Edelweiss collaboration

EDELWEISSLatest Results and Future Plans

Edelweiss collaboration:CEA Saclay (IRFU, IRAMIS), CSNSM Orsay (CNRS/IN2P3 + Univ. Paris Sud), Karlsruhe Institute of

Technology (IEKP, IKP, ITP), Institut Néel Grenoble (CNRS/INP), IPN Lyon (CNRS/IN2P3 + Univ. Lyon 1), Laboratoire Souterrain de Modane , JINR Dubna , University of Oxford , University of Sheffield

Hans Kraus, University of Oxford

on the behalf of the EDELWEISS collaboration

Karlsruhe – Oct.2009 Oxford – Sept. 2010

J. Gironnet - IPNL - Patras 2011

Expérience pour DEtecterLes Wimps En SIteSouterrain

• Search for WIMP dark matter (scattering:~10keV nuclear recoil with <0.01 events/kg/day)

• Need:

• Sensitive Detectors (cryogenic germanium phonon-ionization detectors)

• Low background (passive shielding and ultra-low background materials)

• Excellent background discrimination(active rejection by muon vetoing and surface event identification)

• Extended running periods / stability(good cryostat performance and calibrations)

• Laboratoire Souterrain de Modane

� Place: Laboratoire Souterrain de MODANEcosmic muon flux: 4 µ/m2/day

� Cryogenic installation (18 mK):� Reversed geometry cryostat, pulse tubes� Remotely controlled� Can host up to 40kg of detectors

� Shieldings:� Clean room + de-radonized air� Active muon veto (>98% coverage)� 50-cm PE shield� 20-cm lead shield

� Other items :� Remotely controlled sources for gamma

calibrations + regenerations� AmBe sources of neutron calibrations� Radon detection down to few mBq/m3

�3He neutron detector (thermal neutron monitoring inside shields) sensitivity ~10−9

n/cm2/s� Liquid scintillator neutron counter (study of

muon-induced neutrons)Global setup view

The EDELWEISS-II infrastructure

FRANCE ITALIE

AltitudesDistances

1228 m 1298 m1263 m0 m 6210 m 12 868 m

4800 mwe

3

EDELWEISS I – Detectors

Target:Ge crystalPhonon - signal:NTD-Ge (~ 20 mK)Ionisation - signal:Inner disc / outer guard ringfew V/cm

� Event by event background discrimination

� Limitation: surface events









EDELWEISS II InterDigit (ID) detectors

Bulk events: charge only on fiducial

electrodes (A & C)

A: +4 V

B: −1.5V

C: −4 V

D: +1.5VSurface event (β)

rejection: 105

Surface events:charge on veto electrodes

(B, D, guard rings)

A. Broniatowski et al Phys Lett B 681 (2009) 305 [arXiv:0905.0753]

ID detectors – surface event rejection

A. Broniatowski et al Phys Lett B 681 (2009) 305 [arXiv:0905.0753]

Surface event (β) rejection: 6×10–5

(90% CL)

210Pb Calibration

6×104 β events

WIMP search: final results

Five WIMP candidates:- 4 evts: 20.8 < E < 23.2 keV- 1 evt @ 172 keV

alpha tail

fiducial volume events, 427 kg.d

• Gamma background – 1.8×104 events (20-200keV) 133Ba calibrations → 3×10−5 leakage into NR band

→ <0.9 events

• Surface events – 5000 events, rejection factor 6×10−5

→ 0.3 events

• Muon induced events missed by veto → <0.4 events

• Neutrons from rock – GEANT4 simulations → <0.11 events

• Neutrons from contaminants in shield/cryostat → <0.21 events

• Neutrons from connectors / cabling in cryostat → <1.1 events

Edelweiss II Background estimate

Total background estimate: 3.0 events

EDELWEISS II ResultsPreliminary result: Physics Letters B 687 (2010) 294-298

Final result: Accepted for publication in Physics Letters B. [arXiv:1103.4070v2]

[CDMS December 2009 result: 3.8×10-8pb, 2 nuclear recoil events]

• Run April 2009 - May 201014 months of continuous operation@ 20mK (85% duty cycle)

• 10 x 400g ID Ge detectors, 384kg day

• 4.4×10-8pb excluded for 85GeV WIMP

• Five nuclear recoil events (above20keV analysis threshold)

• Background estimate: 3.0 events

Results – inelastic scattering

• WIMP-nucleus scattering → excited state

• Mass splitting δ~120keV, DAMA region excluded above 90GeV

Elastic WIMP scattering limits: similar sensitivitiesfrom CDMS and EDELWEISS

arXiv:1103.4070Limits very close, with same target nucleus: why not combine data?

� “Simple merger method”

� More sophisticated ones also used in paper

� Strong and efficient collaboration allowed completion of analysis within few months

CDMS+EDELWEISS: the data

CDMS+EDELWEISS: the limits

EDELWEISS III: new detectors FID800 (2010)

• All fiducial volume: more statistics than stackedID-400 statistics

• No event in NR

• Expected to be and isindeed better than IDs!

Preliminary

ID (350000 γ)

Fiducialmass~600g

Towards 5×10−9 pb: EDELWEISS III

Programme under way, funded.

Detector improvements:

• ~40 FID800 detectors to be installed early 2012: 24kg fiducial

• 2 NTD heat sensors (better heat ch), 4 ionization channels, instead of 6.

Infrastructure improvements:

• Within the Edelweiss-II setup –upgrades of cryogenics, cabling, DAQ, shielding.

• Extra internal PE shield.

• Dark matter experiment, to search for WIMP interactions to σ~10-10pb (~1 event/tonne/year)

• CRESST and EDELWEISS, and additional groups

• Cryogenic (<100mK) calorimeters

• Multiple target materials: Ge, CaWO4, ZnWO4….

• Mass: above 100 kg towards 1 tonne

European Underground Rare Event Calorimeter Array

Indication, Confirmation, Study

XENON 100

CDMSEDELWEISS

ZEPLIN III (FSR)

100 kg – 1000 kg projections

Timeline:

2010/2011: Design Study � TDR

2011/12: Digging at LSM. Machine starts Sept 2011 at 20m/d. Begin construction of EURECA components away from LSM. Aim for ~150kg stage (10−9 pb).

2014: LSM extension ready to receive EURECA.

2015: Begin data taking and in parallel improve and upgrade.

2018: One tonne target installed.

Spokesman: Hans Kraus (2005-2010), since January 2011: Gilles Gerbier

Existing laboratory

Summary

• Edelweiss-II: Direct WIMP search with cryogenic germanium detectors

• Interleaved electrodes allow surface event rejection

• Ten 400 g Ge-ID detectors – 384 kg day• 4.4×10-8 pb excluded for 85 GeV WIMP• Nuclear recoils: 5. • Expected background: 3. (gamma, beta leakage,

neutrons from cosmic muons, radioactivity)• …Edelweiss-III (5×10-9 pb)….EURECA (10-10 pb)

Documents

Edelweiss collaboration