EDELWEISS-I last results EDELWEISS-II prospects for dark matter direct detection CEA-Saclay DAPNIA and DRECAM CRTBT Grenoble CSNSM Orsay IAP Paris IPN Lyon Modane Underground Laboratory (Fréjus) FZ-Karlsruhe and Univ. Karlsruhe B. Censier, CSNSM Orsay, France for the EDELWEISS collaboration Astroparticle Montpellier Toulouse meeting - 29/04/2005

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

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

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

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

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

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

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 73 Ge, 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

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

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

EDELWEISS-II improved 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

Near-electrode events identification with NbSi bolometers NbSi 1 NbSi 2 Near electrode event 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 x10 -3 Transitory thermal Time (a.u.) Heat signal NbSi 1 NbSi 2 Mirabolfathi et al., 2001

Near-electrode events identification with NbSi bolometers 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 57 Co calibration run Same run, cut on transient pulse Er(keV) Q=Ei/Er

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

Conclusion Say good bye to EDELWEISS-I Say good bye to EDELWEISS-I Understanding the background Understanding the background R&D work on detectors R&D work on detectors European (Eureca) and american (Super CDMS) projects for 1 ton target European (Eureca) and american (Super CDMS) projects for 1 ton target 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) CDMS, CRESST EDELWEISS-I present (~0.1 event/kg/day) L. Rozkowski et al., hep-ph/