1. Direct Dark Matter Searches
Véronique SANGLARD
UCBL-CNRS/IN2P3/IPNL
Good afternoon.
This review talk will deal specifically with non-baryonic direct dark matter search from an experimental point of view.

2. Outline Motivations for non-baryonic dark matter search
Principle of the direct detection
Running experiments
Future experiments
Conclusion
After a brief reminder of the main motivations for the search of non-baryonic dark matter, we’ll focus more particularly on the direct detection approach. The main current results and techniques will be presented and shortly discussed when needed, followed by the future plans for larger scales and more sensitive experiments.
We’ll conclude on the likely evolution of this field of research.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

3. Motivations for Dark Matter Search (1)
Rotation curves studies
Dark matter halo around the galaxies
Local density : GeV/cm3
The first evidence for the existence of Dark Matter comes from the observation of galaxies rotation curves. The visible objects (stars) cannot possibly account for the observed speeds distribution, which naturally lead to the idea of a non-visible “dark” matter component.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

4. Motivations for Dark Matter Search (2)
At cosmological scale :
Results of WMAP ->
Ω tot ~ 1.00
Ω baryon < 0.05 (confirmed by experiments like EROS, MACHO)
Ω matter ~ 0.3
Ω Cold Dark Matter ~ 0.22
Need weakly interacting non-baryonic massive particles …
WIMP (σ<10-6 pb)
Lastly, the latest cosmological background measurements, notably by WMAP last year, give the most drastic constraints. Within an apparently flat universe, baryonic matter only amounts to about 5% of the total mass, while the total matter contribution is around 30%, thus leaving at least 85% of non-baryonic matter so far unaccounted for, and therefore supposed to be very weakly interacting.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

5. Natural WIMP candidate
Neutralino definition in the SUSY field
Stable particle if R-parity
conserved (LSP)
Indirect detection :
Detection of WIMPs annihilation
products
Direct detection :
Detection of WIMPs scattering off
nuclei
EDELWEISS
DAMA
SUPER K
AMANDA
This lead to their calling WIMPs, for Weakly Interacting Massive Particles. The most natural WIMP candidate is the Lightest Supersymetric Particle predicted by the Supersymetry theories, namely the neutralino, which is stable if R-parity is conserved. Able to solve this dark matter enigma at the electroweak scale, the neutralino would be a combination of photino, zino and higgsinos.
Two ways of detecting it are envisaged:
The indirect method looks for WIMP annihilation products, such as neutrinos. Annihilations being supposed to occur preferably in high concentration regions such as the center of the sun, a directionality signature is expected. We can cite the SuperK, Antares and Amanda experiments, among others, looking in that direction.
The direct method, which is so far leading in terms of sensitivity and will be developed in this review, is looking directly for WIMP interactions within a target material.
ZEPLIN
ANTARES
CDMS
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

6. Direct Search Principle
Detection of the energy deposit due to elastic scattering on nuclei of detector in laboratory experiment
Optimum sensitivity for MWIMP ~ MRECOIL
Rate < 1 evt/day/kg of detector
Need low background
Deep underground sites
Radio-purity of components
Active/passive shielding
Need large detector mass (kg -> ton)
Recoil energy ~ 20 keV
Need low recoil energy threshold
The principle of the direct detection is very simple. When a WIMP hits a nucleus, this one recoils. This induced nuclear recoil produced measurable effects in the crystal (ionization, scintillation, heat, depending on the target type).
Thus the optimum sensitivity is reached for a nucleus mass similar to the WIMP mass (~50 GeV).
Due to the extremely low expected event rate, maximum background suppression is a vital issue. This is the reason why a number of experiments try to bury themselves as deep as possible to reduce the cosmic muon flux and cosmogenesis within their own detectors. The radio-purity of all the experiments’ components is also usually kept to a minimum. Lastly, the actual detectors can be effectively shielded against natural radioactivity by more or less complex set-ups.
This becomes even more true when one considers the large mass scales, up to one ton, that are envisaged in the next 10 years.
Therefore, the deposited energy by the WIMP in the crystal is very low (~20 keV) so a challenge for the experiments is to reach energy threshold as low as possible.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

