MACHe3: Prototype of a bolometric detector

based on superfluid 3He for the search of non-baryonic Dark Matter

C. WinkelmannJ. ElbsE. CollinYu. BunkovH. GodfrinE. MoulinJ. Macias-PerezD. Santos

MACHe3: (CRTBT / LPSC)MAtrix of Cells of superfluid

Helium-3

Missing Mass and non-baryonic Dark Matter

• Flat Universe ≈ c=5.1 GeV/m3

rm≈ 1.0

• Energy density of matter in the Universe

M ≈ 1.6 GeV/m3

m≈ 0.3 ≈ 0.7

Knop et al. (2003)Spergel et al. (2003)Allen et al. (2002)

Open questions in cosmology:

Presence of large scale structures imposes

baryons ≈ 0.2 - 0.3 GeV/m3

Anomalies of galactic rotation curves

Standard Cold Dark Matter Simulation VIRGO

Vit

esse

de

rota

tion

(km

/s)

R0=8.5 kpc Honma et Sofue (1996)

0

100

200

300

0 1 2 3

MesuréMatière Visible

R/R0

Rot

atio

n ve

loci

ty k

m/s

Measured Visible Matter contribution

Non-baryonic Dark Matter: Weakly Interacting Massive Particles

Supersymmetric extension of Standard Model provides a candidate:

neutralino stable (except annihilation) relic density massive (~ 100 GeV/c2) Missing Mass neutral in charge and color Weak interaction cross section with ordinary matter

Direct detection

~

Scalar interaction

Edelweiss, CDMS,CRESST, Zeplin

Ge, Si, CaWO4, Xe

Axial interaction

DAMA/Libra, Picasso, Simple, MACHe3

NaI, F , 3He

Project of bolometric detection based on 3He

• Spin 1/2 nucleus axial interaction with neutralino

• High transparency to -rays

• Nuclear neutron capture reaction

• Limited recoil energy range: Erecoil < 6 keV

At ultra-low temperature (100 K, superfluid)

• Specific heat exp(-/kBT)

• Absolute purity

• Liquid

3He

but: expensive, technologically challenging, …

CDMS 2004

preliminary

MACHe3 Project: Potential of a bolometric detector involving10 kg / 1000 cells reduction of neutron, muon and ray background(Mayet et al., NIMA 2000).Preliminary analysis by simulation (LPSC)

Mayet et al., PLB 2002

Vibrating wire thermometry at ultra-low temperatures

The Vibrating Wire Resonator

H I0 eit

Induced voltage V

3 mm

NbTi Monofilament (4.5 m)(Photo E. Collin)

F Id

l

H

boucleV

dS

B

dt

-0.05

0

0.05

478 480 482 484 486

V (V

)

fréquence (Hz)

W(T)

Signal en phase

Signal en quadrature

V (V

)

V () A

1 2 jf freso

W

Ballistic quasiparticle gas

+pFv

-pFv

pF-pF

E

p0

1 2 3 4

Doppler shift of dispersion curves selective scattering of quasiparticles (Andreev

scattering) (Fisher et al., PRL 1989)

v v0 kBT / pF

W(T ,v) EF

exp( / kBT )

1 exp( v / v0 )

v0 / v

Non-linear damping

vrm

s (m

m/s

)

Excitation force (pN)

Bolometric detection and calibration

A

B

C

H

Stycast sealing

Copper support connected to silver sinters

Gold sheet with 57Co

Copper sheet(25 m)

Orifice for thermali-sation (200 m )

15 mm

6 mm3-cell bolometer

VWRs(4.5 et 13 m)

Response to an instantaneous heat release

0.41

0.43

0.45

0.47

0 10 20 30

Wre

t (H

z)

temps (s)

y = 0.414+m1*(m3/(m3-0.77))*...

ErrorValue

9.0417e-050.054976m1

0.00429560.057101m2

0.0122635.1739m3

NA1.5681e-05Chisq

NA0.99978R

H

A

Response time of the thermometer

w 1/W

Dynamical response of the thermometer

Wret (t) Wbase A b

b w

exp( t / b ) exp( t / w ) (t)

Wre

t (H

z)

Thermal equilibrium timeeq 1 ms

Relaxation time of the bolometer

b 1/ Sorifice 5 s

Instantaneous heat release

W0 (t) Wbase A exp( t / b ) (t)

time (s)

Bolometric calibration coefficient

Specific heat of quasiparticle gas

Vibrating Wire damping

W exp / kBT

Calibration coefficient

dW

dU

A

U

1

T

Cqp C0

Tc

T

3 / 2

exp / kBT

We neglect - Adsorbed layers- Gap reduction close to surfaces - Bosonic modes of condensate

non-exponential dependence of U on T

Non-linear dependence of W on velocity

(T,v)

+

10-9

10-8

10-7

0.1 0.12 0.14 0.16

C (

j/K

)

T (mK)

Cqp

CABS (Halperin)

1 0.4 0.15 W (Hz)

Heat capacities

5 0.01

Cadd (Greywall)

