Status of EDELWEISS-II

Véronique SANGLARDUniversité de Lyon, UCBL1

CNRS/IN2P3/[email protected]

http://edelweiss.in2p3.fr

QuickTime™ et undécompresseur TIFF (non compressé)

sont requis pour visionner cette image.

Status of EDELWEISS-IIStatus of EDELWEISS-II

mailto:[email protected]

http://edelweiss.in2p3.fr/

SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 2

OutlineOutline

EDELWEISS experiment

EDELWEISS-I limits

EDELWEISS-II setup

EDELWEISS-II preliminary results


The EDELWEISS collaborationThe EDELWEISS collaboration CEA Saclay CSNSM Orsay IPN Lyon Institut Néel Grenoble FZ/ Universität Karlsruhe JINR Dubna

*Expérience pour DEtecter Les WIMPs En SIte Souterrain (Underground experiment to detect WIMP)


EDELWEISS @ LSM EDELWEISS @ LSM (Laboratoire (Laboratoire

Souterrain de Modane)Souterrain de Modane)


Heat and Ionization Ge detectorsHeat and Ionization Ge detectors

Simultaneous measurement of

Heat @ 17 mK with Ge/NTD sensor

Ionization @ few V/cm with Al electrodes

Different charge/heat ratio for nuclear recoils (WIMP, neutrons) and electron recoils (, )

EI/ER = 0.3 for nuclear recoils

EI/ER = 1 for electronic recoils

Event-by-event discrimination of electron recoils (main background) Neutrons 73Ge(n,n',) Gammas

IonizationguardIonizatio

ncenter

Fiducial volume(≈ 57%)

Heat

Thermometer(Ge NTD)

Reference electrode

Center electrodeGuard

Electrodes

Ge crystal

Center electrodeGuard ring

7 cmm=320g

Ionization threshold

Amorphous (Ge or Si) ~ 60 nm


EDELWEISS-I EDELWEISS-I (V.S. et al., (V.S. et al., PRD PRD 7171, 122002 (2005)), 122002 (2005))

62 kg.d with 3 detectors Best sensitivity up to

2003, but Background

Neutrons : 1 n-n coincidence observed (2 singles expected by MC)

Surface electron recoils Miscollected charge

events at low energy Leak of events down to

the nuclear recoil band not visible in coincidence events

Rate compatible with 210Pb contamination ( rate ~ 5 / kg.d)




EDELWEISS-II setupEDELWEISS-II setup Cryogenic installation (~ 20 mK)

Reversed geometry cryostat Dilution refrigerator + pulse tube Room for up to 120 detectors

Shielding Clean room + deradonized air

(15 mB/m3) 20 cm Pb 50 cm PE Active veto (> 98% coverage)

Facilities Remotely controlled sources for

calibrations and regenerations Remote operations (cryogeny,

acquisition, …) Detector storage and repair

within the clean room 9 cool-downs since January 2006


EDELWEISS-II setupEDELWEISS-II setup Cryogenic installation (~ 20 mK)

Reversed geometry cryostat Dilution refrigerator + pulse tube Room for up to 120 detectors

Shielding Clean room + deradonized air

(15 mB/m3) 20 cm Pb 50 cm PE Active veto (> 98% coverage)

Facilities Remotely controlled sources for

calibrations and regenerations Remote operations (cryogeny,

acquisition, …) Detector storage and repair

within the clean room 9 cool-downs since January 2006




EDELWEISS-II detectorsEDELWEISS-II detectors

“standard” Ge/NTD bolometers (320 g) as for EDELWEISS-I

Ge/NbSi bolometers (400 g)

“interdigit” Ge/NTD bolometers (200-400 g)


Results from “standard” NTD Results from “standard” NTD detectorsdetectors

Commissioning background run (spring 2007) ~ 19 kg.d 8 lowest threshold detectors selected Only « pure center » events selected for better Ei resolution Reduction of factor 3 of and background

Recoil energy threshold (20-35 keV)

Ion

iza

tio

n/R

ec

oil

Ra

tio

Ion

iza

tio

n/R

ec

oil

Ra

tio



Ion

iza

tio

n/R

ec

oil

Ra

tio

Recoil energy threshold (20-35 keV)

Commissioning background run (spring 2007) ~ 19 kg.d 8 lowest threshold detectors selected Only « pure center » events selected for better Ei resolution Reduction of factor 3 of and background