7. WIMP signatures Nuclear recoils spectrum shape
Not electron recoils (dominant background)
Neutron scattering also produces recoils …
spectrum shape
Exponential (as most bkg)
Shape for backgrounds : unknown/poorly predicted
Coherent interaction (Spin-independent) ?
Absence of multiple scattering (against neutron)
Uniform rate throughout volume (against surface radioactivity)
Directionality of nuclear recoils
Annual rate modulation
The signatures of a direct WIMP interaction can be multiple:
First comes the nature of the interaction: WIMPs, like neutrons, scatter off nuclei, while gammas and electrons scatter off the electronic cloud.
Second, to each given WIMP mass is also associated an expected energy spectrum with an exponential shape. One problem is the non-knowledge of the background spectrum shape.
The spin-dependent (scalar) interaction dominate almost always because of coherent interactions (cross section prop. A²) -> study of large A target.
Because of the weakly interaction of the WIMP with matter, it can’t make multiple scattering contrary to neutron.
And the interaction rate is independent of the position in the detector (contrary to surface interaction produced by radioactivity).
With sufficient statistics the directionality of nuclear recoils can be looked, and because of the motion of the earth around sun, the WIMP wind varies during the year.
Lastly, the consistency between results acquired with different techniques and target materials, with different expected energy spectra, would certainly strengthen any eventual WIMP discovery.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

8. Direct detection techniques
WIMP
Heat
Ionization
Light Ge
Liquid Xe
NaI, Xe
Ge, Si
CaWO4, BGO
Al2O3, LiF
Elastic nuclear scattering
1% energy fastest no surface effects
10% energy
100% energy slowest cryogenics
Target
For any material, however, the principles behind direct detection are always the same. It all comes down to measuring the energy deposited by a WIMP interaction – expected to be in the keV to tens of keV range. There are basically three ways of measuring this energy, which can eventually be combined. Each leads to a choice of target material.
The fastest but less efficient way – in terms of collected energy – is to look for a light signal produced by a scintillation process. This is the way used in Sodium Iodide or Xenon scintillators.
One can also look for a ionization signal: free charge carriers produced by the nuclear recoil can be collected using a drifting electrical field. Depending on the material used and operating conditions, the efficiency of this technique can be significantly higher than that of scintillation.
Lastly, a slower heat signal can be detected, assuming that all energy deposited will eventually turn into heat. This technique usually ensures a higher energy collection efficiency, to the cost of a slower signal and tougher operating conditions – namely ultra-low cryogenics.
With the measurement of two quantities, it is possible to discriminate a main part of the background induced by gamma.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

9. Current direct detection experiments
Discrimination
Name
Location
Technique
Material
Status
CUORICINO
Gran Sasso
Heat
41 kg TeO2
running
GENIUS-TF
Ionization
10 to 40 kg Ge in N2
running ???
HDMS
0.2 kg Ge diodes
stopped
IGEX
Canfranc
2 kg Ge Diodes
DAMA
Light
100 kg NaI
LIBRA
250 kg NaI
NaIAD
Boulby mine
46 kg NaI
ZEPLIN-I
4 kg Liquid Xe
XENON
Surface to GS
Light+ Ionization
3 to 10 kg Liquid Xe
ZEPLIN II
6 kg Liquid Xe
CDMS-I
Stanford
Heat + Ionization
1 Kg Ge Kg Si
CDMS-II
Soudan mine
2 to 7 kg Ge to 1.4 Kg Si
CRESST-I
Heat + Light
0.262 kg Al2O3
CRESST-II
0.6 to 9.9 kg CaWO4
EDELWEISS-I
Modane
1 kg Ge
EDELWEISS-II
10 to 30 kg Ge
In istallation
PICASSO
SNO
Bubble chamber
20 g Freon
ROSEBUD
50 g Al2O g Ge + 54 g CaWO4
None
Statistical
Taking into account all those parameters has lead to a number of experiments, set in various underground sites all over the world. In this table are reported the most notable or representative of them, which have given results or are still running. For ease of view they are sorted by way of nuclear versus electronic recoil discrimination capabilities.
The first generation experiments used only one way of measure, be it Heat, Ionization, or Light. However, this lead to very little to no background discrimination capabilities. HDMS or IGEX Ge diodes, or CUORICINO TeO2 crystals, are examples of detectors which can’t discriminate nuclear from electronic recoils events. DAMA Sodium Iodide crystals, or ZEPLIN Liquid Xenon setups only allow a limited and statistical discrimination.
Next generation detectors aiming to obtain an energy spectrum almost all include two channels of measure. This is the case with the Heat and Ionization or Heat and Light bolometers, and the new LXe detectors with Light and ionization measurement.
We’ll now go through the most notable and representative experiments…
Be careful with the comparison of experiments, we must use the same prescriptions as Lewin and Smith (example for the halo parameters, the form factor, …)
Event-by-event
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