Bolometric calibration by pulsed heating

1

1.02

1.04

1.06

1.08

0 5 10 15 20

temps (s)

0

2

4

6

0 1 2

temps (s)

Energy injection by heater-VWR

linear dependence H(Upuls )Bradley et al., PRL 1995; Bäuerle et al., PRB 1998

Upuls V.Idt

Intrinsic losses in heater

Lost energy fractionWheater Wheater

int Wheaterther

Am

plit

ude (

a.u

.)W

mes(

Hz)

H

I

V

heater

thermometer

time (s)

time (s)

Detection spectra: neutrons, muons and low energy electrons

• Comparison to known energy sources

• Characterization of the detector for different types of interaction

- ionizing interaction (electron recoil):predominant for light and charged particles(rays, electrons, muons)

- non-ionizing interaction (nuclear recoil):important for massive and neutral particles(WIMP, elastic neutron scattering)

• Ionization, secondary electrons excited atomic and molecular states

- heat- ultraviolet scintillation

Heat

Ion

izati

on

/sci

nti

llati

on

Discrimination of electron recoils

Electron recoilNuclear recoil

Neutrons

nuclear neutron capture

3He n 3H p 764 keV

Elastic diffusion

m3He≈ mn fast thermalisation of neutrons

capt(n /3He) 1000

E(eV)barns

diff (n /3He) 3 barns

fast neutron thermalisation and nuclear capture : good neutron background

discrimination

0

2

4

6

8

10

0.176 0.188 0.2 0.212

Cou

ps

H (Hz)

Detection spectrum at Wbase=0.7 Hz

Cou

ps

• good agreement with description of detector

• Heat deposition :

( Bäuerle et al., Nature 1995)

• Energy deficit of 15 %

Eneutrontherm 652 20 keV

- Scintillation ?

- Topological defects ?

p=0 bar

Neutrons

70 m10 m

1 m

p

3H- Meyer, Sloan, JLTP 1998

Moderated AmBe source

Low energy electrons

Radioactive decaySource is in situ (cell B) 27

57Co 2657Fe

10 1001 E (keV)

57C

o

em

issi

on

Pile

-up

Ele

ctro

ns

pro

duce

d in

gold

sheet

136122

Moulin et al., to appear

rays

Internal conversion electrons

Auger electrons

14.413.6

7.35.50.6

21.7 27.9

260

262

264

266

0 100 200 300

W(t

) (m

Hz)

temps (s)

10 keV

• Detection of low energy electrons from 57Co • Detection threshold and resolution at keV level Expected energy range of neutralino signal reached

Wm

es(

mH

z)

time (s)

cell A (without source)cell B (with source)

Electron detection spectrum

• resolution of low energy emission spectrum of 57Co

• Comparison to 14 keV peak with bolometric calibration Energy deficit of fUV(e-,14keV)≈265%

UV Scintillation

• Energy dependence of scintillated fraction?

fUV(e->100keV)≈50%(McKinsey et al., NIMA 2002)

S/B>5Analysis LPSC, d5, B=100 mT, W0=430 mHz

Cosmic muons

• Cosmic muon flux:

Surface 150 / m2.sUnderground(Gran Sasso) 2.310-4 / m2.s

• Large cross section (100 barns) linear energy deposition (ionisation) dE/dx=1.9[g/cm3]MeV/cm

Expected energy deposition in bolometers ~ 70 keV

• Coincident detection across cells

coincidence

Wm

es(

Hz)

time (s)

Analysis and simulation

LPSC (GEANT4)

• Detection of cosmic muons: good agreement experience/simulation if

fUV(muons) ≈ 25 %

rays

• (-3He) < 1-2 barn (diffusion Compton)

<< high-Z materials (photoelectric effect)

• Difficulty of a characterization by external source (Bradley et al., PRL 1995)

• 57Co source: emission at 122 and 136 keV

no Compton edge in detection specta

cell A (without source)

cell B (with source)

Analysis LPSC

Outlook for Dark Matter search

Detector project (Mayet et al., NIMA 2002)

• 103 cells of 53 cm3

• 10 kg 3He target material• Underground laboratory

5 cm

Parallel detection of scintillation

Moulin et al., IVth. Int. Conf. Cosmo. Marseille 2004

GEANT4 Simulation (LPSC):Intrinsic rejection of neutrons and rays

Parallel ray discrimination necessary

• Ultraviolet scintillation ?

• Ionisation measurement ?

Alternative thermometry

Microfabricated VWRsSi/Al (≤10 m)(Triquenaux et al., Physica B 2000)

Thermometry by NMR

H S

Quantum coherent state of precession of magnetization

Incident particle100 K

NMR signal

3He

Homogeneous Precession Domain - NMR

4He, 30 mbar

Conclusions

• Experimental characterization of a prototype of a bolometric detector based on superfluid 3He

- Vibrating Wire thermometry- Bolometry

• Detection spectra of neutrons, low energy electrons and muons

- neutralino detection threshold reached- good understanding of the detector

• Estimation of the scintillation yield of the irradiated superfluid

discrimination of electron recoils