Searches for Dark Matter
(the Quest)
Harry Nelson
UCSB
2003 SLAC Summer Insitute
Aug. 5-6 2003
HNN
UCSB
Recap - Direct Detection
How to dredge the small (0.01 DRU= ev/(kg d keV))
up out of a bigger background (1 DRU typical) of
recoil electrons from comptons?
• Shield (shield radioactive too!)… 1 ev/(kg d keV) typical 
• Reduce the background… HDMS , IGEX , Genius 
• Exploit astron. propert. (year cycle, directionality) DAMA, DRIFT 
• Devise detectors that can distinguish nuclear recoil from electron
recoil… Edelweiss, CDMS, Xenon..
Indirect Detection
(milli-) Charged Massive Particles
Closing
8/6/03
SLAC Summer Institute
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HNN
UCSB
Annual Modulation in Rate
• `Usual Simplification’: Halo particles are at rest, on average 2 1/2
vDM =0 km/s
• Sun moves through Halo - `apparent’ wind
• Earth modulates `wind’ velocity yearly
vk = 15 km/s
vDM1/2  300 km/s
2
Fig. from DRIFT
DAMA at Gran Sasso
Peak-to-peak up to 40%
8/6/03
SLAC Summer Institute
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HNN
UCSB
Daily Modulation in Direction
• Recoiling Nucleus Follows the Initial WIMP Direction… the `wind’
• Detector gaseous to
reconstruct recoil direction
• DRIFT at Boulby
(Spooner)
Fig. from DRIFT
8/6/03
SLAC Summer Institute
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UCSB
Copper
NaI
Lead
PMT
DAMA – 100 kg of NaI
PMT
HNN
Poly
Sodium, A=23
Eobs(KeVee)0.25 Erecoil (KeV)
Erecoil  Light
Iodine, A=127
Eobs(KeVee)0.09 Erecoil (KeV)
8/6/03
SLAC Summer Institute
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HNN
UCSB
DAMA Background and Signal
0.01950.031
-0.00010.019
cpd/kg/keV
Energy Spectrum
Bkgd  1 cpd/kg/keV
2-6 KeV
8-24 KeV Na(23)
20-70 KeV I(127)
through
through2000
2003…
…4
6.3 
Bernabei et al., astro-ph/0307403
8/6/03
SLAC Summer Institute
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HNN
UCSB
DAMA
noise...
>1 pe threshold
<10-4 cpd...
8/6/03
SLAC Summer Institute
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HNN
UCSB
DAMA Allowed Regions
p (cm2), =0 /
through 2000
10-44
Na
(standard halo)
through 2003
3
10-42
I
4
• Variation mainly due to changes in halo parameters
• two plots not directly comparable (different halos used)
• With new result, DAMA ceases to employ `standard
Maxwellian halo’ - comparisons challenging
8/6/03
SLAC Summer Institute
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HNN
Halo Variation
UCSB
Kamionkowski and Kinkhabwala (1997)
8/6/03
SLAC Summer Institute
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HNN
UCSB
Perhaps WIMP couples not to nucleons,
S,V,T,A,P  S,A non-relativistic (V too)
but to their spin
S - `nucleon, SI’ (or V) … A - `spin or SD’
A2  2 J(J+1)
J0  unpaired nucleon, odd A
(also, could break isospin… np)
p (cm2)
Couple to neutron spin
10-34
10-36
NAIAD (Boulby)
(couple to proton spin)
DAMA
LIBRA 250kg, NAIAD continues, ANAIS in Spain...
8/6/03
SLAC Summer Institute
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HNN
Discrimination of Recoils
Signal
Background
Nucleus
Recoils
Electron
Recoils
Er
v/c  710-4
Dense Energy Deposition
v/c small; Bragg
0

