From Cuoricino to CUORE: towards the inverted hierarchy region Andrea Giuliani On behalf of the...

From Cuoricino to CUORE: From Cuoricino to CUORE: towards the inverted hierarchy regiontowards the inverted hierarchy region

Andrea Giuliani

On behalf of the CUORE collaboration

University of Insubria (Como) and INFN Milano-Bicocca

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

Outline of the talkOutline of the talk

Cuoricino and CUORE potential according to recent nuclear calculations

Conclusions

Decay modes for Double Beta DecayDecay modes for Double Beta Decay

(A,Z) (A,Z+2) + 2e-neutrinoless Double Beta Decay (0-DBD)never observed (except a discussed claim)

> 1025 y

(A,Z) (A,Z+2) + 2e- + 2e

2 Double Beta Decay allowed by the Standard Modelalready observed – 1019 y

Two decay modes are usually discussed:

Double Beta Decay is a very rare, second-order weak nuclear transitionwhich is possible for a few tens of even-even nuclides

Process would imply new physics beyond the Standard Model

violation of lepton number conservation

m 0

Observation of 0-DBD

Electron sum energy spectra in DBDElectron sum energy spectra in DBD

The shape of the two electron sum energy spectrum enables todistinguish among the two different discussed decay modes

sum electron energy / Q

two neutrino DBDcontinuum with maximum at ~1/3 Q

neutrinoless DBDpeak enlarged only by

the detector energy resolution

Experimental approaches to direct searchesExperimental approaches to direct searches

Two approaches for the detection of the two electrons:

e-

e-

Source Detector(calorimetric technique)

scintillation solid-state devices gaseous detectors cryogenic macrocalorimeters (bolometers)

No or scarce background identificationHigh efficiency

Energy resolution

e-

e-

source

detector

detector

Source Detector

scintillation gaseous TPC gaseous drift chamber with magnetic field and calorimetry

Event reconstructionLow efficiency

Low energy resolution








Conclusions

Properties of Properties of 130130Te as a DBD emitterTe as a DBD emitter

high natural isotopic abundance (I.A. = 33.87 %)

high transition energy ( Q = 2530 keV )

encouraging theoretical calculations for 0DBD lifetime

already observed with geo-chemical techniques (incl = ( 0.7 - 2.7 ) 1021 y)

2 DBD decay observed by a precursor bolometric experiment (MIBETA) and by NEMO3 at the level = ( 5 - 7 ) 1020 y

excellent feature for reasonable-cost expansion of Double Beta Decay experiments

large phase space, lower background

(clean window between full energy and Compton edge

of 208Tl photons)

M 50 meV 2x1026 y

130Te features as a DBD candidate:

The bolometric technique for The bolometric technique for 130130Te: detector conceptsTe: detector concepts

Temperature signal: T = E/C 0.1 mK for E = 1 MeV Bias: I 0.1 nA Joule power 1 pW Temperature rise 0.25 mK Voltage signal: V = I dR/dT T V = 1 mV for E = 1 MeV

Noise over signal bandwidth (a few Hz): Vrms = 0.2 V

Signal recovery time: = C/G 0.5 s

In real life signal about a factor 2 - 3 smaller

Energy resolution (FWHM): 1 keV

Heat sinkT 10 mK

Thermal couplingG 4 nW / K = 4 pW / mK

ThermometerNTD Ge-thermistor

R 100 MdR/dT 100 k

Energy absorberTeO2 crystal

C 2 nJ/K 1 MeV / 0.1 mK

Te dominates in mass the compoundExcellent mechanical and thermal properties

A physical realization of bolometers for DBDA physical realization of bolometers for DBD

Energy absorbersingle TeO2 crystal 790 g 5 x 5 x 5 cm

Thermometer(doped Ge chip)








