EDELWEISS Latest Results and Future Plans

Hans Kraus, on the behalf of the University of Oxford EDELWEISS collaboration

Karlsruhe – Oct.2009 Oxford – Sept. 2010

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 J. Gironnet - IPNL - Patras 2011 Expérience pour DE tecter Les Wimps En SI te Souterrain • 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 The EDELWEISS-II infrastructure

Place: Laboratoire Souterrain de MODANE FRANCE ITALIE cosmic muon flux: 4 /m 2/day

4800 mwe
Cryogenic installation (18 mK):  Reversed geometry cryostat, pulse tubes Altitudes 1228 m 1263 m 1298 m Distances 0 m 6210 m 12 868 m 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 3  Radon detection down to few mBq/m 3  He neutron detector (thermal neutron monitoring inside shields) sensitivity ~10 −9 n/cm 2/s  Liquid scintillator neutron counter (study of Global setup view muon-induced neutrons) 3 EDELWEISS I – Detectors

Target: Ge crystal Phonon - signal: NTD-Ge (~ 20 mK) Ionisation - signal: Inner disc / outer guard ring few V/cm

 Event by event background discrimination

 Limitation: surface events EDELWEISS I – Detectors

Target: Ge crystal Phonon - signal: NTD-Ge (~ 20 mK) Ionisation - signal: Inner disc / outer guard ring few V/cm

 Event by event background discrimination

 Limitation: surface events EDELWEISS I – Detectors

Target: Ge crystal Phonon - signal: NTD-Ge (~ 20 mK) Ionisation - signal: Inner disc / outer guard ring few V/cm

 Event by event background discrimination

 Limitation: surface events EDELWEISS II InterDigit (ID) detectors

A: +4 V B: −1.5V

C: −4 V D: +1.5V Surface event ( β) rejection: 10 5 Bulk events: Surface events: charge only on fiducial charge on veto electrodes electrodes (A & C) (B, D, guard rings)

A. Broniatowski et al Phys Lett B 681 (2009) 305 [arXiv:0905.0753] ID detectors – surface event rejection

210 Pb Calibration 6×10 4 β events

Surface event ( β) rejection: 6×10 –5 (90% CL)

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

fiducial volume events, 427 kg.d

alpha tail

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

• Gamma background – 1.8 ×10 4 events (20-200keV) 133 Ba 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

Total background estimate: 3.0 events EDELWEISS II Results

Preliminary result: Physics Letters B 687 (2010) 294-298 Final result: Accepted for publication in Physics Letters B. [arXiv:1103.4070v2 ]

• Run April 2009 - May 2010 14 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 (above 20keV analysis threshold) • Background estimate: 3.0 events [CDMS December 2009 result: 3.8 ×10 -8pb, 2 nuclear recoil events] Results – inelastic scattering

• WIMP-nucleus scattering → excited state • Mass splitting δ~120keV, DAMA region excluded above 90GeV Elastic WIMP scattering limits: similar sensitivities from CDMS and EDELWEISS

Limits very close, with same target nucleus: why not combine data? arXiv:1103.4070 CDMS+EDELWEISS: the 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 limits EDELWEISS III: new detectors FID800 (2010)

Fiducial mass ~600g

• All fiducial volume: more Preliminary statistics than stacked ID-400 statistics • No event in NR • Expected to be and is indeed better than IDs!

ID (350000 γ) 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. European Underground Rare Event Calorimeter Array Indication, Confirmation, Study

• Dark matter experiment, to

search for WIMP interactions R) ISS (FS WE -10 III EL to σ~10 pb LIN ED MS EP CD (~1 event/tonne/year) Z • CRESST and EDELWEISS, and 0 additional groups 10 ON EN • Cryogenic (<100mK) X s ion calorimeters ject pro • Multiple target materials: kg 000 – 1 Ge, CaWO 4, ZnWO 4…. kg 100 • Mass: above 100 kg towards 1 tonne Timeline: 2010/2011: Design Study  TDR 2011/12: Digging at LSM. Machine starts Sept 2011 at 20m/d. Begin Existing laboratory 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 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)