8/6/03
UCSB

Er
v/c  0.3
Sparse Energy Deposition
Differences the
Basis of Discrimination
SLAC Summer Institute
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HNN
UCSB
Simulation (by DRIFT)
13 keV e- in 1/20 atm Ar
40 keV Ar in 1/20 atm Ar
Ar pushes other Ar atoms,
none go very far.
Electron pushes other
electrons, all go far
5 cm
8/6/03
SLAC Summer Institute
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HNN
UCSB
dE/dx for different recoils
http://www.srim.org/SRIM/SRIM2003.htm
Strategies
Detector insensitive
to small dE/dx
(track etch, SDD)
Convert E to two
distinct measured
quantities that look
different depending
on whether nuclear
recoil or electron.
8/6/03
SLAC Summer Institute
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HNN
UCSB
Track Etch Detectors
Struck
Nucleus Corrosive Etch
Mica,
CR39
Large
dE/dx
Ancient Mica
0.5109 yr
Exposure
fraction mm2
area
100 Å
http://moedal.web.cern.ch/moedal/moedal_track.htm
8/6/03
SLAC Summer Institute
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HNN
UCSB
Mica Result
Snoden-Ifft, Freeman, Price (1994)
58% 16O
16% 28Si
12% 27Al
5% 39K
p (cm2) 10-37cm2
SD: 10-33cm2
8/6/03
SLAC Summer Institute
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HNN
UCSB
Superheated Droplet Detector (SDD)
Target, C2ClF5 (Liquid): Temp. > Boiling
Gelatin
15 gm
10 m
Collar et al., (2000)
8/6/03
0
10-36 cm2
Spin Dependent
SLAC Summer Institute
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HNN
Lose the Gelatin… get all Target
UCSB
Really a bubble chamber...
CF3Br
Juan Collar
and
Andrew Sonnenschein
(poster session)
8/6/03
SLAC Summer Institute
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HNN
UCSB
Distinct Quantities to Measure
1) Time Structure of the Pulse
2) Pulse Height/Area via:
a) Ionization (like Ge)
b) Scintillation (like NaI)
c) Heat/Phonons
d) Physical Size of Ionization
Liquid Xenon
Also a scintillator
1
10-20keV
(50-100 keV ER)
0.1
(Spooner)
0.01
e- recoils from ’s
0.001
0.0001
NaI
0.00001
1
NaI
10
100
pulse time constant (ns)
1
’s
Nuclear recoils
From neutrons
0.1
DAMA does
not use this
0.01
0.001
ER:
130-150 KeV (I)
t
0.0001
0.00001
1
1
Gerbier et al., 1998
8/6/03
Width of pulse
SLAC Summer Institute
10
10
pulse time constant ns
t (ns)
100
100
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HNN
UCSB
Distinguishing Nuclear Recoil

Nuclear recoil energy lost
mainly to collisions with other
nuclei


to electrons
8/6/03
Nuclear recoils deposit lots of
energy in lattice excitations:
phonons... heat
Nuclear motion poor at
causing electronic excitation,
ionization
to electrons
SLAC Summer Institute
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HNN
UCSB
Simultaneous Measurement of Phonons(Heat) + Ionization
Edelweiss

Temperature-20 mK

E



D(Temp)NTD Ge


D(Temp)/D(Energy)
Slow (10’s ms)
Ionization - E applied
Background (e- from ) … strong ionization
signal… equal phonon signal (!)
Nuclear recoil… reduced (by 1/4) ionization
signal, strong phonon signal
8/6/03
SLAC Summer Institute
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HNN
UCSB
Separation of Nuclear Recoil from e- Recoil
Nuclear recoils
(induced by a neutron source)
Electron recoils
(induced by a  source)
Slope really 1!
Ionization
=1
(bkgd)
1/3
(sig)
Phonons
Egap = 3/4 eV
w = 3 eV
Shutt et al., 1992
8/6/03
SLAC Summer Institute
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HNN
UCSB
Edelweiss (depth: 4500 mwe)
0.32 kg/ Ge detector
L. Chabert,
EPS `03 Aachen
8/6/03
Roman Lead
3×0.32kg
Germanium
Detectors
SLAC Summer Institute
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HNN
Edelweiss Data: ’s Suppressed by 1000
Bolometer 1
Bolometer 2


