Edelweiss-II : status and first results A new generation of background-free bolometers for WIMP...

Edelweiss-II : status and first results

A new generation of background-free bolometers for WIMP search

X-F. Navick - CEA Saclay, IRFU, France

LTD13 – Stanford July 24th 2009

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Direct search for WIMPs with cryogenic detectors

astro-ph/08054705

KIMS

EDELWEISS-I

CRESST-II

CDMS-IIXENON

WIMPs forming our Galactic halo• 10 - 1000 GeV mass• v ~ 200 km/s ⇒ 0-50 keV nuclear recoils

(~ exponential spectrum)

SUSY neutralino (σ prediction)• <1 collision / kg / month

Cryogenic 10mK phonon/ionization detectors :

Detector requirements on both channelslow thresholdsexcellent discrimination between populationsbackground and signal identification

Xe

Ge

Navick - LTD13 - Stanford - July 09

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Phonon-ionization « NTD » sensors type

Edelweiss-I detectors Ionization measurement @ few V/cm Heat measurement (NTD sensor) @ 20

mK Discrimination between electron and

nuclear recoils Q ~ ionization/heat

« NTD » type : plain Al electrodes


4

Edelweiss I results and limits (2005)

Bad charge collection

Pb210 calibration

Charge collection deficit of electron like events : « surface » events Demonstrated 210Pb origin by calibration with 210Pb source


5

The Edelweiss-II experiment

Operated at the Underground Laboratory of Modane, 4800 mwe (4μ/day/m2)

Cryogenic installation (~ 20 mK) : Reversed geometry cryostat Use of pulse tubes

Can house up to 40 kg of detectors Shielding :

Clean room + deradonized air Active muon veto (>98% coverage) 50 cm PE shield, 20 cm Lead shield

⇒ γ background reduced by ~2 wrt EDW1 Facilities :

Remotely controlled sources for calibrations + regenerations

Detector storage & repair within clean room

12 cool-downs already operated


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The muon veto in action

Ioni

zatio

n/re

coil

ratio

• Geant4 - expected : ~0.03 evts / kg.d• Mostly nuclear recoils below 50 keV

• Measured bolometer - muon veto coincidence rate : ~ 0.04 evts/kg.d

• The ionization yield distribution of coincidences is consistent with muon-induced events

2007-2008 data (280 kg.d - no cut)

spectra

• In addition: neutron detector installed to study induced n with higher stats

• Interactions in detectors due to muon-induced neutrons inside the shields


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Physics run with « NTD » detectors

210Pb

210Po

206Pb

β

EDELWEISS-II93.5 kgd

Beta radioactivity at the surface of detectors• Incomplete charge collection• « Leakage » of such events down to the nuclear recoil region• Beta bkg reduced wrt EDW-I but stillinsufficient to reach 10-8 pb

EDW-II 2008 data :• 11 NTD detectors with < 30keV thresholds• 94 kg/d in 4 months• Threshold chosen a priori• =>3 events in nuclear recoil band


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Surface event rejection : interleaved electrodes

‘b’ electrodes (+4V)

collecting‘a’ electrodes (-1.5V)

field shapping « VETO »

‘d’ (-4V) ‘c’ (+1.5V)

• Keep the EDW-I phonon sensor• Modify the E field near the surfaces with interleaved electrodes • Use ‘a’ and ‘c’ signals as vetos against surface events

First detector built 20071x200g + 3x400g tested in 200810x400g running since spring 2009

« ID » (interdigit) detector

Volume Guard

Surface


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An outstanding surface event discrimination

Beta calibration(210Pb)200g detector

« single-side » surface events E1=0

« 3-electrode » surface events

46 keV gamma ray line

fiducial volume events

• Surface and volume events are completely separated !• From β calibration : overall rejection ~ 1/105

Preliminary


2

• A combination of cuts is madeon the signals of electrodes• Example here : cut on the difference of signals between 2 collecting electrodes

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IDs : overall background rejection performances

0 events

-equivalentto ~103 kgd

-equivalentto 3x104 kgd

arXiv:0905.0753


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ID fiducial volume : background data

400g detector, background run

Fiducial volume cut

Preliminary

σion = 300 eV


• Cosmogenic 68Ge, 65Zn lines @ 10 keV

• Background electron recoilsare homogeneously distributed in the volume of the crystal

• Fiducial volume = 160g, primarily limited by the guard regions

• Approx. ~ 20 kg.d of background data with two 400g detectors (2008 data)

2

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Physics run with IDs

2008 : • 86 live days / 4 months / 2x400g detectors• 18.3 kg.d with < 15 keV threshold, ~50% eff at 10keV

2009 : physics run ongoing• 10 detectors running (2kg fiducial)• x 20 improvement by 2010 : 4x10-8 pb• Additional new detectors w increased fiducial volume (« FIDs » 400g, 800g) => 9 kg fiducial mass end 2010

Background free

Preliminary


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The future : EURECA

EURECA : beyond 10-9 pb, major efforts

in background control and detector

development

Joint effort from teams from

EDELWEISS, CRESST, ROSEBUD,

CERN, +others…

100 kg-1T cryogenic experiment, multi-

target : scintillators and Germanium

Part of ASPERA European Roadmap

Preferred site: 60 000 m2 extension of

present LSM (4 /m2/d), to be dig in

2011-2012

Design study start by end year

Start installation by 2013

Actual lab

Projected lab

EURECA : 2 cryostats in water tanks


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Summary

Edelweiss-II now aiming at ~ 10-8 pb

Neutron shield and muon veto designed for < 10-8

New generation of « ID » detectors are validated Robust fabrication and operation Thresholds <15 keV Electron recoil rejection and surface event rejection (~1/105) Good fiducial volume - with improvements ongoing

ID detectors are well-fitted for future 100kg / ton-scale bolometric dark matter searches


CEA Saclay (IRFU and IRAMIS) Detectors, electronics, acquisition, background, analysis E. Armengaud, O. Besida, G. Gerbier, M. Gros, X-F. Navick, B. Paul, S. Hervé, M. Karolak, (M. Chapellier), P.Pari Post-doc: M Hannawald Thesis : A. Chantelauze (cotutelle FZK), J Domange BDI CNRS, CSNSM Orsay Detectors, cabling, cryogenics, analysisL. Berge, A. Broniatowski, D. Carré, S. Collin, L. Dumoulin,, F. Lalu, S. MarnierosPost-doc/ATER : E. Olivieri Thesis : O. Crauste, J Domange CNRS IPN Lyon Electronics, background, analysis, detectorsC Augier, F. Charlieux, M. De Jésus, P. Di Stefano, J. Gascon, A. Juillard, V. Sanglard, L. Vagneron,

Thesis : M. Luca, S. Scorza CNRS I Néel Grenoble Cryogenics, electronicsA. Benoit, M. Caussignac, H. Rodenas FZ/ Universität Karlsruhe Muon Veto and neutron counter, backgroundJ. Blümer, K. Eitel, Thesis : H. Kluck, A. Chantelauze (cotutelle FZK)Post doc : V Koslov JINR Dubna Monitoring of neutron and radon backgroundsE. Yakushev, S. Semikh Thesis : A. Lubashevski, L. Perevozchikov Oxford University High impedance sensors, wiring H. Kraus, S Henry, V Thesis : S Kierkby,

The Edelweiss IIcollaboration


Edelweiss-II : status and first results A new generation of background-free bolometers for WIMP...

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