The EDELWEISSII 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 Dubna
  (RUSSIA), FZK/Universtat Karlsruhe (GERMANY)

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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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EDELWEISS _at_ LSM
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EDWII set-up

• Radiopurity
• dedicated HPGe detectors for systematic checks of
  all materials
• Strict control of bkg material
  selection/cleaning procedure/Environment
• ? Shielding
• 20 cm Pb shielding
• 50 cm PE and better coverage
• active µ veto
• (gt 98 coverage)
• Up to 110 detectors
• -gt 40kg Ge detector
• Ge/NTD
• Develop new ID detectors
• ? Goal EDW-I 100
• sW-n 10-8 pb
• lt0.003 evts/kg/day (Ergt10keV)

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µ-veto
Candidates for coincident veto-bolometer events
Accidental coincidences
Expected from Geant4 simulation 0.03
events/kg.d Measured 0.04
events/kg.d
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Ge Heat-Ionization Detectors

• Simultaneous measurements
• Ionization _at_ few V/cm with Al electrodes
• Heat _at_ 20 mK with Ge/NTD sensor
• Different Ionization/Heat energy ratio for
  nuclear and electronic recoils (dominate bkg)

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Event by event background rejection
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Edw-I limiting background
PRD71, 122002 (2005)
Problem Surface electron recoils

• Interpretation
• Bad charge collection (trapping and
  recombination)
• Indications of 210Pb contamination
• (exposition to Radon)
• a rate e rate
• 4 /kg.day

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210Pb source
210Pb??
210Po??
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GeNTD data improved bkg

• 210Pb-chain background reduction of x2 relative
  to EDELWEISS-I

• Gamma background reduction of x3 relative to
  EDELWEISS-I

Full volume
Conclusion Reduction of background from EDW-I
to EDW-II
Further bkg reductions after fiducial
coincidence cuts
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Physics run GeNTD
Question How to reach lt 10-8 pb ?

• 11 detectors with lt30 keV threshold
• Threshold chosen before start of run
• (EDW-I results ? expected ? bkg)
• 93.5 kg.day
• 3 events observed in nuclear recoil band
• 31, 31 and 42 keV
• Evidence for events with deficient charge
  collection from 210Pb

• NEED
• gt1000 kgd at 15 keV threshold
• gt105 rejection for gammas
• to reject expected gt4000 ? from 210Pb

Preliminary
EDELWEISS 93.5 kgd
IDea Develop detectors with surface event
rejection using interleaved electrode design (ID)
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ID detector

• NTD heat sensor
• E-field modified near surface with interleaved
  electrodes
• BD signals -gt vetos surface
• 1x200g 3x400g tested in2008
• 10x400g running

A electrodes 2V
B electrodes 1V
Z (cm)
guard G 1V
AB near- surface event
AC bulk event
A,BC event in low-field area
guard H - 1V
C electrodes-2V
D electrodes -1V
Radius (cm)
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ID detector rejection

• Gamma rejection of 400g
• 1 month calibrations

• Beta rejection of 200g

6x104 210Po
6x104 210Bi
6x104
?-equivalent to 103 kgd
?-equivalent to 3x104 kgd
0 events
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Physics run ID detectors
Conclusion This is the good technology for 10-8
pb and beyond

• 1 x 400g 1 x 350g detectors, 86 live days
• lt15 keV threshold achieved for exposure of 18.6
  kg.days
• 50 efficiency at 10 keV
• No events in
• (or around) nuclear recoil band

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Limits

• 93.5 kgd GeNTD
• 11 detectors x 4 months
• 30 keV threshold
• 3 events observed in nuclear recoil band
• 18.3 kgd ID
• 2 detectors x 4 months
• 15 keV threshold
• No nuclear recoils
• No evts outside ? band
• 2009 10 ID detectors
• improvement in sensitivity 4x10-8 pb
• More detectors build in 2009

Preliminary
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Conclusions/Outlook

• Significant reduction in ?, ß and ? backgrounds
  relative to EDELWEISS-I
• Improved understanding of backgrounds and of
  response of detectors to backgrounds
• Improved limit relative to EDELWEISS-I
• Passive background reduction alone not sufficient
  to reach lt 10-8 pb
• ID detectors have the surface rejection needed to
  reach this goal

• Running in 2009 with 10 x 400g detectors
• Prototype of ID detectors with larger fiducial
  volumes currently in test
• EURECA 1 ton scale experiment
• (CRESST, EDELWEISS, CERN, ) _at_ LSM
  extension

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This is the end
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Decay Chain
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EDELWEISS-II 210Pb source calibration

• Confirms interpretation of EDW-I bkg as 210Pb
  surface ?.
• Response of detectors to this important background

Edw-II
210Pb??
EDELWEISS-II 210Pb source
210Bi??
Edw-II
210Bi??
210Po??
Edw-II
Edw-I data
206Pb recoils coincident with 210Po ?
?Implantation depth of 210Pb
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EURECA - II
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EURECA-I
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(No Transcript)
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France-Italy Fréjus tunnel new safety gallery
planned
Existing lab
s ?
Existing road tunnel

• 2 projects
• Limited extension
• Very large cavity

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Implantation of new lab
First drawings nov 2006 (Lombardi eng company)
G Gerbier
EURECA ULISSE meeting- Lyon july 2008
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Compatibility DAMA other experiments SI
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Compatibility DAMA other experiments SD
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Present limits
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Experimental data
Number of events in WIMP region qlt 0.5, 25 lt E
lt 60 ??? registered
23 events
Alpha rate 2.5 events
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Estimation of background from 210Pb
460 events
N alphas in calibration spectrum 3040
events Number of events in WIMP region qlt 0.5,
25 lt E lt 60 ??? registered 460 events
Expected number events from calibration with
210Pb 37 events