7.51 kg.d exposure
(fiducial volume)
● Best charg.
channel :
1 keV (FWHM)
● 20 keV
threshold
L. Chabert,
●
EPS `03 Aachen
8/6/03
UCSB
Bolometer 3

● 10.86 kg.d (fiducial)
3.72 kg.d
● Good phonon channel
(fiduc.)
300 eV (FWHM)
● Smaller
resolution during most
exposure due to
of the runs
electronics
● Noisy charge channel
problems
● 30 keV threshold
● 30 keV
threshold
23
SLAC Summer Institute
●
HNN
UCSB
Betas...
External 
z
GermaniumElectrode
Implants
Ionization electrons
get trapped in this
electrode

E
Those electrons never drift over to the
other electrode… ionization signal
reduced… but, all the phonons/heat still
present… (ionization)/(phonons) < 1
CDMS effort: measure z
8/6/03
SLAC Summer Institute
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HNN
Edelweiss and other’s results
UCSB
CDMS no background
subtraction hepex/0306001
28 kg-days
CDMS
with (Ge,
background
phonon/ion.)
subtraction hepex/0306001
28 kg-days (Ge,
ZEPLIN I (preliminary)
phonon/ion.)
230 kg-days (Liq Xe)
DAMA/Edelweiss
inconsistent at 99.9%...
... not accounting for
differential systematics
EDELWEISS 2003
no background subtraction
31 kg-days (Ge, phonon/ion
L. Chabert,
EPS `03 Aachen
8/6/03
SLAC Summer Institute
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HNN
CDMS: not as deep… neutron background
UCSB
17 mwe


Active Muon Veto
Pb Shield
n
Copper
n
Fridge
Polyethylene
Detectors
Inner Pb shield
... Experiment moved to Soudan,
2100 mwe depth
R. Schnee
8/6/03
SLAC Summer Institute
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HNN
UCSB
CDMS Layout, Data
FET cards
1/5000 ’s misid’ed
as nuclear recoils
SQUID cards
4K
0.6 K
0.06 K
0.02 K
ZIP 1 (Ge)
ZIP 2 (Ge)
ZIP 3 (Ge)
ZIP 4 (Si)
ZIP 5 (Ge)
ZIP 6 (Si)
8 cm
4 Germanium Detectors (0.66 kg
total)
2 Silicon Detectors (0.2 kg total)
 Small DM rate, high neutron rate R. Schnee
8/6/03
SLAC Summer Institute
Surface electrons
 Z1 () or Z5 (+)
Nuclear Recoils
27
HNN
UCSB
Technology of `ZIP’s (Z for z)
Very different from Edelweiss, although the objective
is the same… the `phono-cathode’
quasiparticle
trap
W
quasiparticle
Transition-Edge
diffusion
Sensor (TES)
Al Collector
Cooper Pair
Al
Si or Ge
phonons
~ 10mK
R. Schnee
8/6/03
RTES ()
• Signal much faster microseconds
• 3-d imaging (Z)
normal
4
3
2
1
superconducting
SLAC Summer Institute
Tc ~ 80mK
T (mK)
28
HNN
UCSB
The ZIP Phono`cathode’...
1  tungsten
380 x 60 aluminum fins
• 4 segments + timing to get x,y on the face
• rise time to get z, into the face
R. Schnee
8/6/03
SLAC Summer Institute
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HNN
ZIP Surface
Electron
Rejection
UCSB
(Single-scatter)
Neutrons Surfaceelectron recoils photons from
from
(selected via nearest- 60Co Source
252Cf
neighbor multiple
source
scatters from 60Co
source)
Accept
Surface electrons
still likely to be the
limiting background
Reject
R. Schnee
8/6/03
SLAC Summer Institute
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HNN
CDMS Expected Background Levels
UCSB
In DRU, ev/kg/kev/day
0.00014
0.0005
a bit dated;  now
X10 better, surface
electron X2 better
0.00074
0.0024
CDMS-II Proposal
8/6/03
SLAC Summer Institute
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HNN
UCSB
Catalog of Recoil Experiments
Rick Gaitskell
8/6/03
SLAC Summer Institute
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HNN
UCSB
Rick Gaitskell
Future Performances
8/6/03
SLAC Summer Institute
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HNN
Prognostication
8/6/03
SLAC Summer Institute
UCSB
34
HNN
A Proposal… 5 billion years ago…
UCSB
(indirect DM detection)
Get 1057 protons in a sphere
(ignite to enable a neutrino program)
Wait for WIMPs to collect
(spin-dependent cross section - proton’s spin)
Detect on a nearby iron ball via the annihilation
of WIMPs (with themselves) to neutrinos
Review Panel’s Recommendations/Queries:
1)What if WIMP’s don’t self annihilate… no answer
2) Hey, you’re `iron ball’ is great for collecting
WIMPS via spin-independent scattering, since
A of Iron is big (54)! (thanks)
3) Funding for preliminary studies...
8/6/03
SLAC Summer Institute

