1 kg Ge detector]
φ = 6.1x109 [cm-2day-1]
σ = 1x10-43 [cm2/atom] (weak scale cross section)
Rate = 5.1x10-9 [kg-1day-1]… totally hopeless rate per nucleon
But β << 1  Coherent scattering from entire nucleus
 ~A4 enhancement
Rate ~ (72.61)4 x 5.1x10-9 [kg-1day-1]
~ 0.1 events [kg-1day-1]… much more approachable
100 GeV/c2 WIMP
5 GeV/c2 WIMP
Ge Target
Si Target
σ = 1x10-41 cm2, vescape = 544 km/s
Dark Matter Halo
Bulge
Thick Disk
Thin Disk
Sun
A low-energy threshold is critical
for detecting light WIMPs!
February 1st, 2011
Ray Bunker-UCSB HEP Group

9. Ray Bunker-UCSB HEP Group
Direct Detection
Rate of interactions due to known backgrounds ~103 [kg-1day-1] !!!
With low threshold (~1 keV), the expected rate for a light WIMP (< 10 GeV/c2) is
much larger… ~ 10 [kg-1day-1]
Backgrounds rates increase rapidly at low energies (< 10 keV)… offsetting
higher expected rate for light WIMPs
February 1st, 2011
Ray Bunker-UCSB HEP Group

10. Ray Bunker-UCSB HEP Group
Direct Detection
Strategies for overcoming backgrounds:
Passive & active shielding
All Experiments
Minimum ionizing threshold suppression
PICASSO & COUPP
Large detector size, self shielding
DAMA & XENON
Measure 2 signals
CDMS & LUX
Event rate modulation
DAMA & DRIFT
Low threshold
CoGeNT
Pulse shape & timing
CDMS
phonons H
ionization Q
scintillation L
CDMS
EDELWEISS
CoGeNT
IGEX
DRIFT
XENON
LUX
ZEPLIN II & III
XMASS
DAMA/LIBRA
ZEPLIN I
DEAP/CLEAN NaIAD
ROSEBUD, CRESST II
CRESST I,
PICASSO,
COUPP
February 1st, 2011
Ray Bunker-UCSB HEP Group

11. Ray Bunker-UCSB HEP Group
Installing the new DAMA/LIBRA detectors in HP Nitrogen atmosphere
IMAGE CREDIT: DAMA/LIBRA Collaboration
Evidence for a Light WIMP
C. Savage et al., JCAP, 0904, 010 (2009);
& JCAP, 0909, 036 (2009);
& arXiv: v2 (2010)
The DAMA/LIBRA experiment located in the Gran Sasso
Laboratory (Italy): 200 kg of low-activity NaI operated
from September 2003 to September 2009
Annual modulation in their residual event rate with
correct phase and period… significance of ~9σ
Savage et al. have interpreted their data in terms of spin-
independent WIMP-nucleon interactions… evidence for a
light WIMP?
R. Bernabei et al., Eur. Phys. J C67, 39 (2010)
February 1st, 2011
Ray Bunker-UCSB HEP Group

12. Evidence for a Light WIMP
The CoGeNT experiment operates a ~½ kg Ge
diode detector... very low background &
very low threshold
In a short exposure, they observe an excess in
their event rate that has the exponential shape
expected for a light WIMP
C.E. Aalseth et al., arXiv: v2
D. Hooper et al. performed a combined analysis of DAMA/LIBRA and CoGeNT data and find a region of consistency that points to a WIMP with:
MWIMP ~ 7.0 GeV/c2 & σWIMP-nucleon~ 2.0x10-40 cm-2
Hooper et al., Phys. Rev. D82, (2010)
February 1st, 2011
Ray Bunker-UCSB HEP Group

13. Ray Bunker-UCSB HEP Group
Indirect Evidence for a Light WIMP
D. Hooper and L. Goodenough, arXiv: v2
D. Hooper and L. Goodenough, arXiv: v2
The FERMI Gamma Ray Space Telescope launched
in 2008
The Large Area Telescope (LAT) has observed
gamma rays from the galactic center,
300 MeV to 100 GeV
Dan Hooper & Lisa Goodenough have analyzed
the 1st two years worth of data for a WIMP
annihilation signal
Emission spectrum from 1.25° to 10° is
consistent with π0 decay, inverse Compton
scattering and Bremsstrahlung
Inner 0° to 1.25°, however, shows an excess
Profile is consistent with a cusped halo of
7-10 GeV/c2 WIMPs, annihilating primarily
into tau pairs
D. Hooper and L. Goodenough, arXiv: v2
February 1st, 2011
Ray Bunker-UCSB HEP Group

