From Cuoricino to CUORE:

1
From Cuoricino to CUORE towards the inverted
hierarchy region
Andrea Giuliani
University of Insubria (Como) and INFN
Milano-Bicocca
On behalf of the CUORE collaboration
2
Outline of the talk

• Double Beta Decay physics and experimental
  issues

• 130Te and bolometers

• Structure of Cuoricino and present results

• From Cuoricino to CUORE

• The background model, investigation and
  solution

• Cuoricino and CUORE potential according to
  recent nuclear calculations

• Conclusions

3
Outline of the talk

• Double Beta Decay physics and experimental
  issues

• 130Te and bolometers

• Structure of Cuoricino and present results

• From Cuoricino to CUORE

• The background model, investigation and
  solution

• Cuoricino and CUORE potential according to
  recent nuclear calculations

• Conclusions

4
Decay modes for Double Beta Decay
Double Beta Decay is a very rare, second-order
weak nuclear transition which is possible for a
few tens of even-even nuclides
5
Electron sum energy spectra in DBD
The shape of the two electron sum energy spectrum
enables to distinguish among the two different
discussed decay modes
6
Experimental approaches to direct searches
Two approaches for the detection of the two
electrons
7
Outline of the talk

• Double Beta Decay physics and experimental
  issues

• 130Te and bolometers

• Structure of Cuoricino and present results

• From Cuoricino to CUORE

• The background model, investigation and
  solution

• Cuoricino and CUORE potential according to
  recent nuclear calculations

• Conclusions

8
Properties of 130Te as a DBD emitter
130Te features as a DBD candidate
large phase space, lower background (clean
window between full energy and Compton edge of
208Tl photons)
excellent feature for reasonable-cost expansion
of Double Beta Decay experiments

• high natural isotopic abundance (I.A. 33.87
  )
• high transition energy ( Q 2530 keV )
• encouraging theoretical calculations for 0n-DBD
  lifetime
• already observed with geo-chemical techniques
• ( t 1/2 incl ( 0.7 - 2.7 ) ? 1021 y)
• 2n DBD decay observed by a precursor bolometric
  experiment (MIBETA)
• and by NEMO3 at the level t 1/2 ( 5 - 7 )
  ? 1020 y

?Mbb? ? 50 meV ? t ? 2x1026 y
9
The bolometric technique for 130Te detector
concepts
10
A physical realization of bolometers for DBD
11
Outline of the talk

• Double Beta Decay physics and experimental
  issues

• 130Te and bolometers

• Structure of Cuoricino and present results

• From Cuoricino to CUORE

• The background model, investigation and
  solution

• Cuoricino and CUORE potential according to
  recent nuclear calculations

• Conclusions

12
Cuoricino and CUORE Location
Cuoricino experiment is installed in
Laboratori Nazionali del Gran Sasso L'Aquila
ITALY the mountain provides a 3500 m.w.e. shield
against cosmic rays
CUORE (hall A)
Cuoricino (hall A)
13
The CUORICINO set-up
CUORICINO tower of 13 modules,
11 modules x 4 detector (790 g) each 2
modules x 9 detector (340 g) each M 41 kg ?
5 x 1025 130Te nuclides
14
Technical results on detector performances

• Performance of CUORICINO-type detectors (5?5?5
  cm3 - 790 g)
• Detector base temperature 7 mK
• Detector operation temperature 9 mK
• Detector response 250 mV/ MeV
• FWHM resolution 3.9 keV _at_ 2.6 MeV

238U 232Th calibration spectrum
60
214Bi
Counts (/1.2 keV)
228Ac
40K
208Tl
10
2.6
1.6
0.6
Energy MeV
15
CUORICINO physics results
60Co sum peak 2505 keV 3 FWHM from DBD Q-value
MT 11.83 kg 130Te ? y
Bkg 0.180.02 c/keV/kg/y
Average FWHM resolution for 790 g detectors 7
keV
130Te 0nbb
Compilation of NME contained in Rodin et al.
Nucl. Phys. A 2006
t1/20n (y) gt 3.0 ? 1024 y (90 c.l.)
?Mbb? lt 0.20 0.98 eV
16
Outline of the talk

• Double Beta Decay physics and experimental
  issues

• 130Te and bolometers

• Structure of Cuoricino and present results

• From Cuoricino to CUORE

• The background model, investigation and
  solution

• Cuoricino and CUORE potential according to
  recent nuclear calculations

• Conclusions

17
From CUORICINO to CUORE(Cryogenic Underground
Observatory for Rare Events)
18
The CUORE collaboration
19
CUORE funding and schedule

