Present statusPresent statusof CUORE / CUORICINOof CUORE / CUORICINO

Andrea GiulianiUniversità dell’Insubria and INFN Milano

3rd IDEA meeting, Orsay, April 14 – 15, 2005

The CUORE collaborationThe CUORE collaboration

14 institutions – 4 countries - ~ 60 physicists

The (source The (source detector) technique detector) technique

This is the most sensitive experimental technique up to nowWith high energy resolution, it can be realized in two ways:

Ge diodes + 76Ge

high energy resolution3.5 keV FWHM

reasonable candidate(Q=2039 keV)

This technique has been dominatingthe field for decades and is still one of

the most promising for the futureE. Fiorini – 60s

Bolometers + 130Te, ....

high energy resolution4 keV FWHM exceptionally

7 keV FWHM routinely

good candidate(Q=2528 keV)

other good or excellent candidates can be studied

The bolometric technique for thestudy of DBD was proposed

by E. Fiorini and T.O. Niinikoskiin 1983

sensitivity Fsensitivity F lifetime corresponding to the minimum detectable number of events over background at a given (1 ) confidence level

b: specific background coefficient [counts/(keV kg y)]

importance of the nuclide choice(but large uncertainty due to nuclear physics)

sensitivity to mee (F/Q |Mnucl|2)1/2 1 b E

MT Q1/2

1/4

|Mnucl|

F (MT / b E)1/2

energy resolutionlive time

source mass

b 0

F MT

b = 0

Experimental sensitivity to 0Experimental sensitivity to 0-DBD-DBD

130Te presents several nice features: high natural isotopic abundance (I.A. = 33.87 %) high transition energy ( Q = 2528.8 ± 1.3 keV ) encouraging theoretical calculations for 0DBD lifetime

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

large phase space, lower background

(clean window between full energy and Compton edge

of 208Tl photons)

mee 0.1 eV 1026 y

Isotopic abundance (%)

48Ca 76Ge 82Se 96Zr 100Mo 116Cd 130Te 136Xe 150Nd

0

20

40

0DBD half-life (y) for mee = 0.1 eV

(different calculations)

48Ca 76Ge 82Se 96Zr 100Mo 116Cd 130Te 136Xe 150Nd

1024

1030

1027

Comparison with other candidates:

Transition energy (MeV)

48Ca 76Ge 82Se 96Zr 100Mo 116Cd 130Te 136Xe 150Nd

2

3

4

5

C

E

23602528

2615

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

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 )

The TeOThe TeO22 bolometers history: Moore’s bolometers history: Moore’s LawLaw

CUORE

1985 1990 1995 2000 2005 2010 20150,01

0,10

1,00

10,00

100,00

1000,00

10000,00

Year

Mas

s [k

g]

Cuoricino

Mi-DBD

4 detectors array

340 g

73 g

MA

SS

(K

g)

Year

CUORE / CUORICINO in Gran Sasso LabsCUORE / CUORICINO in Gran Sasso Labs

Cuoricino (Hall A)

CUORE R&D (Hall C)

CUORE location (Hall A)

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

CUORICINO shieldingsCUORICINO shieldings

CUORICINO Tower

Cold finger

Roman lead shield

Coldest point

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 prospectsCUORICINO prospects (1) (1)

ElliotVogel2002

Staudt et al.

(to be compared with 28.75 events of the HM claim,with a BKG level which is 0.11 / 0.19 = 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 prospectsCUORICINO prospects (2) (2)

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 = (0.19 * 16 * 40.7 * 3)0.5 = 19

7.4 2.0 13 3.0 2.3 2.8

S/N ratio ()

Special dilution refrigerator

CUORE is a closely packed array of 988 detectors (cylindrical option)

M = 741 kg

Each tower is a CUORICINO-like detector

CUORECUORE

19 towers with

13 planes of

4 crystals each

F0 = 2.1 1026 y

10 y sensitivity with pessimistic b = 0.01 counts/(keV kg y) = 10 keV

mee < 0.02 – 0.1 eV

mee < 7 – 38 meV enriched 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 by a factor 40

10 y sensitivity with optimisticb = 0.001 counts/(keV kg y) = 5 keV

mee < 0.01 – 0.05 eV

F0 = 9.2 1026 y

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 !

208208Tl multi-compton in 0Tl multi-compton in 0-DBD region-DBD region

214Bi 60Co

S. E.

208Tl

To understand our background we NEED surface contaminations

CUORICINO background model (2)CUORICINO background model (2)

Surface contaminations determine peaks at the energy, with tails(shape depending on contamination depth)

Crystal bulk contaminations determine gaussian peaks at the Q-value of the decay

In the ANTICOINCIDENCE bkg spectrum

In the COINCIDENCE spectrum only CRYSTAL SURFACE contam. contribute

Fix the U and Th crystal cont. levels and depth through MC reconstruction of the COINCIDENCE spectrum in the spectral region 2.5 – 6.5 MeV

Contamination depth in crystals 1 m

problem in this region

Reconstruct the ANTICOINC. spectrum in the spectral region 2.5 – 6.5 MeV

INGREDIENTS:

210Po bulk contamination of the crystals (5.4 MeV gauss. Peak, decaying)

210Pb surface contamination of the Cu + crystal (5.3+5.4 MeV constant peak)

U + Th crystal surface contam. (fixed through the coincidence spectrum)

CUORICINO background model (3)CUORICINO background model (3)

surface contamination level: ~ 1 ng/g vs bulk c.l. : < 1 (0.1) pg/g for Cu (TeO2)

contamination depth: ~ 5 min agreement with direct measurement on Cu

CUORICINO background model (4)CUORICINO background model (4)

bulk crystal cont.

Introduce 238U or 232Th surface contamination level and depth profile due to the Cu structure facing the detectors

Dangerous events

Rejectable events(by anticoincidence)

CUORICINO background originCUORICINO background origin

TeO2 crystal TeO2 crystal

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 0.04 counts / kev kg y (reduction due to decrease of Cu area and different geometry, but not enough)

A reduction by a factor 10 in Cu surface contaminationand by a factor 4 in TeO2 surface contamination would correspond to a FULL success of CUORE

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

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

CUORE for multi-isotope searchCUORE for multi-isotope search

Calorimetric technique is powerful, but provides limited information

In case of discovery or hints for discovery, cross checks are mandatory remove doubts about unexplained lines of other origin

test nuclear models reduce systematic uncertainty on the relevant parameters, like mee

Already tested bolometricallyAs good as TeO2

CaF2, Ge, PbMoO4, CdWO4

Other compounds under test

Tests are in progress

Suitable compounds to be searched for

ConclusionsConclusions

Cuoricino experiment may confirm the HM claim soon, provided the nuclear matrix elements are reasonably favourable

An intense 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