10. NaI scintillation : DAMA
PMT
Based in Gran Sasso lab (3500 mwe)
100 kg of NaI(Tl)
Exposure : kg.d
Coincidence between 2 PMTs
Pulse shape rejection inefficient at 2 keVee
Used annual modulation
Claim annual modulation at 6.3σ over 7 annual cycles
Mχ ~ 52 GeV/c²
σn ~ pb
Not compatible with CDMS, EDELWEISS experiments
Future = LIBRA (250 kg of NaI)
Starting with the Sodium Iodide scintillator experiment DAMA.
The data taking was completed in July 2002, with a total exposure of over 107,731 kg.d accumulated over 7 years.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

11. NaI scintillation : DAMA
Based in Gran Sasso lab (3500 mwe)
100 kg of NaI(Tl)
Exposure : kg.d
Coincidence between 2 PMTs
Pulse shape rejection inefficient at 2 keVee
Used annual modulation
Claim annual modulation at 6.3σ over 7 annual cycles
Mχ ~ 52 GeV/c²
σn ~ pb
Not compatible with CDMS, EDELWEISS experiments
Future = LIBRA (250 kg of NaI)
The published results show a modulation confirmed at 6.3 sigma significance using the 2 to 6 keV energy range data, which has lead the DAMA collaboration to claim a model-independent evidence for the presence of WIMPs in the galactic halo. Under standard halo parameters, this translates to a WIMP candidate of mass around 52 GeV and cross-section to the minus 6 picobarn. This analysis is model-independent. They see no modulation above 6 keVee
As we’ll see in the following, this result has been controversial since quite some time now. To this day, confronting this result to their own data remains for a lot of experiments, if not a goal, at least an important milestone.
Single-hits events residual rates
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

12. Ge ionization : GENIUS-TF
Based in Gran Sasso lab (3500 mwe)
Running experiment
4x2.5 kg (up to 14) naked HPGe in N2
Problems surface contamination by Radon
Goal for background : count/(kg.keV.y) < 50 keV
But serious problems for GENIUS (1T of Ge in N2)
Also based in Gran Sasso, the Genius- Test Facility experiment is using 10 kg of enriched High Purity Germanium crystals operated at liquid nitrogen temperature, and placed behind heavy shielding, to try and see the DAMA modulation. The final setup could receive 35 kg of Ge.
But after some data takings, a surface contamination of the Ge detectors have been observed due to Radon. It is more difficult to remove it than the Genuis member have think.
They now try to improve the elimination of the radon to reach a goal of 1 evt per kg per kev per year below 50 keV. But this radon problem induced very serious questions about the bigger experiment GENIUS proposed with 1T of Ge.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

13. Liquid Xe Scintillation : ZEPLIN-I
Based in Boulby mine (2800 mwe)
3.2 kg (fid.) -> 230 kg.d
Single phase
3 PMTs coincidence
Pulse Shape Amplitude (time constant discrimination)
Difficulties with neutron calibration at low energy (in deep site)
Resolution 100% at 40 keV (7 keVee)
Experiment now completed but no published results yet
Future : ZEPLIN II (30 kg) Ionization+scintillation
Xe*
+Xe
Xe2*
Triplet
27ns
Singlet
3ns
2Xe
175nm
Xe** + Xe
Xe2+
+e-
(recombination)
Xe+
Ionization
Excitation
Electron/nuclear recoil
We’re now looking at a whole other concept, which is that of Xenon scintillators.
ZEPLIN is a 3.2 kg single Phase Xenon experiment based on the Xenon excitation principle.
The light pulse rise-time constant is analyzed, and showed to be slightly different for electronic and nuclear recoils.
With a 230 kg.d data set accumulated over 75 days live time, ZEPLIN displays some promising yet ambiguous results.
However, neutron calibrations – which are essential for understanding a WIMP signal - seem to be at the very least challenging at low energies.
All of this is still preliminary, as ZEPLIN has not yet made any definite announcement.
A recoil in Lxe induce both ionization and excitation of Xe atoms. The excitation produce photon emission with 175nm by a singlet or a triplet. The ratio singlet over triplet is ten times bigger for a nuclear recoil than electronic recoil.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