Conclusions

Cuoricino and CUORE LocationCuoricino and CUORE Location

Cuoricino experiment is installed in

Laboratori Nazionali del Gran SassoL'Aquila – ITALY

the mountain provides a 3500 m.w.e. shield against cosmic rays

R&D final tests for CUORE (hall C)

CUORE (hall A)

Cuoricino(hall A)

CUORICINO = tower of 13 modules, 11 modules x 4 detector (790 g) each

2 modules x 9 detector (340 g) eachM = ~ 41 kg ~ 5 x 1025 130Te nuclides

The CUORICINO set-upThe CUORICINO set-up

Cold finger

Tower

Lead shield

Same cryostatand similar

structureas previous

pilot experiment

Coldest point

Technical results on detector performancesTechnical results on detector performances

2.61.60.6Energy [MeV]

Cou

nts

(/1.

2 ke

V)

10

60 238U + 232Th calibration spectrum

208Tl

214Bi

40K

228Ac

Performance of CUORICINO-type detectors (555 cm3 - 790 g):

Detector base temperature: ~ 7 mK

Detector operation temperature: ~ 9 mK Detector response: ~ 250 V/ MeV

FWHM resolution: ~ 3.9 keV @ 2.6 MeV

130Te0

60Co sum peak2505 keV

~ 3 FWHM from DBD Q-value

/20 (y) > 3.0 1024 y (90% c.l.) M < 0.20 – 0.98 eV

CUORICINO physics resultsCUORICINO physics results

MT = 11.83 kg 130Te y

Bkg = 0.18±0.02 c/keV/kg/y

Compilation of NME contained in Rodin et al. Nucl. Phys. A 2006

Average FWHM resolution for 790 g detectors: 7 keV








Conclusions

CUORE = closely packed array of 988 detectors19 towers - 13 modules/tower - 4 detectors/moduleM = 741 kg ~ 1027 130Te nuclides

Compact structure, ideal for active shielding

From CUORICINO to CUOREFrom CUORICINO to CUORE((CCryogenic ryogenic UUnderground nderground OObservatory for bservatory for RRare are EEventsvents))

Each tower is a CUORICINO-like detector

Special dilution refrigerator

The CUORE collaborationThe CUORE collaborationIT

ALY

UN

ITE

D S

TA

TE

S

CUORE funding and scheduleCUORE 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

CUORE sensitivityCUORE sensitivity

Montecarlo simulations of the background show that b ~ 0.001 counts / (keV kg y)is possible with the present bulk contamination of detector materials

The problem is the surface background (energy-degraded alpha, beta )

It must be reduced by more than a factor 10with respect to Cuoricino: work in progress!

F0 = 9.2 1025 ( T [ y ] )1/2 F0 = 2.9 1026 ( T [ y ] )1/2

5 y sensitivity (1 ) with conservative Assumption: b = 0.01 counts/(keV kg y)FWHM = 10 keV

5 y sensitivity (1 ) with aggressive assumption: b = 0.001 counts/(keV kg y)FWHM = 5 keV

M < 20 – 100 meV M < 11 – 60 meV








Conclusions

The CUORE background modelThe CUORE background model

The sources of the background

1. Radioactive contamination in the detector materials (bulk and surface)2. Radioactive contamination in the set-up, shielding included3. Neutrons from rock radioactivity4. Muon-induced neutrons

Monte Carlo simulation of the CUORE background based on:

1. CUORE baseline structure and geometry2. Gamma and alpha counting with HPGe and Si-barrier detectors 3. Cuoricino experience Cuoricino background model4. Specific measurements with dedicated detectors in test refrigerator in LNGS

Results…..

The CUORE background componentsThe CUORE background components

ComponentBackground in DBD region

( 10-3 counts/keV kg y )

Environmental gamma

Apparatus gamma

Crystal bulk

Crystal surfaces

Close-to-det. material bulk

Close-to-det. material surface

Neutrons

Muons

< 1

< 1

< 0.1

< 3

< 1

~ 20 – 40

~ 0.01

~ 0.01

The only limiting factor

The Cuoricino background The Cuoricino background and the surface radioactivity modeland the surface radioactivity model

214Bi

60Co p.u.

