the search for dark matter the cryogenic dark matter search (cdms)
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The Search for Dark Matter The Cryogenic Dark Matter Search (CDMS). A Personal Account Roger Dixon. Outline. What is dark matter and why search for it? Detection Techniques Some Results DAMA-- Yes CDMS-- No Undergraduate Student Participation. Case Western Reserve University - PowerPoint PPT PresentationTRANSCRIPT
The Search for Dark MatterThe Cryogenic Dark Matter Search (CDMS)
A Personal Account
Roger Dixon
Dak Matter 10-26-01R. Dixon
Outline
• What is dark matter and why search for it?• Detection Techniques• Some Results
– DAMA-- Yes
– CDMS-- No
• Undergraduate Student Participation
Dak Matter 10-26-01R. Dixon
Cryogenic Dark Matter Search Collaboration
Case Western Reserve UniversityD.S. Akerib, A. Bolozdynya,
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 LabE.E. Haller, R.J. McDonald,
R.R. Ross, A. Smith
Nat’l Institute of Standards & Tech.J. Martinis
Princeton UniversityT. Shutt
Santa Clara UniversityB.A. Young
Stanford UniversityD. Abrams, L. Baudis, P.L. Brink, B. Cabrera, C. Chang, R.M. Clarke,
P. Colling, A.K. Davies, T. Saab
University of California, BerkeleyS. Armel, S.R. Golwala, J. Hellmig, V. Mandic, P. Meunier, M. Perillo Isaac, W. Rau, B. Sadoulet, A.L. Spadafora
University of California, Santa BarbaraD.A. Bauer, R. Bunker,
D.O. Caldwell, C. Maloney,
H. Nelson, J. Sander,
A.H. Sonnenschein, S. Yellin
University of Colorado at DenverM. E. Huber
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CDMS II
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Rotation Curve of Solar System
10000
20000
30000
40000
50000
Distance from the Sun (Meters x 1012)
1 2 3 4 5 6
PlutoUranus
Saturn
Jupiter
Mars
Earth
Venus
Mercury
Neptune
Prediction for dust filled solar system (no sun)
Newtonian prediction for sun alone (no dust)
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Rotation Curve of Our Galaxy
Satellite Galaxies
GC
MC
GC
CO
GC
300
40
200
100
806020
Newtonian Prdiction
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Rotations Curves
Edge of Luminous Disk
Newtonian Prediction
Vel
ocit
y km
/sec
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Big Bang Nucleosynthesis
• BBN predicts relative abundance of hydrogen, deuterium, helium, and lithium
• Measurement of these abundances
Ωbaryon ≤ .05
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Inventory of the Universe• Visible Matter .01
– Evidence
• Telescope observations
– Composition
• Ordinary matter-- protons and neutrons
• Baryonic Dark Matter .05– Evidence
• BBN
– Composition
• Matter too dim to see
• Nonbaryonic Dark Matter .3– Evidence
• Gravity, CMB
– Composition
• WIMPs, Axions, Neutrinos
• Cosmological Dark Matter .6– Evidence
• CMB, Supernova Data
• Total ~1
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Energy Distribution of Dark Matter
GM =v2r
v tot(r) = vd2 (r) +vh
2 (r)[ ]12
ρ r( ) =1
4πGr 2
d
drrvh
2 r( )( )
ρ0 = .3 → .6 GeV • cm−3
v tot(r) ≈200 km⋅sec−1
v21
2 ≈270 km• sec−1
By using information from the Rotation Curves we get
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Candidates
• Machos
• Particle physics points the way– Supersymmetry (neutralinos)– Axions– Massive neutrinos
• Extra Dimensions, curved space, gravitational solutions and on and on . . . Wimpzillas-- people actually get paid to make this stuff up
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WIMP Direct Search Stategies
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How Much Dark Matter is in this Room?
• Rotations curves ==> .3 GeV/cm3
• Dark Matter in a cubic foot of space in this room assuming each has a mass of 50 GeV-- 170 neutralinos
• Total Dark Matter in Solar System = 4.6 X 1017 kg=260 Trillion Buicks
• Mass of Sun = 2 X 1030 kg• E = MC2 in Sun ==> 4 years worth of Buicks
Dak Matter 10-26-01R. Dixon
WIMPs in the Galactic Halo
If WIMPs were produced in the early universe, today they would reside in the halo of the galaxy. An earth-based detector traveling through this halo could detect the particles when they occasionally undergo ‘billiard-ball’ collisions with atomic nuclei.
The energy transferred to the scattered nucleus appears as signals in the detector – but how to be certain the signal is due to a WIMP and not some other ordinary ‘background’ particle? In the CDMS experiment, the detectors make all the difference.
halo
bulge
disksun
The Milky Way
WIMP detector
energy transferred appears in ‘wake’ of recoiling nucleus
WIMP-Nucleus Scattering
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Ge BLIP Ionization & Phonon Detectors
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BLIP TEST DATA
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Test Particles
Detector performance measured with radioactive sources under laboratory conditions
Electron recoils induced from a gamma (photon) source to simulate background eventsNuclear recoils induced from a neutron source to simulate WIMP events
Clean separation provides rejection of background events due to photons and electrons.
