eureca – the european cryogenic dark matter search · eureca – the european cryogenic dark...
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EURECA – the European Cryogenic Dark Matter Search
H KrausUniversity of Oxford
Astrophysical Evidence for Dark Matter
Requirements on all Direct Search Experiments
Main Techniques for Large-scale Experiments
CRESST and EDELWEISS
EURECA in itself
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Several astrophysics measurements point to the existence of Dark Matter.
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Direct Detection of WIMPs
WIMP30 < MW [GeV] < 1000
46 > λW [fm] > 1.4
vrms ~ 270 km/s
ρCDM ~ 0.3 GeV / cm3
Heavy Boson Exchange
( ) ( )*W N WR 0
W N
12
41 cos 0.4 keV
GeV
M M ME E
M Mθ= ⋅ ⋅ − ≈ ⋅
+
Direct detection via WIMP scattering by nuclei: ER ~ tens of keV
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WIMP Recoil Energy Spectrum
Underground laboratory• Energy threshold• Shielding• Low radioactivity materials• Event type signature
Few events per kg keV day
Rare event search
Natural radioactivity far too high
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Experiments – MSSM Predictionsσ = 10−6 pb:
~1 event/kg/day~0.1 now reached
σ = 10−8 pb:
~3 events/kg/yearAims of phase II experiments
σ = 10−10 pb:
~30 events/ton/yearNext generation requires further x100 improvement!
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Dark Matter Signatures1.Recoil energy spectrum Energy resolution
exponential, similar to background .
2.Nuclear (not electron) recoils Discrimination is really required now.
3.Coherence: A dependence Multi-target essential once first signal is identified.
4.Absence of multiple interactions Large Array removes some fraction of background.
5.Diurnal modulation nice, but needs low-pressure gaseous target.
6.Annual modulation (requires many events) tricky; most events are close to threshold, small effect.
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Gran Sasso
Depth: 3200 m.w.e.
Surface : 17 300m2
Volume : 180000 m3
Muon flux : 3 10-4 µ.m -2.s-1
Neutrons: 3.8 10-2 n.m -2.s-1
Radon: 50 - 120 Bq/m 3
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DAMA• Data taking completed in July 2002• Total exposure of 107,731 kg.d• See annual modulation at 6.3σ• Claims model-independent evidence
for WIMPs in the galactic halo• 2nd phase: LIBRA 250 kg
2 – 6 keV ee
WIMP candidate, using standard halo parameters:
MΧ = (52 +10) GeV and
σΧ-N = (7.2 +0.4) .10-6 pb-8
-0.9
DAMA / LIBRA running 250 kg; wait at least until 2008 …
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• 25 modules of 9.7 kg• 4 years data taking (09/03 to 07/07)=> 192 000 kg.d = twice DAMA exposure
• From 6 to 8.2σ
9
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Detection TechniquesAr, Xe
ArDM, WARP, XENON, LUX, ZEPLIN
NaIDAMALIBRAANAISNAIAD
GeHDMSGenius-TFIGEXDRIFT
Si, GeCDMSEDELWEISS
Al2O3CRESST I
CaWO4CRESST IIROSEBUD
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Liquid
Gas
E
E
+−
Recoil
S1S2
S1
S2
–10 kV
+7 kV
Taken from T Sumner’s talk at IDM2008
ZEPLIN III (Liquid Noble Gas)
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XENON 10 Results astro-ph:0706.0039Calibration Dark Matter Run 58.6 live days
expected 6.8, seen 10Most liquid noble gas experiments
(ZEPLIN, XENON, WArP, etc) are already recording background and look at ways to remove it.