• CUORE has a dedicated site in LNGS and the
  construction will start soon

• The CUORE refrigerator is fully funded and has
  already been ordered

• 1000 crystals are fully funded by INFN and DoE

• The first CUORE tower will be assembled in 2008
  and operated in 2009

CUORE data taking is foreseen in 2011
20
CUORE sensitivity
21
Outline of the talk

• Double Beta Decay physics and experimental
  issues

• 130Te and bolometers

• Structure of Cuoricino and present results

• From Cuoricino to CUORE

• The background model, investigation and
  solution

• Cuoricino and CUORE potential according to
  recent nuclear calculations

• Conclusions

22
The CUORE background model
The sources of the background

• Radioactive contamination in the detector
  materials (bulk and surface)
• Radioactive contamination in the set-up,
  shielding included
• Neutrons from rock radioactivity
• Muon-induced neutrons

23
The CUORE background components
Background in DBD region ( 10-3 counts/keV kg y )
Component
Environmental gamma
lt 1
Apparatus gamma
lt 1
The only limiting factor
Crystal bulk
lt 0.1
Crystal surfaces
lt 3
Close-to-det. material bulk
lt 1
Close-to-det. material surface
20 40
Neutrons
0.01
Muons
0.01
24
The Cuoricino background and the surface
radioactivity model
Gamma region
25
Reconstruction of the Cuoricino spectrum in the
region 2.5 6.5 MeV
0nDBD
26
The additional component inert material surface
contamination
In order to explain the 2.0 - 4 MeV region BKG,
one has to introduce 238U or 210Pb surface
contamination of the copper structure facing the
detectors
27
Strategies for the control of the surface
background from inert materials

• Mechanical action
• Chemical etching / electrolitical processes
• Passivation

28
Outline of the talk

• Double Beta Decay physics and experimental
  issues

• 130Te and bolometers

• Structure of Cuoricino and present results

• From Cuoricino to CUORE

• The background model, investigation and
  solution

• Cuoricino and CUORE potential according to
  recent nuclear calculations

• Conclusions

29
Cuoricino and the HM claim of evidence
Evidence of 0nDBD decay claimed by a part of the
Heidelberg-Moscow experiment (Klapdor et al.) in
the nuclide 76Ge
T1/20v (y) (0.69-4.18) ? 1025 (3s range)
Klapdor et al. Physics Letters B 586 (2004)
198-212
Best value 1.19x1025 y
Nuclear matrix element of Muto-Bender-Klapdor
mßß 0.24 0.58 eV (3s range)
30
Comparison of experimental results in a given
nuclear model
(T0n1/2)-1 G0n M0n2 ?Mbb? 2
T1/20v (Klapdor et al.)
T1/20v (130Te)
Choose a nuclear model
C. Nones, talk at. DBD06 Workshop, ILIAS-WG1,
Valencia, April 2006
31
Cuoricino and the 76Ge claim of evidence
The HM claim half life range (3s) is converted
into a corresponding range for 130Te using the
three mentioned models
Nuclear models
QRPA Tuebingen et al.
Shell model
QRPA Jyväskylä et al.
T1/2 x 1024 y for 130Te
32
CUORE and the inverted hierarchy region
?Mbb?
S. Pascoli, S.T. Petcov
Quasi-degenarate
Inverted hierarchy
Normal hierarchy
Lightest neutrino mass
33
CUORE and the inverted hierarchy region
?Mbb? band corresponding to the inverted hierarchy
34
Outline of the talk

• Double Beta Decay physics and experimental
  issues

• 130Te and bolometers

• Structure of Cuoricino and present results

• From Cuoricino to CUORE

• The background model, investigation and
  solution

• Cuoricino and CUORE potential according to
  recent nuclear calculations

• Conclusions

35
Conclusions

• Bolometers represent a well established
  technique, very competitive for
• neutrinoless DBD search
• Cuoricino is presently the most sensitive 0n DBD
  running experiment,
• with a high chance to confirm the HM claim of
  evidence if this is correct
• Cuoricino demonstrates the feasibility of a
  large scale bolometric
• detector (CUORE) with high energy resolution
  and competitive
• background
• CUORE, a next generation detector, is funded and
  will start to take
• data in 2011
• Recent results on background suppression confirm
  the capability to start
• to explore the inverted hierarchy mass region