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/