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ZEPLIN-III Science data847 kg.days continuous exposure Feb/May08 in 12kg liquid
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United KingdomOxford (H Kraus, coordinator)
GermanyMPI für Physik, MunichTechnische Universität MünchenUniversität TübingenUniversität KarlsruheForschungszentrum Karlsruhe
InternationalJINR DubnaCERN
CRESST, EDELWEISS, ROSEBUD + CERN, others
FranceCEA/IRFU SaclayCEA/IRAMIS SaclayCNRS/Neel GrenobleCNRS/CSNSM OrsayCNRS/IPNL LyonCNRS/IAS Orsay
SpainZaragoza
UkraineKiev
The EURECA Collaboration
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Cryogenic Techniques
Initial recoil energy
Displace-ments,
Vibrations
Athermalphonons
Ionization(~30 %)
Thermal phonons(Heat)
Scintillation
(~3 %)
Combination of phonon measurement with measurement of ionization or scintillation
Phonon: most precise total energy measurement
Ionization / Scintillation:yield depends on recoiling particle
Nuclear / electron recoil discrimination.
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Detectors used in CRESSTheat bath
thermal link
thermometer(W-film)
absorbercrystal
Particle interaction in absorber creates a temperature rise in thermometer which is proportional to energy deposit in absorber
Signal pulse (~6keV)
Res
ista
nce
[mΩ
]
normal-conducting
super-conducting
δδδδT
δδδδR
Width of transition: ~1mKSignals: few µ KStablity: ~ µ K
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W-SPTSiliconabsorber
CaWO4
absorber300g
W-SPT
reflecting cavity
140
120
100
80
60
40
20
0
Pulse Height in Phonon Detector [keV]0 20 40 60 80 100 120 140
Pulse Height in Light Detector [keVee]
n
γγγγ and ββββ
QF QF γ, βγ, β =1=1
QF QF αα=5=5
QF QF OO--recoilsrecoils=9=9
QF QF WW--recoilsrecoils=40=40
Phonon – Scintillation
Discrimination of nuclear recoils from radioactive backgrounds (electron recoils) by simultaneous measurement of phonons and scintillation light
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CRESST – Detector Module
CaWO4: h = 40mm, ∅ = 40mm
m = 300g
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CRESST in Gran Sasso
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CRESST Energy Resolution
50
100
150
200
250
300
350
00 20 40 60 80 100 120 140
Kα2
Kα
122keV
136keVKα1
Kβ
Recoil Energy [keV]
Cou
nts
Energy Spectrum of a CRESST detector (“Verena”) – 57Co calibration
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CRESST – Run 30 Result
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α – β/γ Discrimination
Danewich et al – Kiev(116CdWO4 – 330 g, 2975 hrs)
CRESST – LNGS(CaWO4 – 300 g, 633 hrs)
A ‘standard’ scintillator(pulse shape discrim.)
Scintillation part of a phonon – scintillation detector (CRESST)
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α – β/γ Discrimination
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Decay Identification
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Sr
content in crystals / raw m
aterials
0
20
40
60
80
CaCO3 (raw material)
Russia-06 (raw material)
Carat-05
Conrad
China
Ukraine
Russia
Berta
Agnes
Sr concentration ppm
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Targets for rare event searchesCaWO4 – (primary CRESST material): good first choice
ZnWO4 – (additional target): attraction: lower intrinsic radioactivity, potentially higher light yield
CaMoO4– complementary target with ‘better’ quenching factor for nuclear recoils
Al2O3-Ti – bolometer in EDELWEISS setup
0.01 0.1 1 10 1000
10
20
30
40
50
Num
ber
of p
hoto
ns
Temperature (K)
0.01 0.1 1 10 1001
10
100
0
1
2
k21
k12 K, ∆E
k2 k
1
D
Dec
ay ti
me
(µs)
Temperature (K)
)exp()exp(1
)exp(1 21
kT
EK
kT
DkT
Dkk ∆−+
−+
−+=
τ
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Comparison of light yields