14. Ray Bunker-UCSB HEP Group
Direct Detection Low-mass WIMP Constraints
Best constraints from the XENON100 experiment... however, low-energy scale controversial:
Red dotted line = constant extrapolation
Red solid line = decreasing extrapolation
E. Aprile et al., Phys. Rev. Lett., 105, (2010).
The final CDMS II Ge limit is competitive
with 10 keV threshold:
Black solid line
Z. Ahmed et al., Science, 327, 1619 (2010).
Very low-mass limit from the CRESST,
~½ keV threshold:
Blue dashed line
G. Angloher et al., Astropart. Phys., 18, 43 (2002)
Courtesy of M. Schumann
February 1st, 2011
Ray Bunker-UCSB HEP Group

15.  0 CDMS Detector Technology Holes e- Ge or Si Crystal
Standard Ionization Measurement
Drift Electrons & Holes with
-3 to -6 V/cm Electric Field
(Applied to Ionization Electrodes)
Inner Disk
Ionization Electrode
~85% Coverage
Ge or Si Crystal 0
Holes e- 
Outer Guard Ring
Ionization Electrode
Phonon Sensors Held at Ground
February 1st, 2011
Ray Bunker-UCSB HEP Group

16. Z-sensitive Ionization & Phonon-mediated
CDMS Detector Technology Q
inner
outer D C A B R sh I
bias
SQUID array
Phonon A
feedback V
qbias
Z-sensitive Ionization & Phonon-mediated
ZIP Detector R0 R T T0
Superconducting
Quasiparticle-trap-assisted
Electrothermal-feedback
Transition-edge (QET)
phonon sensors Al
quasiparticle trap
Aluminum Collector
Tungsten
Transition Edge Sensor (TES)
Ge or Si Crystal
quasiparticle
diffusion
phonons
Cooper Pair
February 1st, 2011
Ray Bunker-UCSB HEP Group

17. Lines due to decays of internal radioisotopes tilted
CDMS Detector Technology
True recoil energy (Erecoil) measured on event-by-event basis by subtracting Luke phonons:
Ionization yield, Y ≡ Q / Erecoil
Excellent separation between electron
recoils and nuclear recoils caused by
neutrons from 252Cf source
Subtracting Luke phonons via average
ionization behavior more reliable for
low-energy nuclear recoils
Lines due to decays of internal radioisotopes tilted
Electron Recoils
Nuclear Recoils
February 1st, 2011
Ray Bunker-UCSB HEP Group

18. : reduced ionization collection
CDMS Detector Technology
Ionization yield
Phonon pulse rise time (s)
Time since trigger (s)
Phonon pulse height (V)
Surface events can be misidentified as
nuclear recoils
Phonon pulse shape and timing is
a powerful discriminator
Allows for background-free analysis
: reduced ionization collection
Bulk  Recoil
February 1st, 2011
Ray Bunker-UCSB HEP Group

19. Ray Bunker-UCSB HEP Group
CDMS Shallow-site Run
First tower of CDMS II ZIP detectors operated at shallow Stanford Underground Facility
Total Ge detector mass of ~0.9 kg and total Si mass of ~0.2 kg
“Run 21” WIMP-search data taken between December 2001
and June 2002, yielding 118 live days of raw exposure
Run 21 split into two periods distinguished by voltage bias used:
1st half with Ge (Si) operated with 3V (4V) bias voltage (3V data)
2nd half with all detectors operated with 6V bias voltage (6V data)
Analysis of 3V data with 5 keV recoil energy threshold
published in 2002… Phys. Rev., D66, (2002)
6V data previously unpublished
ZIP 1 (Ge)
ZIP 2 (Ge)
ZIP 3 (Ge)
ZIP 4 (Si)
ZIP 5 (Ge)
ZIP 6 (Si)
SQUID Readout
(phonon signals)
FET Readout
(Ionization signals)
Cold Stages
4 K to 20 mK m m
17 mwe
Active Muon Veto
Pb Shield
Fridge n
Copper n n
Polyethylene
Detectors
Inner Pb shield
February 1st, 2011
Ray Bunker-UCSB HEP Group

20. Electron Capture from L-shell Electron Capture from K-shell
CDMS Shallow-site Energy Calibration
Electron-recoil energy scale calibrated with gamma-ray sources (137Cf & 60Co)
Ge energy scale confirmed with lines
from decays of internal radioisotopes
Confirmed 11.4 day half-life of 68Ge and
0.12 ratio of L- to K-shell captures
Si scale more difficult!
Nuclear-recoil energy scale the most important
Calibrated with neutrons from 252Cf source
Ionization yield agrees well with expectation
from Lindhard theory
Ultimately, compare to GEANT simulation:
Ge scale consistent (at low energy)
Corrected Si for ~15% discrepancy
1.3 keV from 68Ge & 71Ge Decays
Electron Capture from L-shell
10.4 keV from 68Ge & 71Ge Decays
Electron Capture from K-shell
66.7 keV from
73mGe Decay
Beginning
of Run 21
End of
Run 21
Cf-252 Neutron
Calibration
Monte Carlo
Data
Preliminary
February 1st, 2011

