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CUORE: neutrinoless double beta decay with bolometers
SERGIO DI DOMIZIO
UNIVERSITю & INFN GENOVA

On behalf of the CUORE Collaboration

14th Lomonosov Conference on Elementary Particle Physics
Moscow State University, August 20th 2009


Neutrino Open Questions

13 CP violation Absolute mass scale Mass hierarchy Dirac / Majorana neutrinos
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Can be addressed by double beta decay experiments
S. Di Domizio

Lomonosov Conference on Elementary Particle Physics


Double Beta Decay
DBD is a rare process in which a nucleus changes its atomic number by 2 units

e

e-

e-

2:


A , Z A , Z 2 2 e- 2

Allowed by SM Observed for several isotopes

e

0:


A , Z A , Z 2 2 e-

ee-

Forbidden in SM Requires Majorana neutrinos L = 2 Never observed
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Underlying process

e­ W u 0 dd u e­ W



Observation of would prove with no doubt that neutrinos are Majorana particles
(Schechter and Valle, 1982)

Inference on neutrino mass requires assumptions on the decay mechanism

Simplest assumption: light Majorana exchange
Phase space
0

Nuclear matrix element
0 2



1 = 0 = G Q , Z M T 1/ 2

m

2

Effective Majorana mass

m
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=

j

U

ej

2

e

i

j

m

j


S. Di Domizio

Lomonosov Conference on Elementary Particle Physics


Light Majorana neutrino exchange
m can be expressed as a function of the mass of the lightest neutrino using the measured values of the mixing angles and of the two mass splittings

m

=

1

M0

T

0 1/ 2

GQ , Z

Phys. Rev. C 79, 044301 (2009)

Uncertainties from NME
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CUORE and CUORICINO
CUORE and CUORICINO use the bolometric technique to search for in 130Te

CUORE will be able to span the inverted mass-hierarchy region
CUORICINO is a small prototype that took data in the years 2003-2008
HALL A
Cuore & Cuoricino

Experiments located underground at the Laboratori Nazionali del Gran Sasso 3400 m w.e. rock shield against CR
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HALL C

Cuore R&D cryogenic facility
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0 experimental features
Signature:
monochromatic line at the Q-value of the decay

Sensitivity:
T1/2 corresponding to the minimum number of detectable events above background
detector mass isotopic abundance live time

S

0

Mt a bE
energy resolution
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Key features:
good energy resolution big mass low background


Background counts
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Lomonosov Conference on Elementary Particle Physics

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Bolometers
Working Principle: measure the temperature rise of the energy absorber

E T = C

requires low temperature and low heat capacity Heat bath
(~ 8 mK)

Thermal coupling
NTD Ge thermistor R ~ 100 M dR/dT ~ 0.1M/K TeO2 crystal m ~ 790 g T/E ~ 0.2 mK/MeV

Sensor

Absorber

Typical ouptut signal: 100 V per MeV of released energy
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T e O 2 B o l o m e t e r s f o r 0



130

CUORE and CUORICINO use TeO2 crystals: source detector
High isotopic abundance: 34% High Q-value: 2527 keV Easy to grow big crystals with low radioactive contaminations good mechanical properties at low temperature Low heat capacity
130



Te

Xe + 2e

-







130

Te

Q (


130

Te)

Environmental bkg spectrum

2530.3 ± 2.0 keV 2527.01 ± 0.32 keV 2527.518 ± 0.013 keV
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Lomonosov Conference on Elementary Particle Physics


CUORICINO detector
Diluition refrigerator
(Coldest point ~ 8mK)

62 TeO2 crystals Total mass: 42 Kg (11.8 Kg in
11 floors of 4 crystals Mass: 790 g Dimensions: 5x5x5 cm3 not enriched

13 0

Te)

2 floors of 9 crystals Mass: 330g Dim: 3x3x6 cm3 2 enriched in 128Te (82%) 2 enriched in 130Te (75%)

Internal (600 mK):
1cm low activity Pb
(A < 4 mBq/Kg in
210

External:

Shielding

Pb)

20cm Pb 20cm Borated Polyethylene Anti-Rn box: Nitrogen overpressure
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CUORICINO Calibration
3 days per month: 232 Th source
Sum calibration spectra 5 x 5 x 5 crystals



Avg FWHM resolution

8 keV @ 2615keV

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CUORICINO Results
60

Statistics

Co

M·t = 18 kg·y in

130

Te

0

Background

0.18 counts/keV/kg/yr

No signal found

T

0 1/2

> 2.94· 1024 y @90% C.L.


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m





< 0.21 В 0.7 eV
(NME from

Nucl. Phys. A 7 6 6 (2006) + erratum nuclth/0706.4304 )
S. Di Domizio

Lomonosov Conference on Elementary Particle Physics


CUORICINO Sensitivity
CUORICINO sensitivity is comparable to the one obtained with HPGe semiconductor detectors (Heidelberg-Moscow)

Excluded by HM

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Lomonosov Conference on Elementary Particle Physics

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CUORICINO Sensitivity
CUORICINO sensitivity is comparable to the one obtained with HPGe semiconductor detectors (Heidelberg-Moscow)

Excluded by HM

CUORICINO

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CUORE
Cryogenic Underground Observatory for Rare Events

Total mass: 741 Kg 130 Te: 203 Kg
988 TeO2 crystals 19 towers

80cm

Major efforts


M a s s inc r e a s e Background reduction

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CUORE Sensitivity
CUORICINO

CUORE



Measurement time: 5 years bkg: 0.01 counts/keV/kg/y Avg FWHM resolution: 5 keV
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T



0 1/ 2

2.110 y @ 90 C.L.


26



m

20 В 100 meV
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CUORICINO Background

60 2 14

Co

2 08

Tl degraded

Bi

Background contributions
Co from cosmogenic activation: negligible Multi-Compton from 208Tl (232Th cont. in cryostat shields): ~40%
6
0

D D

egraded from crystal surfaces: ~10% egraded from Cu holders surfaces: ~50% uon-induced background: negligible
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M

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CUORE Background
Improved cleaning procedures tested in the HALL C R&D facility




reduction by a factor 4 on Crystal surf. contaminations Reduction by a factor 2 on Cu frames surf. contaminations

Projection to CUORE
(goal: 10-2 c/keV/kg/y)

Componen t Environmen tal Apparatus Crystal bulk Crystal su rface Cu frames bulk Cu frames su rface Neu trons Mu on s
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Bkg in DBD region [10-2 c/keV/kg/y] < 0.1 < 0.1 < 0.01 < 0.3 < 0.1 ~2В4 < 0.01 < 0.01
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Lomonosov Conference on Elementary Particle Physics


CUORE Status
CUORE


Hut construction started Copper procured Cryostat Detector holders Crystal production is ongoing ~100 xtals already stored underground at LNGS Dilution refrigerator is being built





CUORE-0
The first tower of CUORE will be assembled and operated in 2010


Will be hosted in the CUORICINO cryostat Same mechanical design of the CUORE towers Test of the detector assembling procedure

CUORE data taking is foreseen to start in 2012
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Lomonosov Conference on Elementary Particle Physics

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Conclusions


Bolometers are a powerful technique for the search of Double Beta Decay CUORICINO has demonstrated the feasibility of CUORE and has set a limit on the decay time of 130Te CUORE will be able to span part of the inverted mass-hierarchy region CUORE construction is ongoing: data taking is foreseen in 2012
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