208Tl~ 0.11 c / keV kg y

Gamma region

Reconstruction of the Cuoricino spectrum Reconstruction of the Cuoricino spectrum in the region 2.5 – 6.5 MeV in the region 2.5 – 6.5 MeV

0DBD

Additional component required

here

The additional component: The additional component: inert material surface contamination 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

(A) Passive methods surface cleaning

(B) Active methods ( “reserve weapons” and diagnostic) events ID

Mechanical action

Chemical etching / electrolitical processes

Passivation

Strategies for the control of the surface backgroundStrategies for the control of the surface backgroundfrom inert materials from inert materials

surface sensitive bolometers

② scintillating bolometers able to separate from electrons

Claudia Nones’ talkin DM parallel section








Conclusions

Can Cuoricino scrutinize the HM claim of evidence?

T1/20v (y) = (0.69-4.18) 1025 (3σ range)

mββ= 0.24 – 0.58 eV (3σ range)

Klapdor et al.Physics Letters B 586 (2004) 198-212

Best value: 1.19x1025 y

Nuclear matrix element of Muto-Bender-Klapdor

Cuoricino and the HM claim of evidenceCuoricino and the HM claim of evidence

Evidence of 0DBD decay claimed by a part of the Heidelberg-Moscow experiment (Klapdor et al.) in the nuclide 76Ge

T1/20v

(Klapdor et al.)T1/2

0v (130Te)Choose a nuclear model

Comparison of experimental results in a given nuclear modelComparison of experimental results in a given nuclear model

2

0

0

0

0

02/11300

2/1

76

130

76

130

)()(

v

Ge

v

Te v

Ge

v

Te

vv

M

M

G

G

KlapdorTTeT

(T01/2)-1 = G0 |M0|2 M 2

QRPA Tuebingen-Bratislava -Caltech group: erratum of nucl-th/0503063

QRPA Jyväskylä group: nucl-th/0208005

Shell Model: Poves’ talk @ 4th ILIAS Annual Meeting - Chambery

For the nuclear models, consider three active schools of thoughts:

C. Nones, talk at. DBD06 Workshop, ILIAS-WG1, Valencia, April 2006

0

1

2

3

4

0 2 4 6 8 10 12T1/2 x 1024 y for 130Te

QRPA Jyväskylä et al.

Shell model

QRPA Tuebingen et al.

Cuoricino and the Cuoricino and the 7676Ge claim of evidenceGe claim of evidence

7x1024 yFinal sensitivity

3x1024 yPresent limit

The HM claim half life range (3) is converted into a corresponding range for 130Te using the three mentioned models

Nu

cle

ar

mo

de

ls

CUORE and the inverted hierarchy regionCUORE and the inverted hierarchy region

Quasi-degenarate

S. Pascoli, S.T. Petcov

Inverted hierarchy

Normal hierarchy~20 meV

~50 meV

Inverted hierarchy band

M

Lightest neutrino mass

CUORE and the inverted hierarchy regionCUORE and the inverted hierarchy region

M band corresponding to the inverted hierarchy

band of 130Te half lives

Nuclear models

0

1

2

3

4

0 5 10 15 20 25 30 35T1/2 x 1026 y for 130Te

QRPA Tuebingen et al.

Shell Model

QRPAJyväskylä et al.Nu

cle

ar

mo

de

ls

CUORE_conservative(5 y)

CUOREAggressive

(5 y)








Conclusions

ConclusionsConclusions

Bolometers represent a well established technique, very competitive for neutrinoless DBD search

Cuoricino is presently the most sensitive 0DBD 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

From Cuoricino to CUORE: towards the inverted hierarchy region Andrea Giuliani On behalf of the...

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