21. CDMS Shallow-site Thresholds
ZIP 1 (Ge)
ZIP 2 (Ge)
ZIP 3 (Ge)
ZIP 4 (Si)
ZIP 5 (Ge)
ZIP 6 (Si)
SQUID Readout
(phonon signals)
FET Readout
(Ionization signals)
Cold Stages
4 K to 20 mK
ZIP 1 rejected as a low-threshold detector
Hardware trigger efficiency:
Average ionization yield used to estimate recoil energy
Hardware thresholds vary from ~0.7 to 1.8 keV
Software phonon energy threshold
Based on Gaussian width of sub-threshold noise
Events required to exceed 6σ noise width
Software thresholds vary from ~0.6 to 1.6 keV
Ultimate threshold efficiency
Ge thresholds 0.7 to 1.1 keV
Si thresholds 1.5 to 1.9 keV
ZIP 4 (Si)
Total Phonon Energy (keV)
Run Number (6V data)
ZIP 2 (Ge)
Total Phonon Energy (keV)
Run Number (3V data)
February 1st, 2011

22. Shallow-site Neutrons Compton γ Electron Recoils
CDMS Shallow-site Event Selection Ge Si
1.3 keV Line
32% 0%
Zero-charge Events
30-40%
Shallow-site Neutrons 6% 2%
Compton γ Electron Recoils
10-20%
14C Contamination β’s
40%
Others
2-22%
0-18%
WIMP candidates must pass several data cuts:
Data-quality cuts  % efficient
Fiducial-volume cut  ~83% efficient
Single-scatter criterion  % efficient
Muon-veto cut  ~70-80% efficient
Nuclear-recoil cut  ~95% efficient
Combined data cuts  ~50-60% efficient
1080 candidate events in 72 kg-days of Ge exposure
970 candidate events in 25 kg-days of Si exposure
Are these really WIMPs?... probably not!
While a low-mass WIMP could be hiding in
these data, we can claim no evidence of a
WIMP signal
1080 Candidates
970 Candidates
Raw Spectrum in Blue
Corrected for Cut Efficiency in Black
Further Corrected for Threshold Efficiency in Orange
Average Combined Efficiencies in Orange
90% (statistical) Lower-limit Efficiencies in Blue
Inner electrode ionization energy (keV)
Outer electrode ionization energy (keV)
202 Candidates
130 Candidates
314 Candidates
February 1st, 2011
Ray Bunker-UCSB HEP Group

23. Exclude new parameter space for WIMP masses between 3 and 4 GeV/c2!
CDMS Shallow-site Low-threshold Limits
Hooper et al. combined: Gray
CDMS Shallow-site Ge: Black —
CDMS Shallow-site Si: Gray —
CoGeNT 2010: Orange ---
CRESST Saphire 2002: Blue ---
XENON100 Decreasing: Red —
XENON100 Constant: Red ····
Large background uncertainties preclude background subtraction
We use Steve Yellin’s Optimum Interval Method
(specially adapted for high statistics)
Serialize detector intervals to make best
use of lowest-background detectors
Include the effect of finite
energy resolution near threshold
Standard WIMP halo model with
544 km/s galactic escape velocity
Systematic studies indicate limits
are robust above ~3 GeV/c2
D. Akerib et al. (CDMS), Phys. Rev. D82, (2010)
Exclude new parameter space for WIMP
masses between 3 and 4 GeV/c2!
February 1st, 2011
Ray Bunker-UCSB HEP Group

24. Ray Bunker-UCSB HEP Group
The CDMS Deep Site
17 mwe at SUF yielding
~500 Muons per second
in the CDMS shielding
5.2x104 m-2y-1
2100 mwe
2100 mwe at Soudan yielding
<1 Muon per minute
in the CDMS shielding
February 1st, 2011
Ray Bunker-UCSB HEP Group

25. Ray Bunker-UCSB HEP Group
The CDMS Deep Site
February 1st, 2011
Ray Bunker-UCSB HEP Group

26. CDMS Deep-site Low-energy Analysis
Focused low-energy analysis of CDMS WIMP-search data taken at the Soudan Mine
5 Towers of ZIP detectors (30 total) operated from October 2006 to September 2008 (6 distinct runs)
8 lowest-threshold Ge detectors
analyzed with 2 keV threshold

27. Ray Bunker-UCSB HEP Group
CDMS Deep-site Low-energy WIMP Candidates
Optimized nuclear-recoil selection to avoid zero-charge event background
Band thickness due to variations in nuclear-recoil criterion from run to run
Recoil energy estimated from phonon signal & average ionization yield behavior
Tower 1-ZIP 5
February 1st, 2011
Ray Bunker-UCSB HEP Group