(Cha
rge
Yiel
d)
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Stanford Site, Shield, and Cryostat
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The CDMS Experiment
polyethyleneouter moderator
detectors inner Pbshield
dilutionrefrigerator
Iceboxouter Pb shieldscintillator
veto
60 m
m
170 gram Ge
60 mm
Stack of germanium detectorsThe thermal measurement requires that the detectors be ultra-cold. They are maintained at a temperature of 10 milli-Kelvin by a dilution refrigerator. Because the rate for WIMP scattering is so low, the experiment must also be carefully designed for background suppression: high-purity materials with low radioactivity, shielding against external radiation, an underground site to reduce the flux of cosmic radiation, and a veto to detect residual cosmic rays.
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Icebox and Shielding
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CDMS Data 1999
The detectors were exposed for a period of several months. The blue dots are the data that remain after rejecting events in coincidence with the cosmic-ray veto or a second detector (see next panel). The circled events are those that fall in the nuclear-recoil band and could be due to WIMPs. However, we also expect nuclear recoils from neutrons that were produced by un-vetoed cosmic rays. These must be estimated and subtracted off to extract the rate due to WIMPs.
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Neutron Subtraction: Single Scatters vs Multiple Scatters
Single-scatter nuclear-recoils are produced by WIMPs or neutrons.
Multiple-scatter nuclear-recoils are only produced by neutrons.
In addition to the 13 single-scatters, 4 multiple-scatters are observed. The multiple-scatters are used to estimate how many of the single-scatters are due to neutrons. After neutron subtraction, the results are consistent with no single-scatters due to WIMPs.
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Limits on WIMP Cross-sectionsTo quantify our non-detection of
WIMPs for comparison with other experiments and theoretical predictions, a statistical analysis is performed. For each possible WIMP mass, we determine the largest WIMP size* that could have gone undetected in the data. The regions above the U-shaped curves are ruled out by various techniques.
The shaded/dotted regions are predictions from particle physics theories.
CDMS 1999
DAMA 3DAMA 2
DAMA 1996
Ge ioniza
tion
Theory
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Annual Modulation
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Interesting Times…CDMS after background subtraction
The DAMA Collaboration runs a competing experiment using a different technique. They look for a seasonal variation in rate expected for WIMPS caused by the Earth’s orbit around the Sun. The amplitude of the modulation correlates with the WIMP-nucleon cross section (effective size).
The best simultaneous fit is shown in red. It corresponds to a WIMP-nucleon cross section too small to explain DAMA’s amplitude but too large to go unseen in CDMS.
DAMA 4 year data set
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Looking Ahead
The next step for CDMS– Larger array & longer exposure– Second generation detectors
with event positions– Deeper site for further reduction
in cosmic-ray background
Soudan Mine, Northern Minnesota
2300’ depth
CDMS IISoudan II
MINOS
DAMA 100kg NaI
CDMS Soudan
CDMS Stanford
Genius Ge 100kg 12 m tank
CDMS (Latest)
CRESST
Sensitivity goals of future experiments
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W/Al QET Sensors
CAB
D
n,γ Eph + Ee-h(WIMPS)
20mKbase
100 g Si and 250 g Ge Crystals
1 cm Thick X 3” Dia
Qinner
Qouter
Vqbias
-30 -20 -10 0 10 20 30 40 50 60 70-100
0
100
200
300
400
500
600
700Ionization and Phonon Event in 100 g Si Detector
Time [µsec]
Ionizationsignal defines
start time
Signals fromthree of fourphonon sensors(largest signalarrives first,etc)
τ ph−Ge ~4τ ph− Si ~220 μs
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Transition Edge Sensors• Steep Resistive Superconducting Transition
• Voltage bias is intrinsically stable
R
T
• W Tc ~ 70-90 mK• 10-90% <1 mK
α =dR
dT
R
Tunitless measure
of transition width
Rshunt
Ibias
W ETF-TES
SQUIDArray
The Joule heating produced by bias
PJ =VB
2
R⇒ PJ ↓ whenR↑
is stable whereas for current bias
PJ =I B2 R ⇒ PJ ↑ whenR↑
which is intrinsically unstable
Dak Matter 10-26-01R. Dixon
Detector FabricationAl/W Grid
60% Area Coverage
37 - 5 mmSquares 888 X 1 µm
tungsten TESin parallel
Aluminum Collector Fins
8 Traps
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BLIP TEST DATA
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Surface Electrons
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Rise Time Cuts
Gammas (high Q/P),neutrons shifted slitghtly
higher
Electrons (low Q/P)
beta/neutron discrimination
better than 20:1
(a) Mu-coincident
with RT cutMu-anitcoin
without RT cut
(b) Mu-coincident
with RT cutMu-anitcoinwith RT cut
Dak Matter 10-26-01R. Dixon
Rise Time Descrimination
Beta source events
gamma calibration
nuclearrecoils
slowrisetime
fastrisetime
nuclearrecoils
gammas
gammas
betas betas
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CDMS II
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CDMS Shield
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Undergraduate Participation
• Internships for Physics Majors– http://ipm.fnal.gov/– Wide Participation– But, only about 20 students
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Students and Activities on CDMS• Jamie Lush, University of South Dakota (1997)
– Worked on software for testing electronics and power supplies
• Steven Furlanetto, Carlton College
– Simulation software
• Theodossis Trypiniotis, Cambridge (1999)– Simulations
• Shahin Rahman, Washington University (2000)– CDMS/DAMA Cross-section calculations
• CDMS/DAMA Problem (2000)
– Daniel Osborn, Harvey Mudd
– Priscilla Payan, UCLA
– Ingyin Zaw, Havard
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Conclusions
• “If you want to find dark matter, why don’t you just go outside at night?”
Sam Dixon
Mineral Hill, NM