14. Liquid Xe Scintillation+Ionization : XENON
Prototype 3kg (active mass) dual phase detector with TPCs
7 PMTs in the cold gas above the liquid
Measurements of
Primary scintillation light (S1)
Secondary scintillation light from ionization electrons (S2)
CsI photoelectron signal (S3)
Discrimination variable S1/S2
Current work
Calibrations (γ, α, neutrons)
Future : XENON10,100,1T in Gran Sasso lab S1 S3
Representing Xenon experiments, the XENON project is a dual phase Xenon experiment, which will allow it to collect both a light and an ionization signal. It uses Time Projection Chambers as showed on the schematic on the right:
A WIMP interaction creates a primary scintillation light, collected by the PMT array, and charge carriers which are drifted throughout the liquid phase, turned into proportional light by electroluminescence and collected by the same PMTs. A photocathode deposited at the bottom of the chamber provides a “second primary” signal, and allows Z positioning.
A prototype with 3kg has already been successfully operated, and a larger 10 kg prototype is underway and will place underground in 2005. S2
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

15. Liquid Xe Scintillation+Ionization : XENON
Electronic recoils
Nuclear recoils
First plot showing neutron
calibration with Liquid Xe
Prototype 3kg (active mass) dual phase detector with TPCs
7 PMTs in the cold gas above the liquid
Measurements of
Primary scintillation light (S1)
Secondary scintillation light from ionization electrons (S2)
CsI photoelectron signal (S3)
Discrimination variable S1/S2
Current work
Calibrations (γ, α, neutrons)
Future : XENON10,100,1T in Gran Sasso lab
Simulation of
detector
response
for neutron
calibration
With the prototype some calibrations have been made. This plot show the discrimination variable S2 over S1 versus S1. We can distinguish the 2 populations due to electronic or nuclear recoils. This is the first like plot for a liquid xenon experiment.
The final goal of the XENON experiment is the 1 ton scale, with a 16 keV recoil threshold and impressive background rejection capabilities. It aims at reaching 10 to the minus 10 pb within 3 years. Some experiment will be test before with 10, 100 and finally 1000 kg of Lxe.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

16. Phonon and scintillation/ionization bolometers
Simultaneous measurement of phonon and scintillation/ionization
Different (light or charge)/heat ratio for nuclear and electron recoils (WIMP and neutron have lower light/charge than γs, βs )
Discrimination event-by-event of electron recoils (main background)
Now we’re switching to discriminative experiments.
The simultaneous measurement of heat and scintillation or ionization signal provide a good discrimination between nuclear and electron recoils.
As an example, here is the data recorded in a calibration run with a 252 californium source for the EDELWEISS experiment. In addition to gamma rays, we can see nuclear recoils induced by neutron scattering that permit to simulate WIMP recoils.
This graph represent the ionization over recoil energy versus the recoil energy, the units are keV. On this 2 populations can be distinguished. One centered at one by convention represents electron recoils induced by gammas. The second centered at about 0.3 corresponds nuclear recoils.
Taking into account the experimental resolutions, the full lines represent 90% of these populations. This type of figure show the possibility to discriminate gammas, here more than 99.9% above a recoil energy of 15 keV.
The green full line represent the ionization threshold. The magenta lines represent the inelastic scattering of neutron on 73Ge(n,n’,γ).
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

17. Heat-scintillation : CRESST-II
Based in Gran Sasso lab (3500 mwe)
2x300g CaWO4 crystal +W-SPT
Net exposure: ~ 20.5 kg.d
Rejection at 15 keV: 99.7%
No neutron shield installed
WIMP interact mainly with W
Energy range: keV
separate cryogenic
light detector
W SPT
(W-Superconducting
Transition Thermometers)
CRESST is already launching its second phase, now operating two CaWO4 crystals. Their recent published results are based on an exposure of 20.5 kg day.
In is important to note that this results have been recorded without neutron shield around the experiment. Because of the cinematic effects, a WIMP will interact mainly with the W nucleus of the target. The interesting recoil energy range is 12 to 40 keV.
absorber :
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

