andrea giuliani university of insubria (como) and infn milano-bicocca italy searches for...

Andrea Giuliani

University of Insubria (Como) and INFN Milano-Bicocca

Italy

Searches for Searches for Neutrinoless Double Beta DecayNeutrinoless Double Beta Decay

Epiphany Conference Krakow

6th January 2010

OutlineOutline

Neutrino mass and Double Beta Decay

Experimental challenge and strategies

Present situation

Overview of the future projects

Some very promising experimental approaches

Prospects and conclusions

Neutrino flavor oscillationsNeutrino flavor oscillations

oscillations do occur neutrinos are massive

what we presently know from neutrino flavor oscillations

given the three mass eigenvalues M1, M2, M3 we have approximate measurements of two Mij

2

M122 ~ (9 meV)2 Solar M23

2 | ~ (50 meV)2 Atmospheric

Mij2 Mi

2 – Mj2)

e

approximate measurements and/or constraints on Ulj elementsof themixing matrix

Neutrino flavor oscillations and mass scaleNeutrino flavor oscillations and mass scale

what we do not know from neutrino flavor oscillations:

(m1)2

neutrino mass hierarchy

(m3)2 (m2)2

(m3)2

(m1)2

(m2)13

(m2)12

(m2)2

(m2)23

(m2)12

Normal hierarchy

m3>> m2~m1

Inverted hierarchy

m2~m1>>m3

(m2)2

(m3)2

(m1)2

Degeneratem1~m2~m3>>|mi-mj|

e

absolute neutrino mass scale

DIRAC or MAJORANA nature of neutrinos

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

2 Double Beta Decay

allowed by the Standard Model

already observed – 1019 y

Two decay modes are usually discussed:

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

Neutrinoless Double Beta Decay

never observed (except a discussed

claim)> 1025 y

2 0

Decay modes for Double Beta DecayDecay modes for Double Beta Decay

Neutinoless process would imply new physics beyond the Standard Model

violation of lepton number conservation

It is a very sensitive test to new physics since the phase space term is much larger than for the standard process

interest for 0-DBD lasts for more than 70 years !Goeppert-Meyer proposed the standard process in 1935Racah proposed the neutrinoless process in 1937

Double Beta Decay and neutrino physicsDouble Beta Decay and neutrino physics

Diagrams for the two processes discussed above:

Standard processtwo “simultaneous” beta decays

0-DBDa virtual neutrino is exchanged

between the two electroweak lepton vertices

DBD is a second order weak transition very low rates

Neutrino properties and 0Neutrino properties and 0-DBD-DBD

d

d

u

u

e-

e-

W-

W- e

a LH neutrino (L=1)is absorbed at this vertex

e a RH antineutrino (L=-1)is emitted at this vertex

in pre-oscillationsstandard particle physics

(massless neutrinos), the process is forbidden because

neutrino has not the correcthelicity / lepton number

to be absorbed at the second vertex

IF neutrinos are massive DIRAC particles: Helicities can be accommodated thanks to the finite mass, BUT Lepton number is rigorously conserved

0-DBD is forbidden

IF neutrinos are massive MAJORANA particles:

Helicities can be accommodated thanks to the finite mass, AND Lepton number is not relevant

0-DBD is allowed

m 0

Observation of 0-DBD

parameter containing the physics

what the nuclear theorists try to calculate

what the experimentalists try to measure

= G(Q,Z) |Mnucl|2M 2

neutrinolessDouble Beta Decay

rate

Phase space

Nuclear matrix elements Effective

Majorana mass

how 0-DBD is connected to neutrino mixing matrix and massesin case of process induced by mass mechanism

M = ||Ue1 | 2M1 + ei | Ue2 | 2M2 + ei |Ue3 | 2M3 |

< 0.2

00-DBD and neutrino physics-DBD and neutrino physics

S. Pascoli, S. T. Petcov and T. Schwetz, hep-ph/0505226

From where we start…From where we start…

76Ge claim

excluded by CUORICINO , NEMO3


……and where we want to goand where we want to go

Approach the inverted hierarchy region in a first phase (m>50 meV)

