status of edelweiss-ii
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Véronique SANGLARDUniversité de Lyon, UCBL1
CNRS/IN2P3/IPNLyonsanglard@ipnl.in2p3.fr
http://edelweiss.in2p3.fr
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Status of EDELWEISS-IIStatus of EDELWEISS-II
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
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 3
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)
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 4
EDELWEISS @ LSM EDELWEISS @ LSM (Laboratoire (Laboratoire
Souterrain de Modane)Souterrain de Modane)
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 5
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
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 6
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)
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 7
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
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 8
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
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 9
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)
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 10
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
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 11
Results from “standard” NTD Results from “standard” NTD detectorsdetectors
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
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 12
Results from “standard” NTD Results from “standard” NTD detectorsdetectors
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)
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 13
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
Thermometer Thermometer NbSiNbSi BB
Time (ms)
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
Thermometer Thermometer NbSiNbSi BB
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
Thermometer Thermometer NbSiNbSi BB
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
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 14
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
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 15
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 %
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 16
Results from Ge/Interdigit Results from Ge/Interdigit detectordetector
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
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 17
Results from Ge/Interdigit Results from Ge/Interdigit detectordetector
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)
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 18
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
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SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 19
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
SANGLARD V., « Dark Energy and Dark Matter », Lyon, 2008 July 10th 20
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)
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