Significant reduction of the background

Calibration with source (210Pb) to study the detector’s response to surface events

~ 100 kg.d of fiducial exposure accumulated after quality cuts (analysis still underway)




Results from Ge/NbSi detectorsResults from Ge/NbSi detectors

200

150

100

50

0

806040200

x10-3

200

150

100

50

0

806040200

x10-3

Transient

Thermal

Heat signal of thermometer NbSiA :Surface event Bulk event

Thermometer Thermometer NbSiNbSi BB

Thermometer Thermometer NbSi NbSi AA Thermometer Thermometer NbSi NbSi AA


Time (ms)

200

150

100

50

0

806040200

x10-3

200

150

100

50

0

806040200

x10-3

Transient

Thermal





200

150

100

50

0

806040200

x10-3

200

150

100

50

0

806040200

x10-3

Transient

Thermal





Time (ms)

Developed @ CSNSM since 2003 Goal : active identification of

surface events using athermal phonon measurement with NbSi thin film thermometers

Each signal = thermal + athermal component

For surface events, athermal higher in corresponding thermometer

Thermal signals proportional to the deposited energy

Discrimination parameter = asymetry of athermal part of signals from the two surfaces

Surface rejection ok, some problems in 2007 with film contacts / leak currents

Resolutions hasn’t reached Ge/NTD performances


Results from Ge/NbSi detectorsResults from Ge/NbSi detectors Developed @ CSNSM since 2003 Goal : active identification of

surface events using athermal phonon measurement with NbSi thin film thermometers

Each signal = thermal + athermal component

For surface events, athermal higher in corresponding thermometer

Thermal signals proportional to the deposited energy

Discrimination parameter = asymetry of athermal part of signals from the two surfaces

Surface rejection ok, some problems in 2007 with film contacts / leak currents

Resolutions hasn’t reached Ge/NTD performancesData taken with 1 NbSi detector

May & June 2007 ~ 1,5 kg.d fiducial


Results from Ge/Interdigit Results from Ge/Interdigit detectordetector

Radial coordinate (cm)

Z (cm) guard electrode G : + 1V

guard electrode H : - 1V

A electrodes : + 2V B electrodes + 1V

C electrodes : - 2VD electrodes : - 1V

Electrons trajectoriesholestrajectories

A & CBulk event

A , B & CEvent in

low-field area

A & BNear surface

event

Keep the standard phonon detector Modify the E field near surfaces with interleaved

electrodes (6 ionization channels) Use B and D signals as vetos against surface

events From preliminary sea-level measurements

Surface event rejection > 95 % Fiducial volume ~ 50 %



Few kg.d of background runs @ LSM with a 200g detector Performance as expected

(resolutions, threshold, …)

Currently 3 new 400g detectors Precise measurement of

rejection

A promising detector with a simple design

calibration

Neutron calibration

EDELWEISS-IIID-201

EDELWEISS-IIID-201



Few kg.d of background runs @ LSM with a 200g detector Performance as expected

(resolutions, threshold, …)

Currently 3 new 400g detectors Precise measurement of

rejection

A promising detector with a simple designER threshold < 20 keV

No event below Q=0.5

EDELWEISS-IIID-201 (4 kg.d)


Current run (May 2008 - …) Current run (May 2008 - …) Instrumented detectors:

23 “standard” Ge/NTD bolometers

5 “NbSi” bolometers 4 “Interdigit” bolometers

~ 10 kg of GeQuickTime™ et un

décompresseur TIFF (non compressé)sont requis pour visionner cette image.


ConclusionConclusion “standard” Ge/NTD detectors

Improved background understanding : significant reduction of , and backgrounds

100 kg.d recorded and in analysis Ge/NbSi detectors

Surface rejection ok Resolution improvements needed

Ge/Interdigit detectors December 2008 : 9 additional detectors July 2009 : 120 kg.d fiducial exposure with

threshold < 20 keV Up to 35x320g Ge crystals available for

reconfiguration as Ge/Interdigit


EDELWEISS prospectsEDELWEISS prospects 1st Goal :

4x10-8 pb in 2010 Acquire physics data

with 32 Ge/ID

2nd Goal : Few 10-9 pb in 2012 ~ 70 detectors Ge/ID

EURECA (see H. Kraus’s talk next session)

Documents

Status of EDELWEISS-II