Exclude the inverted hierarchy region in a second phase (m>15 meV)

There are techniques and experiments in preparation which have the potential to reach these sensitivities


The size of the challengeThe size of the challenge

100 - 1000 counts / y ton

1 - 10 counts / y ton

0.1 - 1 counts / y ton

76Ge claim

50 meV

20 meV

OutlineOutline



Present situation




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

Q ~ 2-3 MeV for the most promising nuclidesadditional signatures: single electron energy distribution angular distribution

sum electron energy / Q

two neutrino DBDcontinuum with maximum at ~1/3 Q

neutrinoless DBDpeak enlarged only by

the detector energy resolution

Background requirementsBackground requirements

To start to explore the inverted hierarchy region

Sensitivity at the level of 1-10 counts / y ton

To cover the inverted hierarchy region

Sensitivity at the level of 0.1 -1 counts / y ton

The order of magnitude of the target bakground is ~ 1 counts / y ton

Experimental strategiesExperimental strategies

Detect and identify the daughter nuclei (indirect search)

geochemical experimentsradiochemical experiments

it is not possible to distinguish the decay channelimportant in the 70s-80s – no more pursued now

Detect the two electrons with a proper nuclear detector (direct search)

desirable features

high energy resolution

low background

large source (many nuclides under control)

event reconstruction method

a peak must be revealed over background (0-DBD)

shield cosmic rays (direct interactions and activations)

underground

very radio-pure materials238U – 232Th ~ 1010 ysignal rate > 1025 y

present more sensitive experiments: 10 - 100 kgfuture goals: ~ 1000 kg 1027 – 1028 nuclides

reject background study electron energy and angular distributions

Experimental approaches to direct searchesExperimental approaches to direct searchesTwo approaches:

e-

e-

Source Detector(calorimetric technique)

scintillation phonon-mediated detection solid-state devices gaseous detectors

very large masses are possible demonstrated: up to ~ 50 kg proposed: up to ~ 1000 kg

with proper choice of the detector, very high energy resolution

Ge-diodesbolometers

in gaseous/liquid xenon detector, indication of event topology

constraints on detector materials

in contradiction

neat reconstruction of event topology

it is difficult to get large source mass

several candidates can be studied with the same detector

e-

e-

source

detector

detector

Source Detector

scintillation gaseous TPC gaseous drift chamber magnetic field and TOF

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

sensitivity F: lifetime corresponding to the minimum detectable number of events over background at a given confidence level

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

sensitivity to M (F/Q |Mnucl|2)1/2 1 bE

MT Q1/2

1/4

|Mnucl|

F (MT / bE)1/2

energy resolutionlive time

source mass

F MT

b 0 b = 0b: specific background coefficient

[counts/(keV kg y)]

Transition energy (MeV)

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

2

3

4

5

Choice of the nuclideChoice of the nuclide

Isotopic abundance (%)

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

0

20

40

Nuclear Matrix Element

Sign of convergence!

C [

y-1]

82Se 100Mo 116Cd 130Te 136Xe 150Nd

C = |M0|2 • G0 [y-1] 2

2

102/1

em

mCT

76Ge

the real figure of merit: the higher the better

Predicted ratePredicted rate

No superisotope!

OutlineOutline



Present situation




High energy resolution (<2%)No tracking capability

Easy to reject 2 DBD background

Low energy resolution (>2%)Tracking / topology capabilityEasy to approach zero backround

(with the exception of 2 DBD component)

e-

e-

Source DetectorEasy to approach the ton scale

e-

e-

source

detector

detector

Source DetectorEasy to get tracking capability

Heidelberg-MoscowCUORICINO

NEMO-3

The Heidelberg Moscow experimentThe Heidelberg Moscow experiment

Source = detectorWell established technology of Ge diodes

Five Ge diodes for an overall mass of 10.9 kg isotopically enriched ( 86%) in 76Ge Underground operation in the Gran Sasso laboratory (Italy)

A subset of the HD collaboration (H.V. Klapdor-Kleingrothaus et al.) in 2001 announces a discussed claim

