1. The search for neutrinoless double beta decay with Cuoricino and Cuore
Elena Guardincerri – Laboratori del Gran Sasso
On behalf of the CUORE collaboration
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

2. Discrete Conference - Elena Guardincerri
Status of v Physics
Neutrino oscillation experiments proved that neutrinos are mixed and massive
Open questions:
Absolute mass scale and the hierarchy pattern
Type of fermion: Dirac or a Majorana?
13 and values of the CP phases
Motivations for 
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

3. Neutrinoless double beta decay- d W n
2n - bb decay
Double beta decay
2nd order SM weak process
already observed with lifetimes t ~ y
Neutrinoless double beta decay
Not allowed by SM (it violates L)
Claim of observation in 76Ge: t = 2.23 x 1025 y
Mod.Phys.Lett.A21: ,2006
Neglecting the claim: t(76Ge) > 1.9 x 1025 y
Phys. Rev. D
Possible only if neutrinos are Majorana particles Schetcher, Valle Phys. Rev. D
0n - bb decay
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

4. 0 decay and effective mass
In the (standard) hypothesis that the process is mediated by the exchange of a light Majorana  the halflife for 0 is:
Effective neutrino mass
Phase space factor, ~ Q5,can be computed exactly
Nuclear matrix element, main source of uncertainty when deriving m from t
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri
From the measurement of m costraints on the mass hierarchy can be set

5. 0nbb and mass hierarchy patterns
We can express the effective neutrino mass in terms of the measured oscillation parameters and of the unknown lightest neutrino mass:
and therefore use the oscillation parameters to constraint mbb and mmin
degeneracy: m1 ~ m2 ~ m3
Next generation 0 experiments
Inverted hierarchy: m3 << m2 ~ m1
mbb in eV
best values of
oscillation parameters
1s errors for
oscillation parameters
Normal hierarchy:
m1 < m2 << m3
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri
A. Strumia, F. Vissani, arXiv.org/abs/hep-ph/

6. The bolometric technique
Principles of operation
DT = E/C
C (heat capacity) low for
low temperatures (T<<1 K) C ~ T3 (Debye)
appreciable DT
CUORE and Cuoricino bolometers are 130TeO2 x-tals
NTD Ge thermistors are used as thermometers
Very good energy resolution
See next slides
Heat sink
Cuoricino
Thermal coupling
Energy absorber
( atom x-tal)
Thermometer
(NTD thermistors in Cuoricino)
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

7. Bolometric approach: signature
Measured: sum of electrons kinetic energy
2nbb with maximum at E ≈ 1/3 Q:
uneliminable background
0nbb peak at Q = Mf – Mi
Mnucl >> me
nuclear recoil can be neglected
peak width due only to detector finite resolution
counts(a.u.)
A = A/100
sum electron energy / Q
A good energy resolution is vital!
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

8. The candidate isotopes
V. Rodin (2009) arXiv:
The decay is allowed only for some even-even nuclei for which the “standard” beta decay is forbidden by the law of conservation of energy
Nuclei with a high isotopic abundance (or easy enrichment), high M0n, and high Q value (less background from natural radioactivity, phase space factor ~ Q5) are preferable.
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

9. CUORE and Cuoricino at LNGS
3650 m.w.e. shield against cosmic rays
Cuoricino (Hall A)
Underground National Laboratory
of Gran Sasso
L'Aquila – ITALY
CUORE
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

10. The prototype: Cuoricino
5 x 5 x 5 cm3
xtals
mixing chamber
T ≈ 6 mK
Active mass:
TeO kg
130Te 11.3 kg
Cuoricino tower: 62 TeO2 crystals
roman Pb shielding (1 cm lateral)
external shields:
10 cm Pb + 10 cm low act Pb
neutron shield: B-polyethylene
nitrogen flushed anti-radon box
Faraday cage
3 x 3 x 3 cm3
xtals
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

11. Cuoricino: signal and performances
Shape:
tR ~ 10 ms
tD ~ 500 ms
Amplitude:
250 mV/MeV
~ 1 V/MeV after amplification
(ms)
232Th calibration spectrum
( 3 days of data)
Energy 2615 KeV
< DE > = (6.3 ± 2.5) keV
(for the 5 x 5 x 5 cm3 xtals)
Background: (0.153 ± 0.006) 2527 KeV
2615 keV 208Tl
single escape
double escape
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

12. Cuoricino performances: the background
a region, dominated by a peaks (internal or surface contamination)
g region, dominated by g and b events.
Highest g line: 2615 keV 208Tl (from 232Th chain)
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