18. Heat-scintillation: CRESST-II
90% of nuclear recoils
with quenching factor
Q=7.4 below this line
90% of nuclear recoils
with Q=40 (W) below
this line
0 events
(between 12 and 40 keV)
Only this detector used to
derive exclusion limits
This is the results for the two detectors. These plots represent the light yield versus the phonon energy in keV. 90% of nuclear recoils with a quenching factor of 40 (W) are below the full line. For the second detector 0 events appear below the full line and between 12 and 40 keV. With the results of the best detector (daisy) Cresst has derived an exclusion limit considering only nuclear recoils on the W.
Only one problem keeps about the quenching factor values. The Q for the W has only been measured at room temperature.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

19. Heat-ionization: CDMS-II
ZIP 1 (Ge)
ZIP 2 (Ge)
ZIP 3 (Ge)
ZIP 4 (Si)
ZIP 5 (Ge)
ZIP 6 (Si)
SQUID cards
FET cards
4 K
0.6 K
0.06 K
0.02 K
Based in Soudan Underground lab (2090 mwe)
4x250g Ge x100g Si
Net exposure: kg.d
Detector = ZIP (sensitive to athermal phonon)
Active muon veto + shielding (PE + Pb)
Set in the Soudan Underground Lab, the American Cold Dark Matter Search used heat and ionization cryogenic Germanium and Silicium bolometers, which are sensitive to out-of-equilibrium phonons and thus allow pulse-shape analysis as well as limited bi-dimensional impact position determination.
In this second phase, they used the same detector as in the previous work
The data taking is now complete, with a 19.4 kg.d data set.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

20. Heat-ionization: CDMS-II
Rejection of background surface events with timing cuts
To reject surface electron recoils, they made a timing cut defining with neutron, beta and gamma calibrations.
These plots show the data recorded with three of the four detector. One required a higher energy threshold (20 keV instead of 10), and it is not considered here. After all cuts no events appear in the nuclear recoil band above 10 keV. One event passed all the cut in Z1 at 50 keV. At low energy, the limits are very similar taking into account 3 detectors and 0 events, or 4 detectors and 1 event.
With these results they obtained the best limits on the wimp nucleon cross section
0 events
(between keV)
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

21. Heat-ionization: EDELWEISS-I
Based in Modane Underground laboratory (4800 mwe)
Low radioactivity dilution cryostat at 17 mK
Shielding : PE+Pb+Cu
3x320g Ge
Amorphous layer (Ge/Si)
NTD Ge thermometric sensor
Al electrode (one segmented)
Fiducial volume: 57%
Rejection-γ 99.9% at 15 keV
On a pretty similar principle, we find the Edelweiss experiment. Set in the Modane underground Lab, with an incident muon flux reduction by more than 6 orders of magnitude, it consists of 1 kg total mass of Ge in 3 detectors, operated at 17 mK. The experiment is further protected by several layers of shielding, for an optimized radioactive background.
The detectors themselves are 320g Germanium crystals, equipped with an amorphous Germanium or Silicon sub-layer to limit anomalous surface events, electrodes for charge collection split in two for a better definition of the fiducial volume, and a NTD thermal sensor glued directly onto the crystal.
3x320g heat-and-ionization
Ge cryogenic detectors
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

22. Heat-ionization: EDELWEISS-I
New data taking with trigger on phonon signal
Improved efficiency at low energy (50 % at 11 keV)
Fiducial exposure: 22 kg.d
Stable behavior over 4 months
18 nuclear recoil candidates > 15 keV
1 n-n coincidence
Possible backgrounds
Residual neutron flux
Miscollected charge events
Not enough statistics to conclude
The results of a first data taking were published in summer 2002 with a total fiducial exposure of 13.6 kg.d, keV resolutions and zero events in the nuclear recoils band.
19 additional kg.d were added in a first run in 2003, but with electronic problems on one detector and 2 events in the nuclear recoil band above the recoil energy threshold.
Finally a new run have been made using a new “phonon” trigger acquisition system, and improved resolutions. One important point is the improvement of the efficiency at low energy. 22 kg.d have been added with 18 events in the nuclear recoil band above 15 keV.
One neutron-neutron coincidence have been observed, maybe a neutron background ? But the number of events between the nuclear and electron recoils bands is small, but some leakage in the nuclear band is possible. The statistics are not large enough to conclude.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

