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

Several astrophysics measurements point to the existence of Dark Matter.

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

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

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!

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.

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

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 …

• 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

Detection TechniquesAr, Xe

ArDM, WARP, XENON, LUX, ZEPLIN

NaIDAMALIBRAANAISNAIAD

GeHDMSGenius-TFIGEXDRIFT

Si, GeCDMSEDELWEISS

Al2O3CRESST I

CaWO4CRESST IIROSEBUD

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)

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.

ZEPLIN-III Science data847 kg.days continuous exposure Feb/May08 in 12kg liquid

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

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.

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

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

CRESST – Detector Module

CaWO4: h = 40mm, ∅ = 40mm

m = 300g

CRESST in Gran Sasso

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

CRESST – Run 30 Result

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)

α – β/γ Discrimination

Decay Identification

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

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

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)

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

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

Phonon – Ionisation

252Cf60Co

Excellent resolution in ionisation and phonon signals. Clean γ-calibration data: no event below Q = 0.7.

New Edelweiss DetectorsInterdigitized Electrode to remove “surface events”

Edelweiss / EURECA in LSM

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

Edelweiss in LSM

EURECA in LSM

Deepest site in Europe (4800 mwe)

Clean Infrastructure

24 years experience

Central location within Europe

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

LSM extension project

12m

30m

12m

A Possible Facility Layout

A Benoit

Neel Institute

Grenoble

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

~1 evt/kg/day

~3 evt/kg/year

~30 evt/ton/year

Science Results and Aims

Aim of ton-scale experiments

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