13. Cuoricino results @ 90 % CL Rejection of multiple site events
Fit in the keV region
Flat bkgd keV peak + gaussian 0νββ peak
Total exposure: kg 130Te·y
Efficiency: (82.8 ± 1.1)% large xtals, (79.7 ± 1.4)% small xtals
@ 90 % CL
Various NME calculations:
Simkovic et al. PRC 77 (2008)
Civitarese et al., JoP: Conference series, 173, 2009,
Menendez et al., NPA 818 (2009) 139
Barea and Iachello, PRC 79 (2009)

14. <mbb>: Cuoricino and CUORE
Possible evidence
(best value eV)
Mod.Phys.Lett.A21: ,2006
Present Cuoricino result
degeneracy: m1 ~ m2 ~ m3
Inverse hierarchy: m3 << m2 ~ m1
mbb in eV
Normal hierarchy:
m1 < m2 << m3
B(c/keV/kg/y)
DE(keV)
t1/2(y)( 68% CL)
<mbb>(meV)
10-2 5
2.1·1026
35-82
In 5 years
Rome, December 6, 2010

15. Cuore setup and expected performances
988 TeO2 crystals (750 g each)
19 towers of 52 crystals each
741 kg TeO2
204 kg 130Te
Expected background: c/(keV kg y)
In 5 years of data taking will be sensitive to  ~2.1· y => m ~ meV
80 cm
19 times Cuoricino
NMEs from:
Simkovic et al. PRC 77 (2008)
Civitarese et al., JoP: Conference series, 173, 2009,
Menendez et al., NPA 818 (2009) 139
Barea and Iachello, PRC 79 (2009)
Rome, December 6, 2010

16. 0nbb: experimental sensitivity
The performances of 0nbb experiments can be compared introducing the detector factor of merit
For a given detector it is the process half-life measurable at 1s C.L.
Emphasized the role of the essential experimental parameters:
M = mass
T = measuring time
h = isotopical abundance
B = background level
e = detection efficiency
DE = resolution
x = bb atoms/molecule
A = compound molecular mass
NA = Avogadro number
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

17. From Cuoricino to Cuore: the challenges
M = m x 18
T = t x 5
B = b / 20
E = E / 1.5
1 σ CL
The non trivial part is achieving 0.01 c/KeV/kg/y.
CUORE is 1 ton: this means 10 c/keV/y
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

18. CUORE vs Cuoricino: improvements
Custom refrigerator + 4He-3He dilution unit
→ No cryogenic liquids for precooling
→ higher duty cycle
Mechanical suspension of the bolometers with complete decoupling from the refrigerator
→ reduction of vibration induced noise
Increased lead thickness around the detector (36 cm min vs 22 cm for Cuoricino)
→ reduced contribution from environmental radioactivity
Strict control of the radioactivity in the experimental setup
The 1 Bq 232Th contamination of Cuoricino cryostat resulted in an irreducible background ~ c/(keV⋅kg⋅y)
Improved cleaning techniques for the construction materials developed in several years of dedicated R&D
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

19. CUORE: expected background reduction
Cuoricino bkgd (0) = 0.15 c/keV/kg/y (main contributions from contaminations in the construction materials)
ϒs from cryostat internal Cu shields (bulk): ~ 30%
TeO2 and Cu surfaces: ~ 70%
From tests on crystals and copper surface cleaning:
reduction of crystal surface contamination by a factor ~ 5
clean or wrap Cu surfaces reduce the continuum background in the 3-4 MeV energy region by a factor ~ 2
Tests results (above)
Cleaner Cu shields
thicker internal Pb shield
reduced (~ ½) Cu surface area
better detector geometry resulting
in improved coincidence cuts
MC simulation
2 - 4 x10-2 c/keV/kg/y
CUORE expected bkgd (0) = 0.01 c/keV/kg/y
Still a factor to go
Most experimental efforts are now focused on the reduction of surface impurities
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri

20. Cuore status and conclusions
Cuoricino proved the feasibility of CUORE
Multiple tests performed to select the best Cu cleaning method for the frame holding the crystals
Cuore 0 will start next year
56 new Cuore crystals operated inside Cuoricino cryostat.
CUORE cleaning procedures used
CUORE hut completed
Clean room to be completed in the next month
CUORE cryostat under construction
500/988 crystals already in Gran Sasso
Data taking is scheduled to start in 2013
Rome, December 6, 2010
Discrete Conference - Elena Guardincerri