0
20
40
60
80
100
120
140
Bi 4G
e 3O12
CaM
oO4
2008
2004
MgF
2
Al 2O
3-T
i
CaF
2
CdW
O4
ZnW
O4
CaW
O4
Rel
ativ
e lig
ht y
ield
, %
300 K 10 K 300 K 10 K
LY of a few targets is already satisfactory, further improvement possible (doping, tuning of growth condition, post-treatment)
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Low-temperature scintillation properties
~504 (integr.)4.2 / 2.9 / 1.7Al 2O3-Ti
~2009 / 54 / 5501.95ZnSe
150±302 / 1382.4Bi 4Ge3O12
41±1142 / 9304.35CaF2
68±201500 / 91003.45MgF2
95±3010 / 3802.3CaMoO4
35±159 /722.4MgWO4
110±252 / 1102.4ZnWO4
1001 / 3402.9CaWO4
LY (8 K), % (photon count)
Decay time, µµµµs
Emission, eV
Crystal
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EDELWEISS – Detectors
Target:Cyl. Ge crystal, 320 gØ 70 mm, h = 20 mmPhonon - signal:NTD-Ge (~ 20 mK)Ionisation - signal:Inner disc / outer guard ring
Volume fiduciel
Phonon
Ionizationgarde
IonizationCentre (+V)
Thermomètre(Ge NTD)
Electrode de Reference
Électrode centre
ElectrodeGarde (+V)
Ge cristale-
trous
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Phonon – Ionisation
252Cf60Co
Excellent resolution in ionisation and phonon signals. Clean γ-calibration data: no event below Q = 0.7.
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New Edelweiss DetectorsInterdigitized Electrode to remove “surface events”
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Edelweiss / EURECA in LSM
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Main hall30 x 10m2 (h 11m)
gamma hall(70 m2)
2 smaller halls(18 m2 and 21 m2)
Double beta decay:NEMO3 Dark matter: EDELWEISS II TGV
Super Heavy nucleus :SHIN TPC sphere
BiPo (SuperNEMO R&D) Low background measurement:
13 Ge low background diodes
Microelectronics logical failure tests
ModaneDepth: 4800 m.w.e.
Surface: 500m2
Volume : 3500 m3
Muon flux : 4.7 10-5 µ.m-2.s-1
Neutrons: 5.6 10-2 n.m-2.s-1
Radon: 15 Bq/m3
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Edelweiss in LSM
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EURECA in LSM
Deepest site in Europe (4800 mwe)
Clean Infrastructure
24 years experience
Central location within Europe
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EURECA in LSM
Timeline:
2009/10: Design Study TDR
2011/12: Digging out of LSM extension begins. In parallel, begin construction of EURECA components away from LSM. Aim for ~100kg stage (10−9 pb).
2014: LSM extension ready to receive EURECA.
2015: Begin data taking and in parallel improve and upgrade.
2018: One tonne target installed.
Existing laboratory
New LSM extension
Possible EURECA Facility Layout
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LSM extension project
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12m
30m
12m
A Possible Facility Layout
A Benoit
Neel Institute
Grenoble
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Experiment Exposure fid kg.d
Expected evtsin ROI
Observed evts
When
Performed
CDMS - Ge 127 0.6 0
Xenon10 - Xe 136 6.8 10
ZEPLIN III -Xe 127 11.6 7
Running/prep
Xenon100 - Xe 3000 to 6000 1 (simu) 2009
CDMS –Ge 200 add’l ? ? ? 2009
Edelweiss - Ge 3000 0.1 (calib) 2011
Backgrounds in Experiments
“Background – free”: improve linearly with exposure
With background: improve like square root of exposure
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~1 evt/kg/day
~3 evt/kg/year
~30 evt/ton/year
Science Results and Aims
Aim of ton-scale experiments
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Status and Long-term FutureEurope:
• Edelweiss / CRESST – current experiments
• EURECA in LSM 2013 / 2014
• Towards 1000 kg ~2016-2018
US:
• CDMS SuperCDMS up to ~16kg at Soudan
• SNOLab ~100 kg (2012+) GEODM
• 1000 kg, similar to EURECA