CRYOCONFERENCE 2010

9-15 September 2010

A Cryogenic Underground Observatory for Rare

Events, CUORE

Luca Pattavinaon behalf of the CUORE collaboration

Neutrino physics

known unknown

• Neutrinos oscillate => non zero mass

• Some mixing parameters are known

• Neutrinos mass hierarchy

• Absolute mass scale• ne ne or ne = ne

_ _

2

_ _

e

e

ne

ne

_

DBD0v featuresThe answer to all the previous questions is

neutrinoless double beta decay

• Rare event• Half-life > 1024-25 yne ne

_

DBD0vEffective

neutrino massPhase space

Factor

Nuclear matrix element

3

W

W

2

Design of a DBD0v experiment (1)

i.a.: isotopic abundance

A: atomic mass number

M: source mass

T: live time

DE: FWHM in the ROI

b: bkg in the ROI

If DBD0v ∃=> Monochromatic signature

Sensitivity

4

Calorimetric technique

Source Detector

Tracking technique

Source ≠ Detector

~ 100% efficiency

Energetic resolution

Detection volume

Topology

VV

VV

|

|

|

|

Design of a DBD0v experiment (2)

e-e-

e-

e-detector

detector

source

detector source

5

Bolometric Technique

Heat bathT 10 mK

Thermal couplingG 4 nW / K = 4 pW / mK

ThermometerNTD Ge-thermistor

R 100 MW

dR/dT 0.1 MW/mK

Source/DetectorC 2 nJ/K 1 MeV / 100 mK 1mV 1MeV

E. Fiorini and T. Niinikoski, Nucl. Instrum. Methods 224, 83 (1984)

Copper-> Heat bath

Ge-NTD -> Thermometer

TeO2 -> Source/Detector

6

Ge-NTD gold wires -> Thermal coupling

CUORE & Cuoricino (1)

CUORE & Cuoricino use the bolometric technique to search for DBD0v in 130Te

CUORE will be able to span low neutrino mass region (~ meV)

Cuoricino was a small CUORE prototype, about 5 years of data taking starting in 2003

Experiments located underground @Laboratori nazionali del Gran Sasso• @ 3400 m.w.e.• Muon flux: (3.2+0.2) 10-8 m/s/cm2

• Neutron flux: 10-6-10-7 n/s/cm2

• Gamma flux >3 MeV: 0.73 g/s/cm2

R&D

CUORECuoricino

7

CUORE & Cuoricino (2)

8

g aExcess of events @

Qββ = 2527 keV for 130Te

DBD0v signal

CUORE & Cuoricino use TeO2 crystals

Cuoricino detector

Pb, Cu, B-PTFE

shieldings

Mixing Chamber

Cuoricino : 11 modules x 4 crystals (790 g) + 2 modules x 9 crystals (340 g)

= 11.6 kg of 130Te 5 x 1025 nuclei

• 2 enriched crystals @ 75% 130Te• 2 enriched crystals @ 82.3% 128Te

9

Cuoricino results

T0v1/2> 2.8*10

24 y @ 90% C.L.

mbb < 0.3 – 0.71-4 eV

Total exposure: 19.75 kg*y of 130Te

Background sources:• 208Tl multi-Compton (cryostat) : ~ 40%• U/Th surface contaminations of Cu: ~ 50%• U/Th surface contaminations of crystals: ~ 50%

60Co

10

Cuoricino results

T0v1/2> 2.8*10

24 y @ 90% C.L.

mbb < 0.3 – 0.71-4 eV

Total exposure: 19.75 kg*y of 130Te

Background sources:• 208Tl multi-Compton (cryostat) : ~ 40%• U/Th surface contaminations of Cu: ~ 50%• U/Th surface contaminations of crystals: ~ 50%

60Co

11

CUORE (1)Cryogenic Underground Observatory for Rare Events

Main concepts:

• Bigger mass: ~x20 Cuoricino

• Heavier shieldings

• Live time x5 longer than Cuoricino

• Better resolution x1.5

• Tightly packed array with a high efficiency in background rejection:

• n background x30 better• m background x20 better• crystals surface contaminations x4 better

12

CUORE (2)

19 towers * 13 modules * 4 crystals = 741 kg TeO2

80 cm

Cryogenic Underground Observatory for Rare Events

~ 1027 nuclei203 kg of 130Te (i.a. 34%)

• better surface treatment

• heavier shieldings

• custom diluition refrigerator

988 crystals

13

Cuoricino & CUORE prospects

mbb

< 0.3 – 0.7 eV

CUORE baselinebkg @DBD0v0.01 c/keV/kg/y

mbb

< 35 – 82 meV

CUORE optimisticbkg @DBD0v0.001 c/keV/kg/y

Cuoricinobkg @DBD0v0.18 c/keV/kg/y

mbb

< 20 – 47 meV

14

CUORE cryostat requirements

• Detector base temperature > 10 mK• Volume to be cooled down 1 m3

• High cooling power because ofhigh thermal load (about 2600 wires run from 10 mK to 300 K)• Anti-vibration system• Bigger shieldings• Employment of radio-pure materials• Long measurement time (10 y)

- Stable- Service-free- High duty cycle running- Cryogen-free Diluition Unit

15

CUORE cryostat construction

Suspension support

300 K SS flange (OVC)

40 K OFE copper flange

4 K SS flange (IVC)

Lead shields (1.7 t + 5.4 t) @ still temperature

Mixing chamber

Lead shield @ 50 mk (2.7 t, 30 cm thick)

CUORE detector @ 10 mK (1.5 t)

3 m

1.6 m

Pulse tube (x5)

16

Refrigerators

• Diluition Refrigerator:

• DRS-CF-2000 (Leiden Cryogenics)

• P= 5 mW (>1.5x103mW) @ 12 mK (120 mK)

PT415 Cyocooler• x5 Cryomech Pulse Tube 415

• Two Stage (300 K => 77 K; 77 K => 4 K)

• P= 1.5 W (40W) @ 4.5 K (44 K)

17

Conclusions

• Cuoricino’s performance demonstrates the feasibility of a large scale bolometric detector.

• Cuoricino set a lower limit on DBD0v half-life of T0v

1/2> 2.8*1024 y @ 90% C.L.

• CUORE is a second generation Neutrinoless Double Beta Decay experiment currently under construction.

• CUORE cryostat is the first attempt ever done of cool a mass as large as 1500 kg down to 10 mK (+ tons of shieldings to mK scale).

• CUORE data taking is forseen in 2013.18

19

20

Lead shield

Lead shield

40K

300K

4K

0.7K

70mK10mK

detectors

guide

tubes

CUORE calibration system

source locations

top view of detector array with source positions

• 12 g sources• Kevlar string from 300 K to detector• radioactive capsules crimped to the string• thermalization mechanism

Thoriated

Tungsten wire

~10m

m

Teflon

cover

Kevlar string

Source capsule