Searches for Dark Matter (the Quest) Harry Nelson UCSB 2003 SLAC Summer Insitute Aug. 5-6 2003
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Transcript Searches for Dark Matter (the Quest) Harry Nelson UCSB 2003 SLAC Summer Insitute Aug. 5-6 2003
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
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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
vDM1/2 300 km/s
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Fig. from DRIFT
DAMA at Gran Sasso
Peak-to-peak up to 40%
8/6/03
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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
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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
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HNN
UCSB
DAMA Background and Signal
0.01950.031
-0.00010.019
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
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HNN
UCSB
DAMA
noise...
>1 pe threshold
<10-4 cpd...
8/6/03
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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
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Halo Variation
UCSB
Kamionkowski and Kinkhabwala (1997)
8/6/03
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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)
J0 unpaired nucleon, odd A
(also, could break isospin… np)
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
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Discrimination of Recoils
Signal
Background
Nucleus
Recoils
Electron
Recoils
Er
v/c 710-4
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
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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
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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
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HNN
UCSB
Track Etch Detectors
Struck
Nucleus Corrosive Etch
Mica,
CR39
Large
dE/dx
Ancient Mica
0.5109 yr
Exposure
fraction mm2
area
100 Å
http://moedal.web.cern.ch/moedal/moedal_track.htm
8/6/03
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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
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Lose the Gelatin… get all Target
UCSB
Really a bubble chamber...
CF3Br
Juan Collar
and
Andrew Sonnenschein
(poster session)
8/6/03
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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
0.1
(Spooner)
0.01
e- recoils from ’s
0.001
0.0001
NaI
0.00001
1
NaI
10-20keV
(50-100 keV ER)
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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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
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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
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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
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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UCSB
Catalog of Recoil Experiments
Rick Gaitskell
8/6/03
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UCSB
Rick Gaitskell
Future Performances
8/6/03
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Prognostication
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UCSB
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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
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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
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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
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Super-Kamiokande’s Results...
UCSB
Upward going muons
Desai, IDM 02
8/6/03
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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
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UCSB
Future Indirect Detectors (neutrino)
Feng, Matchev, Wilczek 2000
8/6/03
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UCSB
Cosmic Positrons - Halo WIMP annililation
HEAT… terrific balloon experiment… saw an excess
Edsjo, IDM 02
8/6/03
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Positron Future… ’s too
UCSB
Feng, Matchev, Wilczek 2000
8/6/03
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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
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UCSB
Stable CHAMPs in Matter
DM, stop in earth
Perl et al., hep-ph/0102033
8/6/03
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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.
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