EDELWEISS-I last results EDELWEISS-II prospects for dark matter direct detection
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Transcript of EDELWEISS-I last results EDELWEISS-II prospects for dark matter direct detection
EDELWEISS-I last results EDELWEISS-II prospects
for 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
Direct detection constraints• Spherical dark matter halo
• Elastic scattering on target nucleusa 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
HeatHeat
IonizationIonization
LightLight
≈ few % energy
≈ 20 % energy
≈ 100% energycryogenic detectors
absorberabsorber
GeGe
NaI, XeNaI, Xe
Al2O3,LiFAl2O3,LiF
DAMA (Italie)
IGEX(US/Russ) HDMS(Ger/Russ)
Liquid XeLiquid Xe
Ge, SiGe, Si
CaWO4, BGOCaWO4, 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
Wim
p
NTD sensor
electrons
holes
heat channel
« Centre » Ionisation channel
• IonisationIonisation: some thousands pairs over some 100ns • 2 Al sputtered electrodes (Centre+Guard)
• HeatHeat: some µK over ms
• Neutron Transmutation Doped thermistor
320g high purity Ge detectors
Ge
« Guard » Ionisation channel
E
Event by event discriminationNeutron source calibration
73Ge(n,n’,)
Ionisation theshold
Neutrons, WIMPsNuclear recoils
• Different heat/charge ratio for electron and nuclear recoil
• Discrimination>99.9% for Erecoil>15keV
Gammas, electrons
Electron recoils
Edelweiss-I 1kg stageWhat’s new ? Energy threshold improvement
• previous 2003 results:previous 2003 results: 3320g detectors, additional 20kg.day fiducial exposure with ionisation trigger (100% efficiency for Erec>30keV)
• latest results (preliminary):latest results (preliminary): additional 22.66kg.day fiducial exposure with phonon trigger (100% efficiency for Erec>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 Mwimp44GeV
• Model independent exclusionCopy & Krauss, Phys.Rev.D67, 2003Kurylov & Kamionkowski, phys.Rev.D69, 2004
DAMA candidate
EDELWEISS-I last results: astro-ph/0503265
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
Wimp-nucleon cross-section constraints (Spin-dependent)
• Low 73Ge 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/0412061
EDELWEISS-II• 100 liter cryostat for up to 120 detectors : ≈ 36 kg Ge100 liter cryostat for up to 120 detectors : ≈ 36 kg Ge• Improve sensitivity by factor ~100Improve sensitivity by factor ~100
• EDELWEISS I: ~0.2evt/kg/day (~10-6pb)• EDELWEISS II: ~0.002evt/kg/day (~10-8pb)
• Assembly in progressAssembly in progress• First data taking: september 2005First data taking: september 2005
Reversed cryostat, base Temperature: 10mK Close packed detectors
(hexagonal arrangement)
EDELWEISS-IIimproved background rejection
EDELWEISS-IEDELWEISS-I 2 main limitations:2 main limitations:
• neutron background
• Miscollected near-electrode events
EDELWEISS-IIEDELWEISS-II 2 main improvements:2 main improvements:
• muon veto + improved shielding: 20cm lead, 50cm PE
• near-electrode events identification
Near-electrode events identificationwith 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
200
150
100
50
0
806040200
x10-3
200
150
100
50
0
806040200
x10-3
Transitory thermal
Time (a.u.)
Heat signal NbSi 1NbSi 2
Mirabolfathi et al., 2001
Near-electrode events identificationwith 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
57Co calibration run Same run, cut on transient pulse
Er(keV) Er(keV)
Q=
Ei/
Er
Near-electrode events identificationwith ionisation channel
10
8
6
4
2
0
Sign
al (
mV
)
-800 -400 0 400 800Time (ns)
event 122keV
Experimental signal
Best fit by simulation
Electrons collected
Holes collected
Indu
ced
char
ge(A
.U)
Time (ns)Broniatowski et al., 2001
• 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
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 backgroundUnderstanding the background
• R&D work on detectorsR&D work on detectors
• European (Eureca) and american European (Eureca) and american (Super CDMS) projects for 1 ton (Super CDMS) projects for 1 ton targettarget
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, CRESSTEDELWEISS-I present(~0.1 event/kg/day)
L. Rozkowski et al., hep-ph/0208069