the cuore experiment: a search for neutrinoless double beta decay

The CUORE experiment: a search for

neutrinoless Double Beta Decay

Luca Gironion behalf of the CUORE collaboration

NEW TRENDS IN HIGH-ENERGY PHYSICS Alushta, Crimea

September 3-10, 2011

Luca Gironi

Outline

Alushta – 6 September 2011

• Neutrino mass

• Neutrinoless Double Beta Decay

• Experimental approach

• the bolometric technique

• Cuoricino

• the detector

• the background

• the 130Te half life limit

• CUORE

• the detector

• status

• scientific goal

• Conclusion

Neutrino oscillations and the neutrino mass• Neutrino oscillation experiments have convincingly established that neutrinos have mass

• However, the absolute mass scale and the mass hierarchy are still not known

Luca Gironi Alushta – 6 September 2011

• Great interest for non-oscillation experiments able to study absolute neutrino mass scale and its nature:

• β decay experiments

• neutrinoless Double Beta Decay (0νDBD) experiments

• cosmological observations

If neutrino has a nonzero rest mass, mass eigenstates (ν1, ν2, ν3) and weak interactions eigenstates (νe, νμ, ντ) do not necessarily have to coincide

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ilil U

3,2,1 ,, iel

eV 10 × 0.21) ±(7.59 = m 2-5212

eV 10 × 0.13) ±(2.43 = m 2-3232

The neutrino mass: cosmology, single and double beta decay


In a standard three active neutrino scenario:

cosmology

decay

0νDBD

Cosmology, single and 0νDBD measure different combinations of the neutrino mass eigenvalues, constraining the neutrino mass scale.

3

1iim

2/13

1

22

ilii Umm

2/13

1

2

i

ilii

ieUmm

αi=Majorana phases

incoherent sumreal neutrino

coherent sumvirtual neutrino

Majorana phases

simple sumpure kinematical effect

The three mass scale parameters can be plot as a function of the lightest neutrino mass.

Two bands appear in each plot, corresponding to inverted and direct hierarchy.

The two bands merge in the degenerate case (the only one presently probed).

m [

eV]

[e

V]

A. Strumia, F.VissaniarXiv:hep-ph/

0606054v3

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[eV

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Combine the informations


Primary role of neutrinoless Double Beta Decay


2νDBD22)2,(),( eZAZA eZAZA 2)2,(),(

0νDBD

Neutrinoless Double Beta Decay (0νDBD): • Requires neutrino is a massive particle

• Violates lepton number (ΔL=2), implies physics beyond Standard Model

• Allows to investigate neutrino nature: Dirac or Majorana

0νDBD and neutrino mass


• Possible for ~35 nuclei, only ~10 really interesting

• Extremely rare process (T0ν1/2 > 1024 y): 0νDBD never observed (except a

discussed claim in 76Ge)

• T0ν1/2 is the 0νββ half-life

• G0ν(Q,Z) is the 'accurately calculable' phase space factor proportional to (Q-value)5

• M0ν is the Nuclear Matrix Element (NME), which carries a theoretical uncertainty of a factor of ~2-3 depending on the nucleus

2

2

200102/1 ),(

em

mMZQGT

• <mββ> is effective double-beta neutrino mass

0νDBD: experimental approach


2νββ

0νββ

ββ summed e− energy spectrum

• Signature: Two simultaneous electrons with

summed energy Qββ, the Q-value for ββ in the

isotope under study

• Experimentalists measure the decay rate looking at a peak in the energy spectrum

• Detector Sensitivity (S): the process half-life corresponding to the maximum signal that could be detected

η: stoichiometric coefficient W: molecular weight of the active massa: isotopic abundance (i.a.)ε: detector efficiency

B

TM

W

aNS A

T : measurement live time [y]M : detector mass [kg]B : background [c/keV/kg/y]Δ : energy resolution [keV]

Experimental approachesTo reach a high sensitivity:

Experiment Isotope MethodResolution(% at Qββ)

EfficiencyBackground

(10-3 c/keV/kg/y)

Isotope Mass (kg)