35
HNN
UCSB
Study Results...
For SUSY WIMPs… 1) Sun, rate bottleneck is capture not annihilation
2) Earth, situation reversed
3) `Relative Efficiency’ function of WIMP mass
Earth… best when
WIMP mass same as
Iron mass… same
reason hydrogen is the
best neutron moderator
lower masses…
little capture
8/6/03
Sun
SLAC Summer Institute
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HNN
UCSB
Solar/Earth Comparison
(for detector on Earth)
(WIMP models for
spin/scalar comparison)
8/6/03
Annihilation Rate in Earth
is Earth Bottleneck
Capture Rate in Earth is
Earth Bottlneck
SLAC Summer Institute
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HNN
Super-Kamiokande’s Results...
UCSB
Upward going muons
Desai, IDM 02
8/6/03
SLAC Summer Institute
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HNN
UCSB
Transcribe to the Direct Detection Plot
Model dependent… but less so than I thought.
Spin-dependent (Sun)
Scalar (Earth)
Desai, IDM 02
8/6/03
SLAC Summer Institute
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HNN
UCSB
Future Indirect Detectors (neutrino)
Feng, Matchev, Wilczek 2000
8/6/03
SLAC Summer Institute
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HNN
UCSB
Cosmic Positrons - Halo WIMP annililation
HEAT… terrific balloon experiment… saw an excess
Edsjo, IDM 02
8/6/03
SLAC Summer Institute
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HNN
Positron Future… ’s too
UCSB
Feng, Matchev, Wilczek 2000
8/6/03
SLAC Summer Institute
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HNN
1021
1018
UCSB
Milli-CHAMP Limits
1015
1012
Excluded Regions
m (GeV)
109
106
103
Overclose Universe
(Thermal)
1
10-3
10-6
10-9
8/6/03
Davidson, Hannestad, Raffelt, hep-ph/0001179
SLAC Summer Institute Charge Fraction
43
HNN
UCSB
Stable CHAMPs in Matter
DM, stop in earth
Perl et al., hep-ph/0102033
8/6/03
SLAC Summer Institute
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HNN
UCSB
Some conclusions

Rutherford/Chadwick hunted neutron for 12 years


Neutrino studies started about 90 years ago…


Hints first seen on continent, interpreted as photons…
Masses? Majorana? Still not fully nailed down...
Dark Matter…
Prepare for a long ride… no physical law guarantees
that discoveries happen within any human’s lifetime
 The only guarantee: if we fail to look, we will fail to
find.

8/6/03
SLAC Summer Institute
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