28. Ray Bunker-UCSB HEP Group
CDMS Deep-site Low-energy Backgrounds
A factor of ~10 reduction in background levels
Improved estimates of individual background
sources
Comparable detection efficiency for much larger
exposure (~3.5x)
No evidence of a WIMP signal
Candidate Spectrum: Black Error Bars
Zero-charge Events: Blue Dashed
Surface Events: Red +
Bulk Compton γ Events: Green Dash-dotted
1.3 keV Line: Pink Dotted
Combined Background: Black Solid
Average Efficiency
February 1st, 2011
Ray Bunker-UCSB HEP Group

29. Ray Bunker-UCSB HEP Group
CDMS Deep-site Low-energy Limit
Z. Ahmed et al. (CDMS), arXiv: v1 (submitted to Phys. Rev. Letters)
Hooper et al. combined: Gray
CDMS Shallow-site Ge: Black —
CDMS Shallow-site Si: Gray —
CRESST Saphire 2002: Blue ---
XENON100 Decreasing: Orange —
XENON100 Constant: Orange ····
CDMS Deep-site Ge: Red —
February 1st, 2011
Ray Bunker-UCSB HEP Group

30. Ray Bunker-UCSB HEP Group
CDMS Deep-site Low-energy Spin-dependent Limit
CDMS II Ge Deep-site
10 keV Threshold
CRESST
Saphire 2002
3σ DAMA Allowed Region
CDMS II Ge Deep-site
2 keV Threshold
XENON10
February 1st, 2011
Ray Bunker-UCSB HEP Group

31. Ray Bunker-UCSB HEP Group
Deep-site Neutron Background
Less than one event expectec for CDMS II
Limiting background for SuperCDMS… but how soon?
February 1st, 2011
Ray Bunker-UCSB HEP Group

32. Ray Bunker-UCSB HEP Group
Fast-neutron Detection
High Energy Neutron
No Veto, Small Prompt
Energy Deposit
Veto   
Liquid Scintillator
Gadolinium Loaded  
Capture on Gd, Gammas
(spread over 40 μs)
PMT
Liberated Neutrons
PMT
Lead
Hadronic Shower
Veto
Veto
February 1st, 2011
Ray Bunker-UCSB HEP Group

33. Fast-neutron Detection
Expected Number of sub-10 MeV
Secondary Neutrons
Simulated 100 MeV Neutrons
Incident on Lead Target
Detectable Neutron Multiplicity
February 1st, 2011
Ray Bunker-UCSB HEP Group

34. Ray Bunker-UCSB HEP Group
A Fast-neutron Detector
February 1st, 2011
Ray Bunker-UCSB HEP Group

35. Ray Bunker-UCSB HEP Group
Detector Installation
Electronics Rack
Lead Target
Source Tubes
February 1st, 2011
Ray Bunker-UCSB HEP Group

36. Ray Bunker-UCSB HEP Group
Detector Installation
Cheap Labor
Water Tanks
February 1st, 2011
Ray Bunker-UCSB HEP Group

37. Ray Bunker-UCSB HEP Group
Detector Installation
20” KamLAND
Phototubes
February 1st, 2011
Ray Bunker-UCSB HEP Group

38. Ray Bunker-UCSB HEP Group
Neutron Detection Technique
Water-based neutron detector is challenging!
Small fraction of energy visible as Cerenkov
radiation
Poor energy resolution smears U/Th gammas
into signal region
February 1st, 2011
Ray Bunker-UCSB HEP Group

39. Ray Bunker-UCSB HEP Group
Neutron Detection Technique
Timing is Everything
Neutron capture times  microseconds
A few 100 Hz of U/Th background  milliseconds
February 1st, 2011
Ray Bunker-UCSB HEP Group

40. Ray Bunker-UCSB HEP Group
Neutron Detection Technique
More Gamma Like
Background U/Th
Gamma Rays
252Cf Fission Neutrons
Pulse timing Likelihood
More Neutron Like
Pulse Height Likelihood
February 1st, 2011
Ray Bunker-UCSB HEP Group

41. Ray Bunker-UCSB HEP Group
Understanding Energy Scale
Background U/Th
Gamma Rays
Actual data: shaded red
Simulated data: black lines
252Cf Fission
Neutrons
Pulse height (mV)
Event rate (arbitrary units)
60Co ~1 MeV
Gamma Rays
Pulse height (mV)
February 1st, 2011
Ray Bunker-UCSB HEP Group

42. Ray Bunker-UCSB HEP Group
Understanding Energy Scale
Event rate (arbitrary units)
~150 MeV
Pulse height (V)
~50 MeV Endpoint
February 1st, 2011
Ray Bunker-UCSB HEP Group