CUORE 130Te bolometric 0.19 0.9 10-1 206

EXO 136Xe liquid TPC 3.3 0.7 1-0.5 160

GERDA 76Ge ionization 0.16 0.8 10-1 15-35

KamLAND-Zen 136Xe scintillation 9.5 0.8 0.5-0.1 360-1000

NEXT 136Xe gas TPC 0.7 0.3 0.2-0.06 90-1000

SNO+ 150Nd scintillation 6.5 0.5 10-1 50-500

SuperNEMO 82Se tracko-calo 4.0 0.3 0.4-0.06 7-100

Some of the under construction/funded experiments:

Other experiment: CANDLES, Majorana, COBRA, MOON, ... J.J. Gómez-Cadenas et al JCAP06(2011)007

high efficiency(source = detector)

large detector mass(100-1000kg )

very low-background(underground, shieldings, ...)

excellent energy resolution

B

TM

W

aNS A

high i.a. or enrichment possibility


Experimental approaches: the bolometric technique

• The bolometric technique offers several advantages:

• Excellent energy resolution

• Large source mass

• High efficiency

• Possibility to study all the 0νDBD isotope (cross checks)

• Among the different techniques excellent results can be obtained if source=detector

Bolometric technique: the working principle

C = heat capacityG = thermal conductance

G

Cτ

τ

t

eC

ΔEΔT(t)

Crystals, cooled to ~10 mK inside a dilution-refrigerator cryostat, have such small heat capacities that single particle interactions produce measurable rises in temperature.


130Te

High natural abundance (i.a. 130Te ~ 34%): no need for enrichment

• Q-value at ~2528 keV is above the energy range of most naturally occurring γ rays

130Te as 0νDBD candidate


TeO2 crystals

favorable characteristics of these crystals if compared with Te:

• higher Debye temperature

• rather good mechanical properties and it is possible to grow large crystals

• good intrinsic radiopurity (< 1 pg/g in 232Th and 238U)

Evolution of the bolometric technique

Cuoricino CUORECryogenic Undergound

Observatory for Rare Events

CUORE-0

2003 - 2008 2011 - 2014 2014 - 201911 kg 130Te 11 kg 130Te 206 kg 130Te

All are cryogenic bolometer experiments searching for 0νDBD decay in 130Te


Laboratori Nazionali del Gran Sasso (LNGS), Italy

NE

Underground facility

• Average depth ~ 3650 m.w.e.• Factor 106 reduction in muon flux to ~ 3×10—8 μ/(s·cm2)

LNGS underground facility

CUORE hut

Cuoricino/CUORE-0 hut


Cuoricino experiment


• CUORE predecessor

• Operated March 2003 - May 2008

• 62 TeO2 crystal bolometers:

• 44 crystals 5x5x5 cm3, (790 g)

• 18 crystals 3x3x6 cm3 (330 g)

• 14 “natural” crystals

• 2 enriched in 130Te (75%)

• 2 enriched in 128Te (82%)

• 40.7 kg TeO2 11.3 kg 130Te

Cuoricino energy spectrum

Degraded alpha energy tail

Gamma domain Alpha domain


Cuoricino single-hit background spectrum (black) and normalized 232Th calibration spectrum (red)

Anticoincidence cuts

• 0νDBD decay should produce a single-site signal 85% of the time• Excluding multi-site events reduces background by ~ 15% in the region of interest

Surface α contamination

• the main source of flat background in 3-4 MeV region due to degraded α particles

60Co

208Tl

− Cuoricino single-hit background spectrum− 232Th calibration spectrum (normalized)

• There are three main sources of background in the region of interest:

• ~40% multi-Compton events from 2615 keV γ peak of 208Tl

• ~ 50% degraded alphas from 238U and 232Th on copper surfaces

• ~ 10% degraded alphas from 238U and 232Th on crystal surfaces

214Bi

Cuoricino backgrounds


Average energy resolution (FWHM):

Background:130Te half-life limit:

Effective neutrino mass limit:

6.3±2.5 keV at Q-value in big crystals

0.169 ± 0.006 counts/keV/kg/y

> 2.8 × 1024 y (90% C.L.)

mββ < 300-710 meV

Total statistics19.75 kg·yr 130Te exposure

130Te 0νDBD

Cuoricino results

Luca Gironi Alushta – 6 September 2011uncertainty due to N.M.E.

