The EDELWEISS-II experiment

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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)

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Outline

• Limits of EDELWEISS-I
• EDELWEISS-II setup
• Current situation
• (3 detector types)
• Outlook

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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
• lt 1 ev /kg/week
• Recoil Energy
• 1 100 keV

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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
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EDELWEISS _at_ Laboratoire Souterrain de Modane
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Ge Heat-Ionization Detectors

• Simultaneous measurements
• Ionization _at_ few V/cm with Al electrodes
• Heat _at_ 17 mK with Ge/NTD sensor
• Different Ionization/Heat energy ratio for
  nuclear and electronic recoils (dominate bkg)
• Event by event background rejection

gt discrimination g/n gt 99.9 for Ergt15keV
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Edw-I limiting background
PRD71, 122002 (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

E5.3MeV Q0.3
206Pb
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EDW II set-up

• ? radiopurity
• dedicated HPGe detectors for systematic checks
  of all materials
• ? clean room (class 100 around the cryostat,
  class 10000 for the full shielding)
• ? deradonized air (from NEMO-3)
• ? neutron shielding
• 20 cm Pb shielding
• 50 cm PE and better coverage
• active m veto (gt98 coverage)
• up to 110 detectors
• Ge/NTD Ge/NbSi new ID electrodes
• ? expected sensitivity EDW-I 100
• sc-n ?10-8 pb (phase 100)
• 0.002 evts/kg/day (Ergt10keV)

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Ge-NTD detectors

• 23320g Ge/NTD
• 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)
• All _at_ LSM

first low bg runs in 2006
old bg

• EDW-I g rate 700 evts/kg/day for Egt100keV
• After the most recent improvement
• EDW-II g rate 300 evts/kg/day
• EDW-I ? rate on central electrode
• 2.5 - 5.5 evts/kg/day (400-1000 /m2/day)
• EDW-II ? rate
• 3 evts/kg/day

new bg
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Ge/NbSi detectors
identification of surface events with Ge/NbSi
detector

• 7400g Ge/NbSi detectors
• developed by CSNSM Orsay
• NbSi thin film thermometers for active surface
  evt rejection
• 2 _at_ LSM

data taken with 1 NbSi detector MayJune 2007
1.5kg.d (fiducial)
Rejection works, resolutions needs tuning
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ID detector
a electrodes 2V
after cut b lt 5keV (30 of evts. survive)
all events
b electrodes 1V
Z (cm)
guard g 1V
recoil energy keV
recoil energy keV
ab near- surface event
lab data
Electron trajectories
200g detector, concentric electrodes 2mm gaps,
200µm width trigger thresh. 24keV 241Am source
with 60keV gs
ac bulk event
a,bc event in low-field area
hole trajectories
guard h - 1V
Radius (cm)
d electrodes -1V
c electrodes-2V
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status ID bolometer

• summary
• first detector (200g) with
• interleaved electrodes in LSM
• performance as expected
• New 400g IDs to be installed
• end of March

1.7 kg.d
preliminary!
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EDELWEISS-II next steps

• Goal 2x10-8 pb
• (1200 kg.d no event)
• (1 evt/kg/y)
• acquire physics data with 23 NTD
• build 6 400 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