Searches for Dark Matter
(the Quest)
Harry Nelson
UCSB
2003 SLAC Summer Insitute
Aug. 5-6 2003
HNN
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
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UCSB
Plan
Introductory Material
Axions
Massive Particles

Direct Detection

Strongly Interacting
 Weakly Interacting

Indirect Detection
 charged/milli-charged
Concluding Material
Small calculations, supporting material
interspersed… my goal is to develop a `feel’
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SLAC Summer Institute
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Some Sources…
UCSB
M. Srednicki, 1994 SLAC Summer Institute
http://www.slac.stanford.edu/pubs/confproc/ssi94/ssi94-010.html
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M. Perl et al., 2001
http://www.slac.stanford.edu/pubs/slacpubs/8000/slac-pub-8772.html
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IDM 2002 http://www.shef.ac.uk/~phys/idm2002/talks/
SPIRES http://www.slac.stanford.edu/spires/hep/
NASA Astrophysics Data System
http://adswww.harvard.edu/index.html
Apologies for figures not perfectly acknowledged…
Thanks to many colleagues…
particularly Ron Ross…
8/5/03
SLAC Summer Institute
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UCSB
The Milky Way’s Dark Halo (?)
R is the distance from center
v
v is the speed (tangential)
Honma and Sofue, 1996
R
v
220 km/s
:v0=180 km/s
Without the Dark Halo
(Binney & Tremaine)

8/5/03
SLAC Summer Institute
R
4
HNN
UCSB
The Dark Ball
Bulge
Disk
Dark Matter
`Halo’
Why haven’t dark
matter `particles’ fall
into our disk?
• Dark particles scarcely
interact with us and/or
• Dark particles very heavy
(150 passes/age of U)(0.3 to 2) 
10-2 gm/cm2  (0.5 to 3) gm/cm2 …
not very restrictive
8/5/03
SLAC Summer Institute
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UCSB
Theoretical Guidance… Caveat Emptor
1972
8/5/03
SLAC Summer Institute
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UCSB
Remainder of L. Alvarez Essay
8/5/03
SLAC Summer Institute
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Talavera … reviewed Columbus
UCSB
12,000 km (Talavera, accurate)
5,000 km (Columbus, fudged systematics)
Japan (Cipangu)
Both simplified the
intervening
region to pure ocean
Portugal/Spain
Oversimplification!
8/5/03
SLAC Summer Institute
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HNN
UCSB
Usual Simplifications of Dark Matter

Local energy density, `apparent’ speed of DM
km
MeV
v 0 ø 220
(ì 0 ø 7 â 10à 4)
ú0 ø 300
3
s
cm
(ì 20 ø 12 â 10à 6)
0? (200-2000)
(170-270)
… from galactic astrophysics
Consists of one elementary particle (!)
 , e,m,t , e- , p , n - 7 in our few percent of Univ.
2 are composite… n ??
The DM particle that provides the clearest signal in
a search might not be the most abundant – a strong
argument for an eclectic mix of search techniques.
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8/5/03
SLAC Summer Institute
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UCSB
Advice of Dennis the Menace
8/5/03
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Usual Simplifications of Dark Matter
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UCSB
DM not baryons (CBR, BBN; Eros/MACHO)
DM was once in thermal equibrium
mass > few keV (large scale structure)
mass < 340 TeV (unitarity)
cross section with us  weak (10-44-10-36 cm2)…
little unknown missing energy at LEP, Tevatron… mass>10’s GeV
Weakly Interacting Massive Particles
SUSY restored just above weak scale gives WIMPS
…Attractive candidates (axions, `*zillas’, etc.) were
never in thermal equilibrium…

DM at rest:
8/5/03
vDM=0 (sun plowing through at v0  220 km/s)
2 1/2  300 km/s… useful to approximate  0
vDM
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UCSB
Scope

Keep an open mind…

e,m,t e-
0
p
n
-- Our Matter
Imagine arbitrary (short
distance) interaction, mass
SIMP, *zilla
0 (SUSY, neutralino, WIMP)
Assume >10’s GeV
X±
(experimental technique)
`milli’ -CHAMP
a axion, couples to … nonthermal, very light
8/5/03
SLAC Summer Institute
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UCSB
Direct Detection

