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
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