Status of CUORE and Results from CUORICINO

SERGIO DI DOMIZIOUNIVERSITÀ & INFN GENOVA

On behalf of the CUORE Collaboration

11th Seminar on Innovative Particle and Radiation DetectorsSiena, 1 October 2008

1/10/2008 2IPRD08 - SERGIO DI DOMIZIO

Outline● Double Beta Decay

– Process description– Scientific content– Experimental features

● CUORE & CUORICINO

– Double Beta Decay with Bolometers– CUORICINO: detector description and

latest results– The CUORE experiment– current status of CUORE

1/10/2008 3IPRD08 - SERGIO DI DOMIZIO

Neutrino Open Questions

➔Neutrinos have mass➔Neutrinos mix➔Almost all the Mixing matrix elements

have been measured➔ and have been measured

➔The absolute mass scale➔The sign of (hierarchy)➔Whether neutrinos are Dirac or

Majorana particles

If lepton number is not conserved, then neutrino is a neutral fermion:

can be described by a Majorana field

m ATM2

What we know What is still missingNormal hierarchy Inverted hierarchy

mSUN2 mATM

2

1/10/2008 4IPRD08 - SERGIO DI DOMIZIO

Double Beta Decay

A, Z A, Z22e−2

A, Z A, Z22e−

● Allowed by standard model● Observed for several isotopes

● Forbidden by standard model● Allowed only for Majorana neutrinos● Never observed

2:

Double beta decay is a rare process in which a nucleus changes its atomic number by 2 units

0:

1/10/2008 5IPRD08 - SERGIO DI DOMIZIO

0 Decay Time

0

=1

T 1/20

= GQ , Z ∣MNUCL∣2∣m∣

2= FN

∣m∣2

me2

m =∑mi Uei2

Nuclear matrix element(theoretical uncertainty)

phase space

experiments can measure the decay time T 1/20

effective Majorana Mass

mass of lightest neutrino [eV]

m [

eV

]

Observation of would prove that:

➔lepton number is not conserved

➔neutrinos are Majorana particles

could give informations on the absolute scale of neutrino masses

Strumia, Vissani arXiv:hep-ph/0606054

1/10/2008 6IPRD08 - SERGIO DI DOMIZIO

0 in Experiments

S0 ∝ a⋅ MtbE

energy resolution

isotopic abundancedetector mass

live time

Background counts

Signature:All the energy is shared between the 2 electrons: monochromatic line at the Q-value of the decay

Sensitivity S0decay time corresponding to the minimum number of detectable events above background

1/10/2008 7IPRD08 - SERGIO DI DOMIZIO

IPRD08 - SERGIO DI DOMIZIO1/10/2008 7

CUORE & CUORICINOCUORE and CUORICINO are bolometric

detectors for the search of decay of 130Te

CUORICINO is a small prototype of CUORE➔Completed in June 08

HALL C

Located in the undergroundGran Sasso National Labs:

3400 w.m.e. shield against cosmic rays Cuore R&D

cryogenic facility

HALL ACuore & Cuoricino

CUORE will search for decay in the inverted mass-hierarchy region

1/10/2008 8IPRD08 - SERGIO DI DOMIZIO

BolometersPrinciple: measure the temperature rise of the energy absorber

Sensor(NTD thermistor)

Absorber(dielectric & diamagnetic xtal)

Thermal bath: ~ 8 mKWeak thermal coupling

Energy release

T =EC

: requires low temperature and low heat capacity

M ~ 790 gC ~ 10-9 J/KT/E ~ 0.2 mK/MeV

Output signal: ~ 100 V / MeVR ~ 100 M (dR/dT)dR/dT ~ 100 k /K

1/10/2008 9IPRD08 - SERGIO DI DOMIZIO

TeO2 Bolometers for 0

why 130Te➔High isotopic abundance: 34%

no need for enrichment➔Q-value: ~ 2530 keV: almost

above natural background

CUORE and CUORICINO use TeO2 crystals: source detector

decay: 130Te 130Xe + 2e-

why TeO2

➔Easy to grow big crystals with low radioactive contaminations

➔Good mechanical properties➔Low heat capacity

1/10/2008 10IPRD08 - SERGIO DI DOMIZIO

CUORICINO

Internal:

Detector: a tower of 62 TeO2 crystalsMass: 42 Kg (11.8 Kg in 130Te)

Diluition refrigerator(Coldest point ~ 8mK)

2 floors made of 9 crystals:●Mass: 330g●Dim: 3x3x6 cm3

●2 enriched in 128Te (82%)●2 enriched in 130Te (75%)

11 floors made of 4 crystals●not enriched●Mass: 790g●Dimensions: 5x5x5 cm3

External:➔20cm Pb➔20cm Borated Polyethylene➔Anti-Rn box: Nitrogen

overpressure

Shielding➔1cm low activity Pb (A < 4 mBq/Kg in 210Pb)

1/10/2008 11IPRD08 - SERGIO DI DOMIZIO

CUORICINO Calibration

Average resolution: ~ 8 keV @ 2615keV

3 days every 1 month: 232Th source

Sum calibration spectra5 x 5 x 5 crystals

1/10/2008 12IPRD08 - SERGIO DI DOMIZIO

CUORICINO Results

StatisticsM·t = 15.53 kg·y in 130Te(up to August 07)

Background0.18 counts/keV/kg/yr

> 3.1· 1024 y @90% C.L.T 1 /20

< 0.20 ÷ 0.68 eV⟨m ⟩(Nuclear Matrix Element: Nucl. Phys. A 766 (2006) + erratum nucl­th/0706.4304 )

60Co

0

No signal found

Phys. Rev. C 78 (2008)

1/10/2008 13IPRD08 - SERGIO DI DOMIZIO

Total mass:741 Kg130Te: 203 Kg

CUORE

988 TeO2 crystals

19 towers

13 floors

52 crystals each

Cryogenic Underground Observatory for Rare Events

80cm

1/10/2008 14IPRD08 - SERGIO DI DOMIZIO

CUORE Sensitivity

mass of lightest neutrino [eV]

m [

eV

]T 1 / 20 2.1⋅1026 y @ 90 C.L.

m 20÷100meV

CUORE

Expected CUORE sensitivityin 5 years

Background 0.01 c/keV/Kg/y

CUORICINO

1/10/2008 15IPRD08 - SERGIO DI DOMIZIO

CUORICINO Background

Background contributions●60Co from Cu cosmogenic activation: negligible●Multi-Compton from 208Tl (232Th cont. in cryostat shields): ~40%●Degraded from crystal surfaces: ~10%

●Degraded from Cu holders surfaces: ~50%●Muon-induced background: negligible

degraded

208Tl60Co

214Bi

1/10/2008 16IPRD08 - SERGIO DI DOMIZIO

Component

< 0.1

< 0.1

Crystal bulk < 0.01

Crystal surface < 0.3

Cu frames bulk < 0.1

Cu frames surface

Neutrons < 0.01

< 0.01

Bkg in DBD region [10-2 c/keV/kg/y]

Environmental Apparatus

~ 2 ÷ 4

Muons

CUORE BackgroundTests in 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)

1/10/2008 17IPRD08 - SERGIO DI DOMIZIO

The Three Towers Test

Legnaro Cleaning: TECMTumbling

Electropolishing

Chemical etching

Magnetron sputtering

LNGS CleaningElectropolishingChemical etching

Passivation

Alternative LNGS CleaningElectropolishingChemical etching

PassivationCu frames covered with 50 m PET foil

Test the best Cu cleaning procedure➔Few months data taking, start in Nov 08➔Use CUORICINO cryostat

1/10/2008 18IPRD08 - SERGIO DI DOMIZIO

CUORE Status

● Hut construction started @LNGS

● Crystal production startedFirst batch will arrive in November 08

● Diluition refrigerator is being built

CUORE-0The first tower of CUORE will be assembled and operated in 2009:

● Test “zero-contact” assembling approach

● Same mechanical design as CUORE towers

● Will be hosted in CUORICINO cryostat

data taking is foreseen in 2012

CUORE

1/10/2008 19IPRD08 - SERGIO DI DOMIZIO

Conclusions

● Observation of decay would prove that neutrinos are Majorana particles

● 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 construction has started: data taking is foreseen in 2012