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From Edelweiss I From Edelweiss I to Edelweiss IIto Edelweiss II

Véronique SANGLARD

CNRS/IN2P3/IPNL

sanglard@ipnl.in2p3.fr

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)

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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