1. Experimental dark matter searches

2. Weakly Interacting Massive Particles
A WIMP c is like a massive neutrino: produced when T >> mc via annihilation
through Z (+ other channels); annihilation/pair creation maintain thermal equilibrium
If interaction rates high enough, the density drops as exp(- mc/T) as T
drops below mc: annihilation continues, production becomes suppressed
But, weakly interacting
 may freeze out
before total annihilation if
> Gann~ nc ann v
i.e., if annihilation too slow to keep up
with Hubble expansion
Leaves a relic abundance:
c h2 10-27 cm3 s-1 ann v
freeze out 
if mc and ann determined by electroweak physics, then c~ 1

3. 0 0 Detecting WIMPs  v/c  10-3 m nm Direct detection:
WIMPs elastically scatter off nuclei nuclear recoils
Measure recoil energy spectrum in target
Indirect detection:
WIMPs annihilate
in halo: e+, p, g
in Sun, Earth core: high energy n’s 
v/c  10-3 m nm 0

4. Direct detection c c ~ H,h,Z q q WIMP flux s-wave scattering Ge Si
WIMPs elastically scatter off nuclei in targets, producing nuclear
recoils, with nc related to ann
(same diagrams - via Z, h, H, and squarks)
Energy spectrum of recoils is exponential with E ~ 50 keV,
dependent on WIMP and target nucleus masses: Boltzmann
distribution (isothermal halo) + s-wave scattering (NR) c
H,h,Z q c q ~
WIMP flux
Amplitude of recoil energy spectrum, i.e. event rate,
normalized by nc, local WIMP number density, and
nucleus-dependent A2F2 (Q)
s-wave scattering
I/Xe Ge Si
Elastic Scattering Form Factors
At low Q, scattering is coherent
and ~A2. Coherence lost as Q
increases; parameterized by form factor.

5. WIMP nucleus cross section
In MSSM/CMSSM (neutralino):
in general: s: 10-5 between and pb
sensitivity of current experiments: ~ 10-6 pb
testing some models, will test more models
in future as sensitivity improves
Accelerator constraints shrink SUSY bounds:
mainly constrained upper bound
g-2 can provide constraint on lower
bound if tentative disagreement due to SUSY
1 event kg-1 d-1
current experiments
1 event 100 kg-1 yr-1
detectors:
low threshold
low background
large masses
good event discrimination

6. WIMP signatures v0 Annual modulation: galactic center Sun 230 km/s
WIMP Isothermal Halo (assume no co-rotation) v0~ 230 km/s
WIMP wind
June v0
galactic center
Sun 230 km/s
Dec.
log dN/dErecoil
Erecoil
June
Dec
~3% effect
Earth 30 km/s (15 km/s in galactic plane)

7. Annual Modulation WIMP Signal Background ±2%
Not distinguish between WIMP signal and background directly
From the amplitude of the modulation, we can calculate the
underlying WIMP interaction rate
WIMP Signal
±2%
Background
Dec
June
Dec
June
Dec
June
Dec
June

8. WIMP signatures Diurnal modulation: vo a v0: solar motion
Nuclear recoil
The mean recoil direction rotates over
one sidereal day
The distribution of the angle a between the
solar motion and recoil directions:
peaks at a=180o

9. WIMP signatures WIMPS 40 GeV Background neutrons Material dependence:
WIMPs: Ge has ~6x higher interaction rate per kg than Si
neutrons: Si has ~2x higher interaction rate per kg than Ge
WIMPS 40 GeV
Background neutrons

10. Direct detection techniques
CRESST
ROSEBUD
CUORICINO ER
Phonons
Ionization
Scintillation
CDMS
EDELWEISS
CRESST II
ROSEBUD
HDMS
GENIUS
IGEX
MAJORANA
DRIFT (TPC)
DAMA
ZEPLIN I
UKDM NaI
LIBRA
XENON
ZEPLIN II,III,IV
Large spread of technologies:
varies the systematic errors, important if positive signal!
All techniques have equally aggressive projections for future performance
But different methods for improving sensitivity

11. Where do we stand? ~ 1 event/kg/day DAMA 3s CDMS
Most advanced experiments
start to test the predicted
SUSY parameter space
One evidence for a positive
WIMP signal
Not confirmed by other
experiments
CDMS
EDELWEISS
ZEPLIN I
Predictions: Ellis, Baltz & Gondolo, Mandic & all

12. The DAMA/LIBRA experiment
At LNGS (3800 mwe)
9 x 9.7 kg low activity NaI crystals,
each viewed by 2 PMs
2 methods of backgrd discr:
PS; annual modulation
-> positive signal (4 s)
What next?
update to LIBRA (250 kg)
improved backround (~few)
improved light yield
Installation completed;
analyze additional 3 yr
of DAMA data (finished Jan 02)
Day 1 = Jan 1, 1995

13. The CDMS II experiment gamma source neutron source neutrons gammas
At SUF (16 mwe) /Soudan (2030 mwe)
uses advanced athermal phonon (TES)
measuring charge and phonons
discrimination
position resolution
surface event rejection
gamma source
neutron source
neutrons
gammas
electrons

