a cryogenic underground observatory for rare …cryogenic underground observatory for rare events...
TRANSCRIPT
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CRYOCONFERENCE 2010
9-15 September 2010
A Cryogenic Underground Observatory for Rare
Events, CUORE
Luca Pattavinaon behalf of the CUORE collaboration
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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
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e
e
ne
ne
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DBD0v featuresThe answer to all the previous questions is
neutrinoless double beta decay
• Rare event• Half-life > 1024-25 yne ne
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DBD0vEffective
neutrino massPhase space
Factor
Nuclear matrix element
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W
W
2
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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
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Calorimetric technique
Source Detector
Tracking technique
Source ≠ Detector
~ 100% efficiency
Energetic resolution
Detection volume
Topology
VV
VV
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Design of a DBD0v experiment (2)
e-e-
e-
e-detector
detector
source
detector source
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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
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Ge-NTD gold wires -> Thermal coupling
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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
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CUORE & Cuoricino (2)
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g aExcess of events @
Qββ = 2527 keV for 130Te
DBD0v signal
CUORE & Cuoricino use TeO2 crystals
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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
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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
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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
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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
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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
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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
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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
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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)
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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)
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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
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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