CUORE-0


• Single CUORE-like tower (52 Te02 crystals chosen from CUORE crystals)

test of CUORE assembly and cleaning procedures

• deliver information about backgrounds

• sensitive 0νDBD experiment

• same assembly procedures as CUORE

• same cleaning procedure as CUORE

• very similar copper frames and Teflon holder

• Operated in refurbished Cuoricino cryostat

• different suspension than CUORE

• different shielding

• CUORE-0 tower construction will start Oct. 2011

• Data taking starts within 2011

CUORE


Closely packed array of 988 TeO2 crystals (5x5x5 cm3 750 g)- 19 towers

-13 planes each- 4 crystals each

• Cleaner crystals

• Higher granularity (reduction alpha background due to crystal surface thanks to anticoincidence)

• Cleaner copper and less per kg TeO2

• Cleaner assembly environment

• Copper frames less vibration-sensitive

• Better self-shielding

CUORE detector improvements

741 kg TeO2 granular calorimeter206 kg of 130Te

•Cryogen-free: better duty cycle• Detector suspension independent of refrigerator apparatus• Stringent radiopurity controls on materials and assembly

CUORE


CUORE cryostat improvements

CUORE shieldings improvements• Minimum lead thickess ≈ 36 cm (in Cuoricino ≈22 cm)

• 6 cm thick lead shield operated at ~10 mK surround the array• 30 cm of low activity lead will be used to shield from the dilution unit and from the environmental radioactivity

• Neutron shielding: 18 cm thick polyethylene + 2 cm of H3BO3 powder

CUORE


CUORE crystals

• The production started at SICCAS Jiading in 2008

• ~ 30 crystals/month

• ~ 700 crystals already at LNGS

• CUORE Crystal Validation Run – CCVR: a dedicated cryogenic setup to test crystals randomly chosen

• 7 CCVR already performed:• the bulk activity is within the limit specified in the contract with the crystals producer• improved the Cuoricino bolometric performance

• FWHM on the internal alphas from 210Po (5407 keV) = 5.2 keV on average

• lowered the energy thresholds thanks to a new trigger algorithm

- a better understanding of the background

- possibility to study Dark Matter spin independent interaction with CUORE

2008: Hut constructionCrystal production

2009–2010:Crystal productionEngineering/design/fabrication

2011:Crystal productionClean room commissioningCUORE-0

2012–2013:CUORE detector assemblyCUORE cryogenicsCUORE electronics & DAQ

2014: Data taking!

CUORE schedule


Crystal handling robot

Tower garage

Bonding tests

Gluing tests

CUORE hut

CUORE scientific goal


In 5 years of live time, with the foreseen aim of 0.01 c/keV/kg/yCUORE has a 1σ sensitivity of

yT 2602/1 106.1 meV 9541m

Conclusions

• 0νDBD plays a primary role in the study of neutrino nature, in the study absolute neutrino mass scale and has a special relevance for testing the physics beyond the standard model

• Te02 bolometers proved to be a competitive tool for the DBD search

• Cuoricino has provided the most stringent limits on 0νDBD of 130Te and showed that an experiment like CUORE is feasible

• CUORE-0 will be the first test of a CUORE-like tower from the assembly to data taking and a competitive experiment itself

• CUORE data taking is foreseen for 2014


Conclusions

Thank you for the attention!


Backup slides

130Te half-life limit (90% C.L.):

T0ν1/2>2.8 x 1024 y

Effective neutrino mass limit:

mββ < 300÷710 meV

NME bibliography:

J. Barea et al., Phys. Rev. C 79, 044301 (2009)F. Simkovic et al., Phys. Rev. C 77, 045503 (2008)O. Civitarese et al., J. Phys. Conf. Ser. 173, 012012

(2009)J. Menendez et al., Nucl. Phys. A 818, 139 (2009)

Nuclear Matrix Elements


0νDBD experiments: comparison


Sense and sensitivity of double beta decay experimentsJ.J. Gomez-Cadenas et al.Journal of Cosmology and Astroparticle PhysicsJune 2011

