Dark Matter Overview
Harry Nelson
UCSB
INPAC
Oct. 4, 2003
HNN
UCSB
Outline


Axions
Massive Particles

Direct Detection
 Weakly
Interacting
 No Strongly Interacting (interesting opportunities)

See talks of Dave Cline (ZEPLIN), Patrizia
Meunier (CDMS-II)
10/4/03
INPAC
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HNN
UCSB
Usual Simplifications of Dark Matter

Local energy density, 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.

10/4/03
INPAC
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HNN
UCSB
Advice of Dennis the Menace
10/4/03
INPAC
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HNN
Usual Simplifications of Dark Matter


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:
10/4/03
vDM=0 (sun plowing through at v0  220 km/s)
2 1/2  300 km/s… useful to approximate  0
vDM
INPAC
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HNN
UCSB
Round up the Usual Suspects

e,m,t e-
0
p
n
-- Our Matter
0 (SUSY, neutralino, WIMP)
a axion, couples to … nonthermal, very light
10/4/03
INPAC
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HNN
UCSB
Direct Detection

Momentum Transfer
v0
Convert a to photon – detect it
axion
m
v0
target
Massive
Particle
Cause target recoil – detect it
10/4/03
INPAC
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HNN
UCSB
Axions (and similar)
axion models
(Dark matter)
1.9-3.4 meV (ADMX, LLNL-Florida-Berkeley-NRAO)
10/4/03
INPAC
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HNN
UCSB
Primakoff Conversion, Microwave Detection
Amplifier – power pours out
of cavity when B0 applied
Lower noise allows faster
scanning….
Solenoid
LB= 50 cm
Cavity, `TM’ mode
(E parallel to B0: 0- )
10/4/03
INPAC
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HNN
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
10/4/03
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HNN
UCSB
Nuclear Recoil – Cross Section
A4
10/4/03
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HNN
UCSB
WIMP Region
Large Exposure, Background:
DAMA (58K kg-days, NaI)
ZEPLIN (230 kg-days, Xe)
IGEX (276 kg-days, Ge Ioniz)
Small Exposure, Background:
CDMS (28 kg-days, Ge P/I)
Edelweiss (12 kg-days, Ge P/I)
(DRIFT - gaseous, recoil dir.)
10/4/03
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HNN
UCSB
Event Rates...
Xe Nuclear Form Factor
~ several 10-2 ev/kg/d/keV
Rick
Gaitskell
10/4/03
INPAC
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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 (Ge Ionization)
• Exploit astron. properties (year cycle, directionality) DAMA, DRIFT
• Devise detectors that can distinguish nuclear recoil from electron
recoil… Edelweiss, CDMS, Xenon..
10/4/03
INPAC
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HNN
UCSB
DAMA: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%
10/4/03
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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
10/4/03
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HNN
UCSB
DAMA
noise...
>1 pe threshold
<10-4 cpd...
10/4/03
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HNN
UCSB
DAMA Allowed Regions
p (cm2), =0 /
through 2000
10-44
through 2003
(standard halo)
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
10/4/03
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HNN
UCSB
DAMA vs. Super-K
Model dependent… but less so than I thought.
Spin-dependent (Sun)
Scalar (Earth)
Desai, IDM 02
10/4/03
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HNN
UCSB
Discrimination of Recoils
Signal
Background
Nucleus
Recoils
Electron
Recoils
Er
v/c  710-4
Dense Energy Deposition
v/c small; Bragg
0


10/4/03
INPAC
Er
v/c  0.3
Sparse Energy Deposition
Differences the
Basis of Discrimination
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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
10/4/03
INPAC
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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
10/4/03
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HNN
UCSB
Edelweiss (depth: 4500 mwe)
0.32 kg/ Ge detector
L. Chabert,
EPS `03 Aachen
10/4/03
Roman Lead
3×0.32kg
Germanium
Detectors
INPAC
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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
10/4/03
Bolometer 3


3.72 kg.d
(fiduc.)
● Smaller
exposure due to
electronics
problems
● 30 keV
threshold
INPAC
●
UCSB

10.86 kg.d (fiducial)
● Good phonon channel
300 eV (FWHM)
resolution during most
of the runs
● Noisy charge channel
● 30 keV threshold
●
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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
10/4/03
INPAC
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HNN
UCSB
CDMS-II Projections
~1cal year, initial deployment
10/4/03
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HNN
UCSB
Some conclusions


Axions searches about to become much more
sensitive
WIMPs…

Next few years should get factor of 100
sensitivity
 High Mass, Bkgd versus Low Mass, Bkgd:
How
well do very high mass detectors self shield?
Can low mass, bkgd be mass produced with everlower background requirements?
Is Xe, with ionization, `middle way’?

INPAC...
10/4/03
INPAC
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