EDELWEISS-I last results EDELWEISS-II prospects for dark matter direct detection

1. EDELWEISS-I last results EDELWEISS-II prospectsfor dark matter direct detection CEA-Saclay DAPNIA and DRECAMCRTBT GrenobleCSNSM OrsayIAP ParisIPN LyonModane Underground Laboratory (Fréjus) FZ-Karlsruhe and Univ. Karlsruhe B. Censier, CSNSM Orsay, France for the EDELWEISS collaboration Astroparticle Montpellier Toulouse meeting - 29/04/2005

2. Direct detection constraints • Spherical dark matter halo • Elastic scattering on target nucleus • a few 10s keV deposited • Rare events (< 1 evts/kg/day) • Low background environment: • Underground laboratory • Passive and active shielding • Low radioactivity Materials • High target mass & Long time run (>year) • Experimental signatures: • Annual or daily modulation • Comparison of several absorbers • Active discrimination of radioactive background Edelweiss detectors environment

3. Ge IGEX(US/Russ) HDMS(Ger/Russ) Ge, Si EDELWEISS (Fr/Ger) CDMS (US) Liquid Xe Al2O3,LiF ZEPLIN (GB) XENON (US) XMASS (Jap) CaWO4, BGO NaI, Xe CRESST(Ger) Rosebud(Spa/Fr) DAMA (Italie) Detection methods WIMP ≈ 20 % energy Ionization absorber Heat ≈ 100% energycryogenic detectors Light ≈ few % energy

4. Heat and ionisation detectors 320g high purity Ge detectors « Centre » Ionisation channel « Guard » Ionisation channel electrons Ge E heat channel Wimp NTD sensor holes Scattered Wimp • Ionisation: some thousands pairs over some 100ns • 2 Al sputtered electrodes (Centre+Guard) • Heat: some µK over ms • Neutron Transmutation Doped thermistor

5. Event by event discrimination Neutron source calibration Gammas, electrons Electron recoils Neutrons, WIMPs Nuclear recoils 73Ge(n,n’,) Ionisation theshold • Different heat/charge ratio for electron and nuclear recoil • Discrimination>99.9% for Erecoil>15keV

6. Edelweiss-I 1kg stageWhat’s new ? Energy threshold improvement • previous 2003 results: 3320g detectors, additional 20kg.day fiducial exposure with ionisation trigger (100% efficiency for Erec>30keV) • latest results (preliminary): additional 22.66kg.day fiducial exposure with phonon trigger (100% efficiency for Erec>15keV)

7. Wimp-nucleon cross-section constraints(Spin-independent) • Sensitivity confirmed with 61.8 kg.d total exposure • DAMA candidate excluded at 99.8% CL for Mwimp44GeV • Model independent exclusion • Copy & Krauss, Phys.Rev.D67, 2003 • Kurylov & Kamionkowski, phys.Rev.D69, • 2004 DAMA candidate EDELWEISS-I last results: astro-ph/0503265

8. Wimp-nucleon cross-section constraints(Spin-dependent) • Two types of coupling to matter to be considered: • Scalar coupling (spin-independent) (mass number)2  dominant for heavy nuclei • Axial-vector coupling (spin-dependent) nuclear spin (from unpaired proton or neutron) • 7.8% of natural Ge is 73Ge, a high-spin isotope • 4.8kg.day of exposure for spin-independent interaction • Even with high-spin nuclei, direct detection sensitivity is orders of magnitude lower for spin-dependent

9. Wimp-nucleon cross-section constraints(Spin-dependent) Sensitivity of EDELWEISS to spin-dependent interactions: astro-ph/0412061 • Low 73Ge content balanced by nuclear recoils discrimination and high neutron nuclear spin • Indirect detection still 10 times more sensitive (Baksan, Super-K)

10. EDELWEISS-II • 100 liter cryostat for up to 120 detectors : ≈ 36 kg Ge • Improve sensitivity by factor ~100 • EDELWEISS I: ~0.2evt/kg/day (~10-6pb) • EDELWEISS II: ~0.002evt/kg/day (~10-8pb) • Assembly in progress • First data taking: september 2005 Reversed cryostat, base Temperature: 10mK Close packed detectors (hexagonal arrangement)

11. EDELWEISS-IIimproved background rejection • EDELWEISS-I • 2 main limitations: • neutron background • Miscollected near-electrode events • EDELWEISS-II • 2 main improvements: • muon veto + improved shielding: 20cm lead, 50cm PE • near-electrode events identification

12. Transitory thermal 200 Heat signal NbSi 1 NbSi 2 150 100 50 0 0 20 40 60 80 Time (a.u.) -3 x10 Near-electrode events identificationwith NbSi bolometers • Thin evaporated NbSi layers near metal/insulator transition developped at CSNSM Orsay • Good coupling with Ge absorber allows out-of-equilibrium phonons detection • Simultaneous charge measurement by Nb electrodes • Near-electrodes events have an enhanced transitory part NbSi 1 Near electrode event NbSi 2 Mirabolfathi et al., 2001

13. Near-electrode events identificationwith NbSi bolometers 57Co calibration run Same run, cut on transient pulse Q=Ei/Er Er(keV) Er(keV) • Efficient method down to threshold energy • Qualification in Modane: rejection:25% of events, 83% of low-Q events • Further improvements: better energy resolution, reproducibility • 7 NbSi bolometers in EDELWEISS-II first phase

14. 10 8 6 Signal (mV) 4 2 0 -800 -400 0 400 800 Time (ns) Near-electrode events identificationwith ionisation channel • Time-resolved ionisation measurements + carrier transport simulation code allows position identification • 1mm resolution @122keV on test detectors • Further improvement: High Electron Mobility Transistor at 4K  event 122keV Experimental signal Holes collected Best fit by simulation Induced charge(A.U) Electrons collected Time (ns) Broniatowski et al., 2001 • Other applications: • Double-beta decay • Studies on: Electronic transport, space-charge, quality of charge collection

15. CDMS, CRESSTEDELWEISS-I present (~0.1 event/kg/day) CDMS-II, CRESST-II, EDELWEISS-II,XENON, XMASS sensitivity goals (~a few events/ton/day) 1 Ton sensitivity goal (optimistic) (~a few events/ton/year) L. Rozkowski et al., hep-ph/0208069 Conclusion • Say good bye to EDELWEISS-I • Understanding the background • R&D work on detectors • European (Eureca) and american (Super CDMS) projects for 1 ton target