CUORE: Dark Matter


238U and 232Th alpha peaksdue to crystal surface contaminations

__ single hit events__ double hit events

CUORICINO coincidence analysis


1st - clean room

0th – cryostat equipment

2nd - electronics

CUORE: the hut


Crystal handling robot

Epoxy mixing/dispensing robot


CUORE gluing station, garage and working plane

Universal Working Plane

Tower garage

Bonding tests

• 4 companies to pour, work, and form low-rad copper into 6 vessels (+ flanges)• First 3 vessels (300K, 40K, 4K) are in process of being electron-beam welded• Delivery scheduled for Sep 2011• More delicate inner 3 vessels will be manufactured next year

CUORE status: the cryostat


► 10 plastic scintillators were arranged around cryostat during final 3 months of Cuoricino data taking

► Searched for correlations between muon triggers and single-site events in bolometer array

► Measured rate was consistent with zero in the 0νββ region of interest (R.O.I.), corresponding to an upper limit of:

► Cuoricino background in R.O.I. is much higher:

E. Andreotti et al. (CUORICINO Collaboration), Astropart.Phys.34:18-24 (2010) [arXiv:nucl-ex/0912.3779].

1.1 μ/hr/m2

Rμ < 0.0021 counts/keV/kg/y (95% C.L.)

RCuoricino ~ 0.2 counts/keV/kg/y

Cuoricino cosmic background study


Pulse shape and anticoincidence cuts


1. Pulse amplitude evaluation

• Pulse amplitude is the paramount observable, because it’s proportional to the amount of energy deposited

• Raw pulse is processed using so-called Optimum Filter (OF)

2. Gain stabilization

• Bolometer gain is temperature-dependent, so...• Detector response varies with natural temperature drift• Gain is “stabilized” by plotting heater pulse amplitude vs.

baseline and fitting a line to the points

3. Energy calibration

• Need to convert the stabilized pulse amplitudes to energy • Thorium sources were lowered next to detector ~ once/month

4. Global and pulse shape cuts

• Used to reject nonphysical events (e.g., electronic noise) and pileup events

5. Anticoincidence cuts

• 0νββ decay should produce a “single- site” signal 85% of the time

• Excluding multi-site events (±50 ms) reduces background by ~ 15% in the region of interest while retaining more than 99% of signal

6. Energy spectrum fit

Cuoricino analysis sequence


Phase space factor: 48Ca, 150Nd, 96Zr Nuclear matrix element not yet reliable predictions Backgrounds > 2,6 MeV 48Ca, 150Nd, 96Zr, 100Mo, 82Se, 116Cd > 3.2 MeV (radon) 48Ca, 150Nd, 96Zr Enrichment: 130Te (Natural isotopic abundance 34%) 136Xe (gaz, easy to enrich)Best techniques : Bolometers, Ge diodes: energy resolution 130Te (82Se, 116Cd), 76Ge Tracko-calo : background rejection 82Se, (48Ca, 150Nd) TPC Xe: background rejection if tagging of Ba 136Xe Large liquid scintillator: mass of isotopes 136Xe, 150Nd

What is the most favorable isotope and the best technique ?


<mn> <0.35-1.05 eV (90% CL)

T 1/2 >1.9 1025 yr (90% CL)

Eur. Phys. J., A 12 (2001) 147

0.06 cts/keV/kg/yr

Heidelberg-Moscow (2001)

~11 kg of enriched 76Ge (86%)

8.9 kg.yr without PSA4.6 kg.y with PSA

Phys. Rev. D65 (2002) 092007

IGEX (2002)~ 8.4 kg of enriched 76Ge (86%)

T 1/2 >1.57 1025 yr (90% CL)

<mn> <0.33-1.31 eV (90% CL)

Ge diode detectors


Vertex

bb events

E1+E2= 2088 keV t= 0.22 ns(vertex) = 2.1 mm

E1

E2

e-

e-

Tracko-calo detectorDrift chamber (6000 cells)Plastic scintillator + PMT (2000)10 kg of isotopesDE/E (FWHM) : 8 % @ 3 MeVLocated in Modane Underground Lab (France)

Bckg: 0.025 cts/keV/kg/yr

82Se (0,93 kg)

Multi-source detector

NEMO3


20 modules for 100 kg

Top view

Source (40 mg/cm2) 12m2

Tracking (~2-3000 Geiger cells). Calorimeter (500 channels)

