from edelweiss i to edelweiss ii
DESCRIPTION
Véronique SANGLARD CNRS/IN2P3/IPNL [email protected] http://edelweiss.in2p3.fr. From Edelweiss I to Edelweiss II. Outline. The Edelweiss-I experiment 2003 results Ionization trigger data taking Phonon trigger data taking The second phase : Edelweiss-II - PowerPoint PPT PresentationTRANSCRIPT
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From Edelweiss I From Edelweiss I to Edelweiss IIto Edelweiss II
Véronique SANGLARD
CNRS/IN2P3/IPNL
http://edelweiss.in2p3.fr
V.SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 2
Outline
The Edelweiss-I experiment
2003 results Ionization trigger data taking Phonon trigger data taking
The second phase : Edelweiss-II
Perspectives and conclusion
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The Edelweiss* collaboration
CEA-Saclay DAPNIA/DRECAM CRTBT Grenoble CSNSM Orsay FZK/Univ. Karlsruhe IAP Paris IPN Lyon Laboratoire Souterrain de Modane
1700 m depth under the Fréjus tunnel (4800 we)
4 µ/m²/d (106 less than at the surface)*Expérience pour DEtecter Les WIMPs En SIte Souterrain (Underground experiment to detect WIMP)
V.SANGLARD Identification of Dark Matter 2004 Edinburgh 07/09/04 4
Heat and ionization detectors
Simultaneous measurement ofcharge and heat signals for eachinteraction
Different charge/heat ratio for nuclear and electron recoils(γs, βs ionize more than WIMPs and neutrons)
Event by event discrimination
Neutrons 73Ge(n,n',γ) Gammas
Ionization threshold
Discrimination > 99.9 % for Erec>15 keV
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Charge collection
Miscollected charge events can simulate nuclear recoilsUse of gamma calibration (57Co, 137Cs) to check the detector charge collection quality Few miscollected charge events with amorphous layerSince 2002 use detectors with amorphous layer
WITH
WITHOUT
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The 1 kg stage
Shield : 30 cm paraffin 15 cm lead 10 cm copper
Ge or Si amorphous layer Guard ring
fiducial vol. : 57 %**(O.Martineau et al. Nim A in press)
NTD heat sensor
Al sputteredelectrodes
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2003 Edelweiss data Additional ~45 kg.d recorded with 3
new detectors 2 phases with 2 different triggers
On the ionization signal On the phonon signal
2000-2003 data represent ~ 62 kg.d
Results : Events observed in nuclear recoil band
(40 for Erec > 15 keV)
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2003 data (ionization trigger)
20 kg.d
Energy threshold : 20, 30 keV
3 events observed in the nuclear recoil band (above these thresholds)
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2003 data (phonon trigger)
Lower energy threshold : 15 keV
18 events observed in nuclear recoil band, most (12) below 30 keV in 22 kg.d
1 coincidence n-n observed between detectors (10% prob.)
Stable behavior of 3 detectors over total exposition
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Edelweiss new limit
Unknown backgrounds
"Yellin method"* used to derive
exclusion limit *(PRD 66,032005 (2002))
No background subtraction
New (prel.) limit consistent with the previous publication*
*(Phys. Lett. B 545 43 (2002))
PRELIMINARY
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Experimental spectrum
Low energy spectrum inconsistent with Wimp mass > ~ 20 GeV
Possible backgroundsNeutrons (n-n coinc.)Miscollected charge
events (surface events)
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Lessons from Edelweiss-I
With 3 new detectors and an extended exposure, the preliminary 2003 exclusion limit confirms the previous published one
Surface events : Improved radiopurity in Edelweiss-II Identification (or suppression) possible with
NbSi thin film sensor Neutron background :
Improved shielding against neutron Anti-coincidences more efficient with
increased number of detectors
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Identification of surface events
2 NbSi athermal phonon sensors for surface event rejection
Two components : Thermal (energy) Athermal/transitory
(near-surface tag) For this surface event,
the athermal component is higher in NbSi 1
First tests of 200g modules in Edelweiss-I promising :
10 x less background while retaining 50 % efficiency
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Perspectives : Edelweiss-II Aim : x 100 improvement in
sensitivity 1st phase :
21*320g Ge bolometers with NTD heat sensor
7*400g Ge bolometers with NbSi thin film sensor
Installation started in April 2004 Data taking in 2005
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Edelweiss II : new cryostat
Larger experimental volume
Low radioactivity cryostat
Innovative reversed geometry
10 mK base temperature
First phase : 28 detectors, up to 120
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Edelweiss II : new setup
Clean room Efficient shielding
against neutron and gamma ray background
20 cm lead 50 cm PE Muon veto
Sensitivity Edelweiss I :
0.2 evt/kg/day Edelweiss II :
0.002 evt/kg/day
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Conclusion 2003 preliminary data confirm the 2002
exclusion limit Edelweiss-I is sensitive to -optimistic-
SUSY models (10-6 pb) Edelweiss-II, goals :
To reach more favored SUSY models (10-8 pb) Competitive with CDMS-II, CRESST-II
Testing the bulk of SUSY parameter space (>10-10 pb) will require one-ton detector array and an extreme background rejection