1. The EDELWEISS-II experiment
Silvia SCORZA
Université Claude Bernard- Institut de Physique nucléaire de Lyon
CEA-Saclay DAPNIA/DRECAM (FRANCE), CNRS/CRTBT Grenoble (FRANCE),
CNRS/IN2P3/CSNSM Orsay (FRANCE), CNRS/IN2P3/IPN Lyon (FRANCE),
CNRS/INSU/IAP Paris (FRANCE), CNRS-CEA/Laboratoire Souterrain de Modane (FRANCE), JINR Dubnia (RUSSIA), FZK/Universtat Karlsruhe (GERMANY)

2. Outline Limits of EDELWEISS-I EDELWEISS-II setup Current situation
(3 detector types)
Outlook

3. Direct Search Principle
Detection of the energy deposited due to elastic
scattering off target nuclei
Low energy threshold
Large detector mass
Low background
Radio – purity
Active/passive shielding
Deep underground sites
Event Rate :
< 1 ev /kg/week
Recoil Energy :
1 – 100 keV

4. The EDELWEISS collaboration
 CEA Saclay (DAPNIA & DRECAM) Detectors, background, analysis, electronics, acquisition
E. Armengaud, O. Bessida, M. Chapellier, G. Chardin, G. Gerbier, H. Deschamps,
M. Fesquet, M. Gros, S. Hassani, S. Hervé, M. Karolak, X-F. Navick, P.Pari, B. Paul
Post-doc: R. Lemrani, F. Schwamm Thesis : E. Grémion, A. Chantelauze (cotutelle FZK)
 CSNSM Orsay Detectors, cabling, cryogenics, analysis
L. Berge, A. Broniatowski, D. Carré, S. Collin, L. Dumoulin, A. Juillard, F. Lalu, S. Marnieros
Post-doc: Emilano Olivieri Thesis : O. Crauste, X. Defay, Y. Dolgorouki, C. Nones
 IPN Lyon Electronics, background, analysis, detectors
F. Charlieux, M. De Jésus, P. Di Stefano, J. Gascon, M. Stern, V. Sanglard, L. Vagneron
Thesis : S. Scorza, M.A.Verdier
 IAP Paris Low radioactivity, analysis
C. Goldbach, G. Nollez
 CRTBT Grenoble Cryogenics, electronics
A. Benoit, M. Caussignac, H. Rodenas
 FZK/ Uni Karlsruhe (TH) Vetos, background
N. Bechtold, J. Blümer, K. Eitel, V. Kozlov Thesis : A. Chantelauze (cotutelle CEA), H. Kluck
 JINR Dubna Background
E. Yakushev, A. Smolnikov Thesis : A. Lubashevski, L. Perevozchikov
  50 persons (30 FET), 11 PhD theses, 3 post-docs

5. EDELWEISS @ Laboratoire Souterrain de Modane

6. Ge Heat-Ionization Detectors
Simultaneous measurements:
few V/cm with Al electrodes
17 mK with Ge/NTD sensor
Different Ionization/Heat energy ratio for nuclear and electronic recoils (dominate bkg)
Event by event background rejection
=> discrimination g/n > 99.9% for Er>15keV

7. Edw-I limiting background
PRD71, (2005)
Best Sensitivity up to 2003, but…
 Background in the physics data taking
 Leakage from the g to the recoil band
Neutrons:
- 1 n-n coincidence observed
- Neutron shield not thick enough
Surface electron recoils:
- Bad charge collection (trapping and recombination)
- Rate compatible with 210Pb contamination:
rate a  “e-”  5/kg.day
E=5.3MeV Q=0.3
210Pb
210Po a b
206Pb

8. EDW – II set-up  radiopurity
dedicated HPGe detectors for systematic checks of all materials
 clean room (class 100 around the cryostat, class for the full shielding)
 deradonized air (from NEMO-3)
 neutron shielding
20 cm Pb shielding
50 cm PE and better coverage
active m veto (>98% coverage)
up to 110 detectors
Ge/NTD + Ge/NbSi + new ID electrodes
 expected sensitivity: EDW-I × 100
sc-n 10-8 pb (phase 100)
= evts/kg/day (Er>10keV)

9. Ge-NTD detectors 23*320g Ge/NTD : first low bg runs in 2006: old bg
Developed by CEA Saclay and
Canberra-Eurisys
Amorphous Ge and Si sublayer:
better charge collection for surface evts
Optimized NTD size and homogeneous
working T (16-18 mK) :
goal keV resolution
New holder and connectors
(Teflon and copper only)
LSM
first low bg runs in 2006:
old bg
EDW-I g rate: ~ 700 evts/kg/day for E>100keV
After the most recent improvement
EDW-II g rate: ~ 300 evts/kg/day
EDW-I  rate on central electrode :
evts/kg/day ( /m2/day)
EDW-II  rate
~ 3 evts/kg/day
new bg

10. Ge/NbSi detectors 7*400g Ge/NbSi detectors :
identification of surface events with Ge/NbSi detector
7*400g Ge/NbSi detectors :
developed by CSNSM Orsay
NbSi thin film thermometers for active surface evt rejection
LSM
data taken with 1 NbSi detector
May&June 2007: 1.5kg.d (fiducial)
200
150
100 50 80 60 40 20
x10 -3
Transient T
hermal
Heat signal of thermometer
NbSiA :
Surface event
Bulk event
Thermometer
NbSi B A
Time (ms)
Rejection works, resolutions needs tuning

11. ID detector lab data all events ‘a&b’ near- surface event ‘a&c’
‘a’ electrodes:
+2V
after cut “b” < 5keV
(30% of evts. survive)
all events
‘b’ electrodes: +1V
Z (cm)
guard
‘g’: + 1V
recoil energy [keV]
recoil energy [keV]
‘a&b’ near-
surface event
lab data
Electron
trajectories
200g detector,
concentric electrodes
2mm gaps,
200µm width
trigger thresh. 24keV
241Am source with 60keV g´s
‘a&c’
bulk event
‘a,b&c’ event in
low-field area
hole
trajectories
guard ‘h’: - 1V
‘d’ electrodes: -1V
Radius (cm)
‘c’ electrodes:-2V

12. status ID bolometer preliminary! summary: first detector (200g) with
interleaved electrodes in LSM
performance as expected
New 400g ID´s to be installed
end of March
~1.7 kg.d
preliminary!

13. EDELWEISS-II next steps
Goal 2x10-8 pb
(1200 kg.d no event)
(~1 evt/kg/y)
acquire physics data with 23 NTD
build g NbSi
Goal 2x10-10 pb
(~10 evt/t/y)
build 16 NbSi
(same/tuned if needed)
build 24 NTD with reduced contamination and/or with ID electrodes