23. Heat-ionization: EDELWEISS-I
Final results: 62 kg.d (fid. exp.)
50% trigger efficiency at 15 keV
40 nuclear recoil candidates > 15 keV (only 6 > 30 keV)
Unknown background
Used method developed by S. Yellin to derive exclusion limits (as CDMS)
No background subtraction
New limits consistent with previous published results
V.Sanglard et al. astro-ph/ (to PRD)
Experiment stopped in March 2004
Finally the results of the entire edelweiss one experiment represent a fiducial exposure of 62 kg.d with a trigger efficiency of 50 % at 15 keV.
40 events have been recorded in the nuclear recoil band but only 3 are above 30 keV. As the possible background is unknown a subtraction is not possible. So the optimum interval method have been used as CDMS and CRESST.
As we will see in the next slide, the new limits are consistent with the previous limits.
These results are published in the astro-ph 0503xxx submitted to PRD.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

24. 90% C.L. exclusion limits on WIMP-nucleon scattering cross-section (spin-independent)
So to sum this all up, here are the current exclusion limits as they appear in the most recent published papers. Recent papers have shown that this exclusion resists to even drastic variations of halo parameters.
But the search still continues...
Only published
results are reported
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

25. Next step for running experiments
CDMS-II
7 towers (=4x250g Ge + 2x100g Si)
2 running now
CRESST-II
33x300g CaWO4
Wiring to mK level
New readout system
Neutron shielding + μ veto
EDELWEISS-II
Next slide
Whichever technology is used, one of the strong key points always resides in the understanding of the physics of the detectors. Most next generation experiments put an emphasis in their design to ensure that they know more and more precisely what exactly they’re looking at.
I will now go over the operating principles of a few of those.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

26. EDELWEISS-II
Low radioactivity cryostat with larger experimental volume (50 liters)
Improved neutron shielding
Addition of μ veto
1st phase: 28 detectors (21x320g Ge+7x400g NbSi)
Up to 120 detectors
Expected sensitivity: evt/kg/day
Installation in progress in LSM
Representing cryogenics experiments, the second phase of the EDELWEISS experiment will go from 6 kg to eventually 35 kg of Germanium bolometers.
It should start operating up to 28 detectors early 2005.
It comes with an additional muon veto, and a new test detector technology which should allow sensitivity to out-of-equilibrium phonons, and a better rejection of anomalous surface events which are a suspected source of background limitations.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

27. Conclusion Today: 10-6 pb era Next step: 10-8 pb
Starting to test most optimistic SUSY models
Next step: 10-8 pb
Increased detector mass
Further reduce background rejection
Lower energy threshold
Improve event-by-event discrimination
Goal: pb within 10 years
Probe most of the allowed SUSY parameter space
1 ton scale (SuperCDMS, EURECA)
Combined several targets
All this leads to the following summary exclusion diagram prediction.
In blue, yellow and green are allowed SUSY parameter spaces. The current best limit, which you can see is already excluding a first part of the supersymetric models.
The next phase of experiments, Edelweiss-II, CDMS-II, etc... Are aiming for a 10 to the minus 8 pb sensitivity, which should allow them to test a much more significant part of the parameters space. This will come to the price of an increased detector mass, further background rejection, lower energy threshold and improved discrimination.
The 1 ton scale experiments are aiming two orders of magnitude lower, for 10 to the minus 10 pb, which would probe most of the interesting parameters space. Projections at this point remain hazardous, but it is already clear that both experimental issues and data analysis will prove very challenging. Combining results from different target materials, cross-checking with different signatures such as the directionality of interactions, may be the only way to ever ascertain the existence of WIMPs.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

28. Conclusion Today: 10-6 pb era Next step: 10-8 pb
Starting to test most optimistic SUSY models
Next step: 10-8 pb
Increased detector mass
Further reduce background rejection
Lower energy threshold
Improve event-by-event discrimination
Goal: pb within 10 years
Probe most of the allowed SUSY parameter space
1 ton scale (SuperCDMS, EURECA)
Combined several targets
With these projection for ideal detectors (1T mass, 20 keV threshold) we can see that the limit reach could be below 10 to minus 10. And an important think is that detector made in Ge or in Xe show a limit very similar.
Then again, we might very well never find anything. But this alone would be an interesting result.
Thank you for your attention.
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05

29. 1 ton : a simple experiment ?
V. SANGLARD Rencontres de Moriond 2005 « Very High Energy Phenomena in the Universe » La Thuile /03/05