CDMS
UCSB
CDMS II
CDMS
The New Cosmology Confronts
Observation
KITP
August 21, 2002
Harry Nelson
UCSB
UCSB
CDMS II
Physics Motivation
• Several Arguments for
Dark Matter
• Milky Way’s Rotation
Curve
Θ
R
August 21, 2002
Θ
220 km/s
⊕
R
• Massive Particle Popular
• Weak Interactions (WIMP):
» Dark/Luminous Balance
» SUSY Broken at Weak
Scale… χ0 (neutralino)
KITP NCCO - Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
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CDMS
UCSB
CDMS II
WIMP/nucleon σ≈10-42 cm
Exper.
CDMS
DAMA
Theory
SUSY,
various constraints
including Big Bang
August 21, 2002
UCSB
3
KITP NCCO - Harry Nelson
CDMS II
Direct Detection
Signal
Background
Nucleus
Recoils
Electron
Recoils
Er
v/c ≈ 10-3
Dense Energy Deposition
v/c small; Bragg
Er
v/c ≈ 0.3
Sparse Energy Deposition
Neutrons same, but
σ≈1020 higher - shield
χ0
August 21, 2002
γ
Density/Sparsity
Basis of Discrimination
KITP NCCO - Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
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CDMS
UCSB
Rate, Energy Spectrum
∝A2
CDMS II
MWIMP=100 GeV
σ = 10-42 cm2/nucleon
Silicon, Sulphur
Germanium
Iodine, Xenon
Nucleus
Recoils
Er
Diffraction off Nucleus
χ0
Slope: Maxwell-Boltzmann
WIMPs in Galaxy
August 21, 2002
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KITP NCCO - Harry Nelson
UCSB
CDMS II
The CDMS Collaboration
Case Western Reserve University
D.S. Akerib,D. Driscoll, S. Kamat,
T.A. Perera, R.W. Schnee, G.Wang
Fermi National Accelerator Laboratory
M.B. Crisler, R. Dixon,
D. Holmgren
Lawrence Berkeley National Lab
R.J. McDonald, R.R. Ross
A. Smith
Nat’l Institute of Standards & Tech.
J. Martinis
Princeton University
T. Shutt
Santa Clara University
Stanford University
L. Baudis, P.L. Brink, B. Cabrera,
C. Chang, W. Ogburn, T. Saab
University of California, Berkeley
S. Armel, V. Mandic, P. Meunier,
W. Rau, B. Sadoulet
University of California, Santa Barbara
D.A. Bauer, R. Bunker,
D.O. Caldwell, R. Ferril,
R.Mahapatra, H.Nelson, R. Nelson,
J.Sander, C. Savage, S. Yellin
University of Colorado at Denver
M. E. Huber
Brown University
R.J. Gaitskell, J.P. Thomson
B.A. Young
August 21, 2002
KITP NCCO - Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
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3
CDMS
UCSB
CDMS II
The CDMS Experiments (Cryogenic Dark Matter Search)
Operate at ≈ 20 mKelvin
Use Germanium (WIMPs) and Silicon (neutrons)
Simultaneously measure charge (Q) and heat/phonons (R)
for nuclear recoils: Q/R allows discrimination between
nuclear recoil and electron recoil
Exist in a variety of permutations:
• Two detector types (BLIPs and ZIPs)
• Two sites: SUF(shallow), Soudan (deep)
• Two materials (Germanium and Silicon)
August 21, 2002
KITP NCCO - Harry Nelson
UCSB
7
CDMS II
CDMS Sites
Stanford Site:
• 16 mwe
• Substantial neutron flux
• Results
scintillator
veto
polyethylene
outer moderator
outer Pb shield
detectors
August 21, 2002
Icebox
inner Pb
shield
Soudan Site:
• 2100 mwe
• Neutron flux down 1/300
• Commissioning fridge
dilution
• Operation this winter
refrigerator
KITP NCCO - Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
8
4
CDMS
UCSB
CDMS II
CDMS Detectors
`BLIPs’ (Berkeley Large Ionization and Phonons)
• Germanium (1/6 kg) disks
• Heat/Phonons (R) - Thermistor
slow - wait for thermalization
• Results - 3 of 4 detectors Ionization (Q) drifted to
electrodes by applied E for
`ZIPs’ (Z, Ionization and Phonons)
both (1/10 kg) disks
• Germanium (1/4 kg) and Silicon
• R - detect athermal phonons
`TES’ - Transition Edge Sensor
Fast Signal
x, y, and… z (with risetime)
• Performance at Stanford - results very soon (4 Ge, 2 Si)
• 42 of these to be deployed at Soudan (CDMS II)
August 21, 2002
9
KITP NCCO - Harry Nelson
UCSB
CDMS II
astro-ph/0203500
August 21, 2002
KITP NCCO - Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
10
5
CDMS
UCSB
CDMS II
BLIP
R
Q Outer
Electrode
Q Inner
Electrode
R
Q
2/2000 result: Q Inner Only
8/2002 result: QI + Shared… `QIS’
August 21, 2002
KITP NCCO - Harry Nelson
UCSB
CDMS II
BLIP Calibration
1334 Photons (external source)
11
External Electrons
Q/R
233 Electrons