Momentum Transfer
v0
Convert a to photon – detect it
axion
m
v0
target
Massive
Particle
Cause target recoil – detect it
8/5/03
SLAC Summer Institute
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UCSB
Axions (and similar)
axion models
(Dark matter)
1.9-3.4 meV (ADMX, LLNL-Florida-Berkeley-NRAO)
Leslie Rosenberg
8/5/03
SLAC Summer Institute
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UCSB
Primakoff Conversion, Microwave Detection
Amplifier – power pours out
of cavity when B0 applied
LB= 50 cm
Solenoid
Cavity, `TM’ mode
(E parallel to B0: 0- )
Leslie Rosenberg
8/5/03
SLAC Summer Institute
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UCSB
Tunable Cavity
Tuning Rods
2Q
80 sec/scan
 1 year
Leslie Rosenberg
8/5/03
SLAC Summer Institute
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UCSB
Signal Level and Noise
(s/n)
10-17 W from
Pioneer 10
Spacecraft,
1010 km away
HEMT
10-26 W 
(time)
Substantial
improvements in
Ts are on the
horizon (X30)
from increased
cooling, SQUIDS
Leslie Rosenberg
8/5/03
SLAC Summer Institute
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UCSB
Example of Data, Expected Signal
Long resident
axions
Axions just
streamed in from
galactic periphery
(2 )
Leslie Rosenberg
8/5/03
SLAC Summer Institute
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meV Axion Future
UCSB
• ADMX – SQUIDs, hope to cover 2 decades in mass
• Kyoto – single quantum detector
Leslie Rosenberg
8/5/03
SLAC Summer Institute
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CAST – Axions from the Sun
UCSB
cm-2 sec-1 keV-
1
8 × 1014
6 × 1014
4 × 1014
2 × 1014
0
0
2
4
E (keV)
6
8
10
LHC Dipole
8/5/03
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UCSB
Experiment and Expected Sensitivity
SOLAX + COSME
Helium to suppress
momentum transfer
8/5/03
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UCSB
Massive Particles: Recoil Kinematics - I
2/3
8/5/03
SLAC Summer Institute
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UCSB
Recoil Kinematics - II
8/5/03
SLAC Summer Institute
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UCSB
Nuclear Recoil – Cross Section
A4
`scalar’ or SI (Spin Independent)
8/5/03
SLAC Summer Institute
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Nuclear Recoil – Diffraction
UCSB
Iodine
(A=127)
DAMA
0 110 220 330 keV ER
8/5/03
SLAC Summer Institute
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HNN
UCSB
Nuclear Recoils from Massive Dark Matter

Deposit 10’s of keV

For target atomic weight A<160, dark matter
velocity spectrum a delta-function, recoil spectrum
flat up to an endpoint

Diffraction off nucleus, form factor of nucleus
directly appear in recoil spectrum

Cross section favorable as A increases

Haven’t focused on magnitude of cross section yet…
10-44-10-36
8/5/03
cm2 (weak) or 10-24 cm2 (strong) still fine…
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UCSB
To Penetrate the Atmosphere
8/5/03
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UCSB
SIMP exclusion (above/below atmos.)
Penetrate to Earth
Wandelt et al., astro-ph/0006344
8/5/03
WIMPS
SLAC Summer Institute
Baudis & Albuquerque,
astro-ph/0301188
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UCSB
SIMP Exclusion, Oroville Experiment
Caldwell, Snowmass, 1994
8/5/03
SLAC Summer Institute
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UCSB
Guide to Exclusion Plots
T
excluded
<1 particle
penetrates
excluded:

8/5/03
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WIMP/nucleon p 10-42 cm2
UCSB
Exper.
CDMS
DAMA
Theory
SUSY,
various constraints
including Big Bang
8/5/03
SLAC Summer Institute
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HNN
UCSB
Compare with Common Background Rate
 DRU
• Shield (shield radioactive too!)… 1 ev/(kg d keV) typical
• Reduce the background… HDMS , IGEX , Genius
• Exploit astron. properties (year cycle, directionality) DAMA, DRIFT
• Devise detectors that can distinguish nuclear recoil from electron
recoil… Edelweiss, CDMS, Xenon..
8/5/03
SLAC Summer Institute
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HNN
UCSB
Germanium: Quest for Lowest Background
HDMS at Gran Sasso (3800 mwe (meters water equivalent) depth)
Inner Germanium (0.2 kg)
Outer Ge (2.1 kg) Spectrum of Inner Ge, 132.4 days
Red: No Hit in Outer Ge
0.3 DRU
8/5/03
SLAC Summer Institute
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HNN
UCSB
IGEX (2 kg Ge, CANFRANC, 2450 mwe)
1.0
BACKGROUND
4-10 keV background:
10-20 keV background:
25-40 keV background:
0.9
counts/keV/kg/day
0.8
0.7
0.22 c/keV/kg/day
0.10 c/keV/kg/day
0.04 c/keV/kg/day
0.6
Previous spectrum (236 kg-days)
0.5
IGEX-DM data since summer
2001 (194 kg-days)
Neutron shielding improved
0.4
0.3
Further increased neutron
shielding (82 kg-days)
0.2
0.1
0.0
0
10
20
30
40
50
Energy (keV)
8/5/03
SLAC Summer Institute
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HNN
UCSB
KeVee versus KeV (Recoil); Signal Shape
1.0
Only about 1/3 of energy of a nuclear
recoil appears in Ge as ionization
E. Simon et al., 2003
0.9
counts/keV/kg/day
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
0
IGEX
8/5/03
3010
30
40
6020
90
120
Energy
(keV) KeV
Recoil
Energy
(KeV)
ee
SLAC Summer Institute
50
150
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UCSB
IGEX Exclusion Region
10-39
IGEX-DM 2000
IGEX-DM
2001& 2002
-40
p (cm2)
10
-41
10
DAMA allowed
-42
10 1
8/5/03
5
10
50 100
m (GeV)
SLAC Summer Institute
5001000
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HNN
Genius Program – Background Elimination
UCSB
Suspend Ge detector
in Liquid Nitrogen
L= 2 m
0.1 events/(kg KeV d)
Genius Test Facility
(under construction)
40 kg Ge
8/5/03
Baudis et al., 2001
SLAC Summer Institute
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UCSB
Ultimate Genius
8/5/03
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