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Michael B. Crisler Fermi National Accelerator Laboratory
03 June 2003
The Cryogenic
Dark Matter Search
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CDMS CollaborationSanta Clara University
B.A. YoungStanford University
L. Baudis, P.L. Brink, B. Cabrera, J.P. Castle, C.Chang, R. M. Clarke, A.K. Davies, M.Hennessey, M. Kurylowicz, S.W. Nam, W.Ogburn, A.Perales, T. Saab, A. Tomada
University of California, BerkeleyM.S. Armel, J. Alvaro-Dean, S. Golwala,
J. Helmig, A. Lu, V. Mandic, P. Meunier,
N. Mirabolfathi, M.C. Perillo Isaac, W. Rau,
R.R. Ross, B. Sadoulet, D. Seitz, G. Smith,
A.L. Spadafora
University of California, Santa BarbaraD.A. Bauer, R. Bunker, D.O. Caldwell,R. Ferrl, R. Mahapatra, C. Maloney,H. Nelson, R. Nelson, J. Sander, C. Savage, S. Yellin
University of Colorado at DenverM. E. Huber
Case Western Reserve UniversityD.S. Akerib, A. Bolozdynya, D. Driscoll,S. Kamat, T.A. Perera, R.W. Schnee,
G.Wang
Fermi National Accelerator LaboratoryM.B. Crisler, R. Dixon, D. Holmgren,
M. Haldeman
Lawrence Berkeley National LaboratoryJ. Emes, R.J. McDonald, R.R. Ross, A. Smith
National Institute of Standards and Technology
J. Martinis
Princeton UniversityT. Shutt
Brown UniversityR.J. Gaitskell, M.J. Attisha,
J-P.F. Thompson
University of MinnesotaP. Cushman, L. Duong, A. Reisetter
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Galactic Big Picture Weakly Interacting Massive Particles
nuclear recoil~ 10’s of keV
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total = 1.02
= 0.73
M = 0.27
Latest Results from WMAP Bennett et al.
b = 0.044
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WIMP Velocity PlotHalo model provides reliable estimate of particle flux
(r) 0
a2+r02
=a2+r2
f(v) d3v =3/2 v0
3exp(v2/v0
2)d3v
1
0 = 0.3 GeV/cm3
a = 6.4 kpc
r0 = 8 kpc
v0 = 220 km/sec
7% annual modulation
Typical collision velocity ~ 320 km/sec
particle flux x = 0v/mx
Erecoil ~ ½ mN v2WIMP ~ 10’s of
keV
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Interaction Rate
from big-bang: Density x ~ 1 / interaction rate
x ~ .3 => v ~ 10-26 cm3/s
x ~ weak
x is unknown …but we can guess
scalar interaction => NUCLEUS = A2 NUCLEON
Standard assumption:
depends only on the halo model (and on mx)
particle flux x = 0v/mx
mx is unknown …but we can guesslightest superpartner? mx ~100
GeV/c2
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…Quantification of Our Ignorance
unknown mx
unknown x
Current CDMS SUF Limit
Projected Soudan Site 1 Month
Projected CDMS Soudan Limit
Your favorite SUSY models
DAMA experiment
possible signal
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Technical Challenges:
Very Small Signals
characteristic nuclear recoil energy ~ 10 keV
Very Low Count Rates
expect << 1 event /kg/day
Plenty of Background
gamma, beta, neutrons from cosmic rays, contamination, radon…
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CDMS Experimental Strategy
Simultaneous Measurement of Erecoil and QionizationSeparate Gamma and Beta interactions (most of the background) from true nuclear recoils (neutrons or WIMPs)
powerful new solid state detectors
Optimize our shielding design to minimize neutron backgrounds
Underground site
Stanford Underground Facility (35’, 17 mwe)Soudan Mine Underground Laboratory (2500’)
Other Analysis Handles for neutron rejection:Multiple scattering analysis (WIMPS don’t, neutrons do…)Two target materials Si for neutrons, Ge for WIMPs
Independent Monte Carlo Analysis of neutron flux
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CDMS Detectors
1 cm
pure Si or pure Ge solid state detectors
very cold ~ 0.01 oKDirect calorimetric measurement of Erecoilconventional measurement of ionization Qionization efficiency Q/Erecoil --> provides particle IDelectrode segmentation for position sensitivity
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Athermal Phonon Detection
localize the interaction within the crystalSpeed of sound in Si (Ge) = 1 (0.5)
cm/s
prompt phonon detection with segmented electrodes
phonons
Scattered particle
Ge crystal
Superconducting Al
tungsten sensor
phonon
Quasi-particle excitations (broken cooper pairs)
Quasiparticle Trap Assisted
Electro-Thermal Feedback
Power = V2 / R
heat
temperature
R
bias here…
Transition Edge Sensor
~80 mK
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1 m
normal resistance
superconducting
ETF-TES region
The CDMS ZIP Detectors
Q inner
Q outer
A
B
D
C
Rbias
I bias
SQUID array Phonon D
Rfeedback
Vqbias
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Phonon and Charge Pulses in Si and Ge
noise < 1 keV
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CDMS ZIP Detector: Source Calibration
ERECOIL
gammas
ioniz
ati
on
effi
cien
cy
nuclear recoils
ERECOIL
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Am241 : 14, 18, 20, 26, 60 kev
Cd109 + Al foil : 22 kev
Phonon Response … Position Sensitivity
Cd109 : 22 kevi.c. electr 63, 84 KeV
Delay Plot
A D
CB
T. Saab, Stanford U. from GSFC Talk 2002
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Phonon Rise-time … Depth Sensitivity
neutrons
surf
ace
bu
lk
gammas
n
(WIMP)
electrons
Incomplete charge collection at the surface
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1999 Data Set …3 pre-ZIP Ge DetectorsInner-Electrode Shared-Electrode
Shared-electrode
B4
B3
B5
B6
Inner-electrode
All 1998/1999 data consistent with neutrons only
, except…
23 events consistent with WIMPs
ioniz
ati
on
effi
ciency
ionization efficiency
4 double scatters…
1998 Data Set …1 Si ZIP
4 events on Si…
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CDMS I->II• Go deep underground• Athermal phonon technology
– Even better rejection of background
• Increase the mass -> 7kg– 7 towers of 6 detectors
• Approved in January 2000
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2001/2002 Data Set …full tower 4 Ge, 2 Si ZIPs
28.3 kg-days for WIMPs20 Ge nuclear-recoil candidates > 5 keV
increased polyethelene shielding reduced neutron flux by 2.3
non-neighbor double scatterstriple scatters !
Again consistent with neutrons only
2 Si events
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CDMS Sensitivity (Stanford Underground Facility)
CDMS 1998/99
DAMA
no subtractionCDMS new…
Edelweiss !
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30 feet
Stanford U. Campus
2500 feet
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Downtown Ely, Minnesota
T. Saab, Stanford U.
(shown here during rush hour…)
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Soudan Shielding Assembly
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Pb Lid in Place
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Cryo Plant in Place (CDMS WEBCAM)
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Source Calibration (CDMS WEBCAM)
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Veto Shield in Place (CDMS WEBCAM)
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CDMS Status / Summary
Beam Continues to Run Smoothly…
Expect Data this Summer
including the one used for data taking at Stanfordsystem has been cold and fully operational. One more cryo bug…
Two Full Towers of Detectors in Place at Soudan
…only 2465’ further underground
with the exact same apparatus…
Much excitement about repeating this measurement