Searches for Dark Matter the Quest

1
Searches for Dark Matter(the Quest)

• Harry Nelson
• UCSB
• 2003 SLAC Summer Insitute
• Aug. 5-6 2003

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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
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Annual Modulation in Rate

• Usual Simplification Halo particles are at
  rest, on average
• Sun moves through Halo - apparent wind
• Earth modulates wind velocity yearly

Fig. from DRIFT
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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
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DAMA 100 kg of NaI
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DAMA Background and Signal
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DAMA noise...
gt1 pe threshold lt10-4 cpd...
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DAMA Allowed Regions
??p (cm2), ??0 /?
through 2003
through 2000 (standard halo)
Na
10-44
3?
10-42
4?
I

• 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

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Halo Variation
Kamionkowski and Kinkhabwala (1997)
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Perhaps WIMP couples not to nucleons, but to
their spin
S,V,T,A,P ? S,A non-relativistic (V too) S -
nucleon, SI (or V) A - spin or SD (also,
could break isospin n?p)
LIBRA 250kg, NAIAD continues, ANAIS in Spain...
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Discrimination of Recoils
Signal
Nucleus Recoils
Er
v/c ? 7?10-4
Dense Energy Deposition v/c small Bragg
?0
Differences the Basis of Discrimination
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Simulation (by DRIFT)
40 keV Ar in 1/20 atm Ar
13 keV e- in 1/20 atm Ar
5 cm
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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.
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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
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Mica Result
Snoden-Ifft, Freeman, Price (1994)
58 16O 16 28Si 12 27Al 5 39K
?p (cm2) ?10-37cm2
SD 10-33cm2
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Superheated Droplet Detector (SDD)
Target, C2ClF5 (Liquid) Temp. gt Boiling
Gelatin
10-36 cm2?
10 ?m
Collar et al., (2000)
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Lose the Gelatin get all Target
Really a bubble chamber... CF3Br
Juan Collar and Andrew Sonnenschein (poster
session)
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Distinct Quantities to Measure

• 1) Time Structure of the Pulse
• 2) Pulse Height/Area via
• Ionization (like Ge)
• Scintillation (like NaI)
• Heat/Phonons
• Physical Size of Ionization

NaI
NaI
DAMA does not use this
ER 130-150 KeV (I)
?t?
Gerbier et al., 1998
Width of pulse
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Distinguishing Nuclear Recoil

• Nuclear recoil energy lost mainly to collisions
  with other nuclei
• Nuclear recoils deposit lots of energy in lattice
  excitations phonons... heat
• Nuclear motion poor at causing electronic
  excitation, ionization

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Simultaneous Measurement of Phonons(Heat)
Ionization
Edelweiss

• Temperature-20 mK
• D(Temp)/D(Energy)
• D(Temp)?NTD Ge
• Slow (10s ms)
• Ionization - E applied

E

• Background (e- from ??) strong ionization
  signal equal phonon signal (!)
• Nuclear recoil reduced (by 1/4) ionization
  signal, strong phonon signal

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Separation of Nuclear Recoil from e- Recoil
Nuclear recoils (induced by a neutron source)
Electron recoils (induced by a ? source)
1 (bkgd)
?1/3 (sig)
Shutt et al., 1992
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Edelweiss (depth 4500 mwe)
0.32 kg/ Ge detector
Roman Lead
30.32kg Germanium Detectors
L. Chabert, EPS 03 Aachen
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Edelweiss Data ?s Suppressed by 1000
Bolometer 1
Bolometer 2
Bolometer 3

• 10.86 kg.d (fiducial)
• Good phonon channel
• 300 eV (FWHM)
• resolution during most
• of the runs
• Noisy charge channel
• 30 keV threshold

• 7.51 kg.d exposure
• (fiducial volume)
• Best charg. channel
• 1 keV (FWHM)
• 20 keV threshold

• 3.72 kg.d (fiduc.)
• Smaller exposure due to electronics problems
• 30 keV threshold

L. Chabert, EPS 03 Aachen
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Betas...
Germanium
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Edelweiss and others results
CDMS no background subtraction hep-ex/0306001 28
kg-days (Ge, phonon/ion.)
CDMS with background subtraction
hep-ex/0306001 28 kg-days (Ge, phonon/ion.)
ZEPLIN I (preliminary) 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
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CDMS not as deep neutron background
17 mwe
Active Muon Veto
Pb Shield
Copper
n
n
Fridge
Inner Pb shield
Polyethylene
Detectors
... Experiment moved to Soudan, 2100 mwe depth
R. Schnee
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CDMS Layout, Data
8 cm
4 Germanium Detectors (0.66 kg total) 2 Silicon
Detectors (0.2 kg total) ? Small DM rate, high
neutron rate
R. Schnee
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Technology of ZIPs (Z for z)
Very different from Edelweiss, although the
objective
is the same the phono-cathode
quasiparticle trap
Al Collector
W Transition-Edge Sensor (TES)
quasiparticle diffusion
Cooper Pair
Si or Ge
phonons

• Signal much faster - microseconds
• 3-d imaging (Z)

R. Schnee
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The ZIP Phonocathode...
380m x 60m aluminum fins
1 m tungsten

• 4 segments timing to get x,y on the face
• rise time to get z, into the face

R. Schnee
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ZIP Surface Electron Rejection
Surface electrons still likely to be the
limiting background
R. Schnee
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CDMS Expected Background Levels
In DRU, ev/kg/kev/day
0.0024
CDMS-II Proposal
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Catalog of Recoil Experiments
Rick Gaitskell
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Future Performances
Rick Gaitskell
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Prognostication
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A Proposal 5 billion years ago(indirect DM
detection)
Get 1057 protons in a sphere (ignite to enable
a neutrino program) Wait for WIMPs to collect
(spin-dependent cross section - protons
spin) Detect on a nearby iron ball via the
annihilation of WIMPs (with themselves) to
neutrinos
Review Panels Recommendations/Queries 1)What if
WIMPs dont self annihilate no answer 2) Hey,
youre iron ball is great for collecting WIMPS
via spin-independent scattering, since A of Iron
is big (54)! (thanks) 3) Funding for preliminary
studies...
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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
Sun
lower masses little capture
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Solar/Earth Comparison
(WIMP models for spin/scalar comparison)
Annihilation Rate in Earth is Earth Bottleneck
(for detector on Earth)
Capture Rate in Earth is Earth Bottlneck
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Super-Kamiokandes Results...
Upward going muons
Desai, IDM 02
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Transcribe to the Direct Detection Plot
Model dependent but less so than I thought.
Spin-dependent (Sun)
Scalar (Earth)
Desai, IDM 02
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Future Indirect Detectors (neutrino)
Feng, Matchev, Wilczek 2000
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Cosmic Positrons - Halo WIMP annililation
HEAT terrific balloon experiment saw an excess
Edsjo, IDM 02
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Positron Future ?s too
Feng, Matchev, Wilczek 2000
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Milli-CHAMP Limits
Excluded Regions
Overclose Universe (Thermal)
Charge Fraction
Davidson, Hannestad, Raffelt, hep-ph/0001179
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Stable CHAMPs in Matter
DM, stop in earth
Perl et al., hep-ph/0102033
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Some conclusions

• Rutherford/Chadwick hunted neutron for 12 years
• Hints first seen on continent, interpreted as
  photons
• Neutrino studies started about 90 years ago
• Masses? Majorana? Still not fully nailed
  down...
• Dark Matter
• Prepare for a long ride no physical law
  guarantees that discoveries happen within any
  humans lifetime
• The only guarantee if we fail to look, we will
  fail to find.