(tagged contamination)
616 Neutrons (external source)
August 21, 2002
Q collection incomplete
because ionization all a
few microns from surface
10 KeV Recoil Energy
KITP NCCOThreshold
- Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
12
6
CDMS
UCSB
BLIP Calibration
CDMS II
No Pulses in Veto Shield,
Electron Recoils
Mostly internal
U/Th Contamination
Q/R Discrimination: 1/1000
Suppression
August 21, 2002
13
KITP NCCO - Harry Nelson
UCSB
CDMS II
BLIP Calibration
Pulses in Veto Shield (not WIMPS),
Nuclear Recoils (from neutrons)
Inner + Shared Electrodes
Dashed Lines: MC
Inner Electrode Only
August 21, 2002
Neutron Background Well
Modeled
KITP NCCO - Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
14
7
CDMS
UCSB
CDMS II
Neutrons - signal several convolutions
down from production
August 21, 2002
15
KITP NCCO - Harry Nelson
UCSB
CDMS II
BLIP Data: Veto Clean (WIMP Candidates)
Inner: 12 kg-d
Inner Ionization
Electrode
13 nuclear recoils
Outer Ionization
Electrode
Shared: 4.4 kg-d
Shallow:
Neutrons
August 21, 2002
10 nuclear recoils
KITP NCCO - Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
16
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CDMS
UCSB
CDMS II
Neutron Checks
Multiple Hits in the 4 Ge Detectors
Short run with prototype Silicon ZIP
August 21, 2002
KITP NCCO - Harry Nelson
UCSB
17
CDMS II
Updated Limits
Shared Electrode
With WIMPs
Various Masses
Neutron Bkgd
August 21, 2002
KITP NCCO - Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
18
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CDMS
UCSB
CDMS II
Explanation, Edelweiss
Detectors: similar to CDMS
CDMS: shift toward expected
(old had high [`lucky’] neutron estim.)
Exp. CDMS
(dotted)
New CDMS
Old CDMS
2002
Edelweiss !
15.8 kg-d / 16 mwe depth
August 21, 2002
0.2% CL for consistency with DAMA
11.7 kg-d / 4500 mwe
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KITP NCCO - Harry Nelson
UCSB
CDMS II
CDMS Status
• At Shallow Site (16 mwe):
⇒ Neutron Shielding Added (reduce neutrons to 1/2)
⇒ Detector Technology Completely Changed
→ `ZIP’… detect athermal phonons
→ Pulse faster - microseconds
→ Pulse Risetime - rejection of external electrons
⇒ 4 Ge Detectors, 2 Si Detectors
⇒ 27 kg-d accumulated
→ Data Terrific
→ Results Later This Year
• Move to Soudan (2100 mwe) ASAP (42 det. Over 3 yrs.)
August 21, 2002
KITP NCCO - Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
20
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CDMS
UCSB
CDMS II
ZIP Detection Mechanism
Recoil - THz phonons
Phonons go to surface SC AlAl Al Collector
fins, break Cooper pairs, giving
qp diffusion
quasiparticles.
Quasiparticles diffuse in ~ µs to
W transition-edge sensors (TES),
where they release their energy to
the W electrons
Release energy, T is raised, R is Electro- R
Thermal
raised
Current change is measured with Feedback
SQUIDs
August 21, 2002
qp-trap
W TES
W
Si or Ge
T
21
KITP NCCO - Harry Nelson
UCSB
CDMS II
ZIPs on Germanium
1 µm
R (4 segments)
Q
August 21, 2002
R Risetime gives
Z
KITP NCCO - Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
22
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CDMS
UCSB
CDMS II
Risetime Discrimination
Nuclear recoils
(from neutron source)
surface bulk
γ
August 21, 2002
External electrons
KITP NCCO - Harry Nelson
UCSB
23
CDMS II
Recent ZIP Data
With Activity in
Veto
µ = 10.4 keV
σ = 0.34 keV
August 21, 2002
KITP NCCO - Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
24
12
CDMS
UCSB
CDMS II
Next Step: Get to Soudan, suppress neutrons
10
-38
Excluded Region (Scalar)
10
10
10
NaI UK
Ge Diode
NaI Rome
CDMS - Feb 00
EDELWEISS -June 01
-39
-40
CDMS II
-41
DAMA 3 σ claim->
10
10
10
10
CDMS Soudan
-42
MSS models
-43
-44
-45 000317
0
10
0.01 evt./kg/day
(MT)eff=230kg.day˚
CaWO 4 CRESST II
Genius
10
1
10
2
2
10
3
10
4
WIMP Mass [GeV/c ]
August 21, 2002
KITP NCCO - Harry Nelson
UCSB
25
CDMS II
Direct DM Detector
It’s probably the neutralino. We
νN)...
have g-2, A0bfb, sin2θW(ν
August 21, 2002
KITP NCCO - Harry Nelson
Harry Nelson , UCSB (KITP New Cosmology Conference 8/21/02)
26
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