CUORE, CUORICINO: CUORE, CUORICINO: Results and Results and perspectivesperspectives
Chiara BrofferioUniversità di Milano – Bicocca and INFN, Sez. di Milano
Neutrino TelescopesVenice, 22-25 February 2005
On behalf of the CUORICINO and CUORE Collaborations
Some basic concepts on bolometersSome basic concepts on bolometers
Signal:T = E/CTime constant = C/G
LOW TEMPERATURES
Wide material choice(Phase 2 or 3?)
Very good energy resolution(no 2 background)
SOURCE = DETECTOR technique(Source mass optimization)
The detector is FULLY SENSITIVE(no dead layer)
All the energy deposited is measured(bulk and surface bkg are )
M = ~ 40.7 kg ~ 5 1025 130Te nuclei
The CUORICINO set-upThe CUORICINO set-up
CUORICINO = tower of11 modules, 4 detector (790 g) each 2 modules, 9 detector (330 g) each
I run : 29 5x5x515 3x3x6
TOTAL 130Te MASS 59 moles
II run : 40 5x5x517 3x3x6
TOTAL 130Te MASS 83 moles
This detector is completelysurrounded by active materials.
Useful for BKG origin models
330gCalibration (U + Th) sum spectrum of all the detectors
CUORICINO resultsCUORICINO results (1) (1)790g
average FWHM @ 2.6 MeV (during calibrations) 7.5 2.9 keV (790g) – 9.6 3.5 keV (330g)
The best energy resolution (790 g) @ 2615 keV is 3.9 keV
Background sum spectrum of all the big detectors in the DBD region
T1/20 (130Te) > 1.8 x 1024 y (90% c.l.)
MT = 10.8 kg y (big + small, natural)BKG = 0.18 ± 0.01 counts/ (kev kg y)
CUORICINO resultsCUORICINO results (2) (2)
mee < 0.2 – 1.1 eV
Updated to 6th Dec ’04
FWHM (790g) 7.8 keV(330g) 12.3 keV
Is CUORICINO able to scrutinize the HM experiment claim?mee = 50 meV – half life for different nuclei and models [1026 y]
T1/2 (76Ge)/T ½(130Te) 11.3 3.0 20.0 4.6 3.5 4.2
expected T ½(130Te) (units: 1024 y)
1.06 4.0 0.6 2.6 3.4 2.8 limit: > 1.8
CUORICINO and the NME modelsCUORICINO and the NME models
ElliotVogel2002
Staudt et al.
(to be compared with 28.75 events of the HM claim,with a BKG level which is 0.11 / 0.18 = 0.6 lower in HM
and with an energy resolution which is 2.5 x better in HM)
good chance to have a positive indication
BUT: cannot falsify HM if no signal is seen
CUORICINO discovery potentialCUORICINO discovery potential
141 37 251 57 44 53
Staudt et al.
Expected event number in 3 y in a 16 keV energy window (2 FWHM)
1 BKG fluctuation = (0.18 * 16 * 40.7 * 3)0.5 = 19
7.4 2.0 13 3.0 2.3 2.8
S/N ratio ()
We have identified 4 possible sources for the residual BKG in the DBD region:
Neutrons 208Tl multi-compton events and from TeO2 surface and from Cu (or other mat.) surfaces facing the crystals
Excluded since adding B-polyethilene shield had no effect
The alpha continuum extends down to the DBD region
CUORICINO background model (1)CUORICINO background model (1)
CUORICINO ~ 0.2 counts/ keV kg y
PRELIMINARY !
CUORICINO background model (2)CUORICINO background model (2)
In the COINCIDENCE spectrum only CRYSTAL SURFACE contam. contribute
In the ANTICOINCIDENCE bkg spectrum
Crystal bulk contaminations determine gaussian peaks at the Q-value of the decay
bulk crystal cont.
Surface contaminations determine peaks at the energy, with tails(shape depending on contamination depth)
surface crystal cont.
Cu surf. cont.
surface contamination level: ~ 1 ng/g vs bulk c.l. : < 1 (0.1) pg/g for Cu (TeO2)
CUORE in Gran Sasso LabsCUORE in Gran Sasso Labs
Cuoricino (Hall A)
CUORE R&D (Hall C)
CUORE location (Hall A)
CUORE detector and shieldingsCUORE detector and shieldings
CUORE is a closely packed array of 988 detectors (cylindrical option)
M = 741 kg
Each tower is a CUORICINO-like detector
19 towers with
13 planes of
4 crystals each
We intend to put heavy lead shieldings INSIDE and OUTSIDE the cryostat10 tons 60 tons
Full Montecarlo simulation on the basis of the CUORICINO and Mi DBDbackground analysis
Bulk contamination of Cu and TeO2 < 0.004 counts / kev kg y
Contamination in the cryostat shields can be made negligible by the granular structure and more Pb
Surface contamination as it is 0.074 counts / kev kg y (reduction due to decrease of Cu area and different geometry, but not enough)
We aim at reaching AT LEAST a reduction by a factor 10 in Cu surface contamination
and by a factor 4 in TeO2 surface contamination
Crystals and Copper cleaning procedure by chemical etching and surface passivation under
development
The CUORE backgroundThe CUORE background
Surface Surface Contamination Contamination RReductioneduction
New Cleaning procedure
Crystal etching
(Nitric acid)
Lapping with clean powder
(2μ SiO2)
New assembling procedure with selected clean
materials
Copper
Crystal
Radio-clean
materials
• Etching
•Electro polishing
• Passivation procedure
8-detector8-detectorss Array Array
Finally: the detector!
8-de8-detetectctorors vs. Cuoricinos vs. Cuoricino
3000 4000 5000
Hall C CUORICINO
ANTICOINCIDENCE SPECTRUM
Energy [keV]
Cou
nts
(a.u
.)
Background (3.4-4 MeV): 0.112 +/- 0.018vs 0.18 +/- 0.02
counts/keV/kg/y
We obtained a reduction of a factor 4 (average) on crystal surface contaminations: we reached the milestone of CUORE for this task.
Use a thin Ge (or TeO2) crystal to make a composite bolometer
fast high saturated pulse
“classical” pulse
“classical” pulse
Energy deposited in the TeO2 crystal (DBD-like event)
“classical” pulse
Energy deposited in the Ge crystal (degraded alpha event)
Development of surface-sensitive Development of surface-sensitive bolometersbolometers
+ =
Development of prototypes Development of prototypes
rise time distribution for Ge pulses
FASTsurface events
SLOWbulk events
Preliminary very encouraging resultsPreliminary very encouraging results
F0 = 1.5 1026 y
5 y sensitivity with pessimistic b = 0.01 counts/(keV kg y) = 10 keV
mee < 23 – 118 meV
mee < 8 – 45 meV enriched (95%) CUORE
CUORE background and sensitivityCUORE background and sensitivity
Montecarlo simulations of the background show that b ~ 0.001 counts / (keV kg y)
can be reached with the present bulk contamination of det. materials
The problem is the surface background (beta - alpha, energy-degraded):
IT MUST BE REDUCED
5 y sensitivity with optimisticb = 0.001 counts/(keV kg y) = 5 keV
mee < 11 – 57 meV
F0 = 6.5 1026 y
ConclusionsConclusions
Cuoricino experiment may confirm the HM claim soon, provided the nuclear matrix elements are reasonably favourable
A big R&D work is going on to reduce the BKG, in order to permit to CUORE experiment to investigate the inverse hierarchy region of the neutrino mass pattern
A full Montecarlo simulation for CUORE has been developed, on the basis of the CUORICINO and Mi DBD background analysis