5 m

1 m

Total:~ 40 000 – 60 000 geiger cells channels ~ 10 000 PMT

SuperNEMO


SuperNEMO phase I : 2011 – 2014Contruction demontrator module with 7 kg of 82SeCommissing @LSM 2013Sensitivity in 1 year: T1/2 < 5 1024 y <mn> < 0.2 – 0.6 eV

SuperNEMO phase II : 2014 – 2019100 kg of 82Se (or 150Nd,or 48Ca)T1/2 > 1026 y <mn> < 0.05 – 0.14 eV

DE/E < 4% (FWHM) @ Qbb demonstrated (< 8% @ 1 MeV)

FWHM = 7,1 %(7,6% before energy loss correction)

SuperNEMO @ LSM extension

Commissioning of wiring robot

SuperNEMO


Removal of matter

Use of liquid nitrogen or argon for active shielding

Segmented detectors in futur

Improvement of Pulse Shape Analysis

PHASE I: 17.9 kg of enriched 76Ge (from HM and IGEX)

In 1 year of data if B=10-2 cts/keV/kg/yr (check of Klapdor’s claim)

Start 2011 at Gran Sasso T1/2 > 3 1025 yr <mn> < 0.25 eV> PHASE II: 40 kg of enriched 76Ge (20 kg segmented) 2012

if B=10-3 cts/keV/kg/an T1/2 > 2 1026 yr in 3 years of data <mn> <0.1 eV>

GERDA


• Nov/Dec.’09: Liquid argon fill

• Jan ’10: Commissioning of cryogenic system

• Apr/Mai ’10: emergency drainage tests of water tank

• Apr/Mai ’10: Installation c-lock

• May ’10: 1st deployment of FE&detector mock-up

• June ‘10: Commissioning with natGe detector string

• Soon: …….

GERDA


Very pure material(Electroformed copper)

SegmentationPSD improvement

R&D phase 30-60 kg of 86% enriched 76Ge crystals

Some of the crystals segmented

T1/2 > 1. 1026 yr <mn> < 0.14 eV (could confirm or refute Klapdor’s claim)

Bckg goal ~ 1 count/ROI/t-yr (after analysis cuts)

30 kg of enriched Ge, running 3 yr. Data taking scheduled for 2011

Collaboration with Gerda for 1 ton detector

Ge diodes

Majorana


200 kg of 136Xe, no Ba ion tagging

Installation in WIPP underground labPossibility to measure bb(2n)

EXO-200 full of natural Xe - Tuning on all systems - Engineering runs - Physics mode as soon as possible

Liquid Xe TPC Ionization + scintillation DE/E (FWHM)= 3.3 % @Qbb

Possibility of Baryum ion tagging byLaser florescence (136Xe 136Ba++ + 2 e

EXO-200


EXO-200


http://arxiv.org/abs/1108.4193v1

Scintillator loaded with Nd

500 kg of 150Nd1 year<mn> = 150 meV

Test of light attenuation

Study of Nd purification (factor 1000per pass in Th and Ra)

56 kg of 150Nd (0,1 % of natural Nd) 4 yr of data <mn> ~0.08 eV

500 kg of 150Nd 4yr <mn> ~ 0.03 eV

SNO++


KamLAND-Zen


CaF2(Pure)

Liquid Scintillator(Veto Counter)

Buffer Oil

Large PMT

Pure CaF2 crystalsWave length shifter in LS

PSD to reject g and a

CANDLES III 103 cm3 × 96 crystals 305 kg Data taking in 2011 @ Kamioka Expected BG: 0.14 event/yr (30 µBq/kg) <mn> ~0.5 eV

CANDLES IV : 3 tons of CaF2 (3 mBq/kg) 6 yr <mn> ~0.1 eV

CANDLES


4x4x4 detector array = 0.42 kg CdZnTe

Installed at LNGS

Test of coincidence rejection

Measure of 113Cd

Array of 1cm3 CdZnTe detectors

Cd-113 beta decaywith half-life of about 1016 yrs

COBRA


the cuore experiment: a search for neutrinoless double beta decay

Documents

neutrino mass eigenvalues

lightest neutrino mass

coincidethe neutrino

absolute neutrino mass

neutrino nature

mass hierarchy

mass eigenstates

detector mass kgb