14. The CDMS II experiment 1 tower of 4 Ge and 2 Si ZIPs
operated at SUF ; > 120 livedays
> % rejection of bulk electron recoils: keV
> 99 % rejection of surface events: keV
n background x 2.3 lower due to inner poly (as expctd);
20 Ge recoil single scatters, 2 Si single scatters,
2 triple scatter, 1 nnn double scatter; consistent
with all single scatters caused by neutrons
first results submitted to PRL, hep-ex/
SQUID cards
FET cards Si Ge Ge Si
Muon anticoincident background

15. CDMS and DAMA
assumptions of standard halo, standard WIMP interactions
CDMS results incompatible with DAMA model-independent annual-modulation data (left) at > 99.8% CL even if all low-energy events were WIMPs
predicted WIMP modulation
predicted WIMP spectrum alone
Best simultaneous fit to CDMS and DAMA predicts too little annual modulation in DAMA, too many events in CDMS (even for no neutron background)
CDMS data
neutron spectrum fit

16. The CDMS II experiment first 2 towers at the Soudan mine (2030mwe)
m-flux reduced by 104, n-flux by ~ 300
first dark April 03!
goal: 5 towers, 4 kg Ge, 1.5 kg Si
0.1 events/kg/keV/yr
No SUSY gm-2
Baltz&Gondolo,
PRL 86 (2001) 5004
SUSY gm-2
CMSSM
Ellis et al. (2001)
PRD 63,
EDELWEISS
CDMS 03
CDMS Soudan
entrance to the mine

17. The EDELWEISS experiment
In Frejus UL (4800 mwe); 320 g Ge crystals
measure thermal phonons + charge
EDELWEISS I: 1 kg stage
fall 2000, first semester 2002,
October March 2003
total exposure:
13.8 kg  Erec > 20 keV,
30.5 kg  Erec > 30 keV
Incompatibility with DAMA candidate
(99.8% C.L.) confirmed with three different
detectors and extended exposure
G. Chardin 2003

18. The EDELWEISS experiment
New run started: improved energy threshold
≈100% detection efficiency at 10 keV ER
September 2003:
end EDELWEISS-I run
install EDELWEISS-II
21  320 g Ge-NTD detectors
7 thin film (NbSi) 200 g Ge detectors
Achieve factor 100 improvement
in sensitivity
100 l dilution
cryostat for up to
120 detectors (36 kg Ge)

19. The ZEPLIN I experiment
Operating at the Boulby mine (~3000 mwe)
Single phase, scintillation in LiXe, PSD
3.7 kg liquid Xe (3.1 kg fid vol)
1 ton liquid scintillator veto
75 d livetime, 230 kg d of data
Neutron source
Gamma source
10-20keV
Background:
40 100keV implies
85Kr < atoms/atom
(standard Xe used)
Fiducial
Volume
cut

20. The ZEPLIN experiment ER Xe+ Xe2+ Xe**+ Xe Xe2* Xe* 2Xe
ZEPLIN II at RAL, UK
ZEPLIN I ER
Ionisation
Excitation
Xe+
+Xe
Xe2+
+e-
Xe**+ Xe
Xe2*
Xe*
2Xe
175nm
Triplet
27ns
Singlet
3ns
Future ZEPLIN I:
more data, low Kr Xenon
ZEPLIN II/III:
Ionization + scintillation, 2 phase Xe;
30 kg, 6kg high field
II: tested at RAL, UK, PMs being produced
to be installed at Boulby in 2003

21. The DRIFT experiment In the Boulby mine (3000 mwe)
Cathode
Electric Field
Scattered WIMP
Recoil Atom
Drift direction
MWPC Readout Plane
CS2
Recoil
Electron
In the Boulby mine (3000 mwe)
Resolve ionization tracks in a gas
TPC filled with low-pressure EN gas (CS2)
Endcap sense-planes: determination of range,
orientation & energy (via ionization)
e--capture by CS2 suppresses diffusion
during charge-drift
operates at ~40 torr , 140 g target mass
discrimination through dE/dx measrmnt
Future: DRIFT-II
scaled-up DRIFT-I with full 3D readout
& x50 sensitivity
R&D: higher-resolution readout,
higher-pressure operation
cathode-readout of positive ions
allowing event localization away
from wire planes
Gamma Region
Overlap Region
Neutron Region
gamma region
neutron region
overlap

22. The ‘far’ future 1 event/100 kg yr: future projects!
1 event/kg d: EDELWEISS, CDMS, ZEPLIN
1 event/kg yr: CDMSII, CRESSTII, EDELWEISSII,
ZEPLINII
1 event/100 kg yr: future projects!
1 ton is needed in order to detect
10 events per year at s = cm2
Predictions: Bottino, Ellis, Gondolo

23. The ‘far’ future Project Discrimin Type Mass Location CryoArray Yes
Ge/Si
phonon/ioniz
1 ton
NUSEL
CRESST/
EDELWEISS
Ge, CaWO4?
phonon/ion/scint
100 kg - 1t
Gran Sasso?
Zeplin IV
LiXe ioniz/scint
2 phase
Boulby
XENON
(10 x 100 kg)
DRIFT3
Yes + direction
TPC (CS2)
negative ion
100 kg
GENIUS No
Ge ionization in LiN
100 kg -1 ton
Gran Sasso
Majorana
Ge ionization
500 kg