71.7 kg year – Bkg: 0.11 counts / (kg y keV) - Signal: 28.75 ± 6.87 events (Bkg:~60) Claim: 4.2 evidence T1/2 = (0.69–4.18) x1025 y (3) Best fit: T1/2 = 1.19 x1025 y (NIMA 522/PLB586) PSA analysis (Mod. Phys. Lett. A21): (2.23 + 0.44 – 0.31)x1025 y Tuebingen/Bari group (PRD79): M [eV] = 0.28 [0.17-0.45] 90%CL

Significance and T1/2 depend on Bkg model

Chkvorets, PhD dissertation Univ. HD (2008): using realistic background model peak significance reduced to 1.3, T1/2 = 2.2x1025 y

Strumia & Vissani Nucl.Phys. B726 (2005)

The Heidelberg Moscow experiment: criticismsThe Heidelberg Moscow experiment: criticisms

The claimed peak at 2039 keV

CUORICINOCUORICINO

Nuclide under study: 130Te A.I.: 34% enrichment not necessary

Source = detectorBolometric technique:young (born in ~ 1985) but now firmly established

Bolometric technique: the nuclear energy is measured as a temperatureincrease of a single crystal

T = E/C T Vthanks to a proper thermometer,

In order to get low specific heat, the temperature must be very low (5 – 10 mK)

Typical signal sizes: 0.1 mK / MeV, converted to about 1 mV / MeV

The sensitive part of the detector is a crystal of TeO2

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

Thermometer(doped Ge chip)

Sensitive mass: 41 kg

CUORICINO resultsCUORICINO results

130Te0

60Co sum peak2505 keV

~ 3 FWHM from DBD Q-value

T/2 (y) > 2.94 1024 y (90% c.l.) M < 0.20 – 0.68 eV

MT = 18 kg 130Te y

Bkg = 0.18±0.02 c/keV/kg/y

NEMO3: the structureNEMO3: the structure

Source detectorWell established technologies in particle detection:- tracking volume with Geiger cells- plastic scintillators- magnetic field

Different sources in form of foil can be used simultaneously Underground operation in the Frejus laboratory (France) Water and iron shields

The sources

1 SOURCE

2 TRACKING VOLUME

3 CALORIMETER

detector scheme

NEMO3: the resultsNEMO3: the results

NEMO 3 is a real factory → seven 2 decays observed and studied

Results with the strongest source (100Mo)F. Mauger, TAUP2009

Present results and Klapdor’s claimPresent results and Klapdor’s claim

OutlineOutline



Present situation








e-

e-


e-

e-

source

detector

detector


Experiments and techniquesExperiments and techniques

CUORE - 130TeArray of low temperature natural TeO2 calorimeters operated at 10 mKFirst step: 200 Kg (2012) – LNGS – it can take advantage from Cuoricino experienceProved energy resolution: 0.25 % FWHMGERDA - 76GeArray of enriched Ge diodes operated in liquid nitrogen or liquid argonFirst phase: 18 Kg; second phase: 40 Kg - LNGSProved energy resolution: 0.16 % FWHMMAJORANA - 76GeArray of enriched Ge diodes operated in conventional Cu cryostatsBased on 60 Kg modules; first step: 2x60 Kg modulesProved energy resolution: 0.16 % FWHMCOBRA - 116Cd competing candidate – 9 isotopesArray of 116Cd enriched CdZnTe of semiconductor detectors at room temperaturesFinal aim: 117 kg of 116CdSmall scale prototype at LNGSProved energy resolution: 1.9% FWHMLUCIFER - 82Se – 116Cd – 100Mo Array of scintillating bolometers operated at 10 mK (ZnSe or CdWO4 or ZnMoO4)First step: 20 Kg (2013) – LNGS – based on R&D performed by S. Pirro in LNGSProved energy resolution: 0.25 % FWHM

Even though these experiments do not have tracking capability, some space information and other tools help in reducing the background thanks to:GRANULARITY of the basic design- CUORE: 988 closed packed individual bolometers- COBRA: 64,000 closed packed individual detectors- MAJORANA: 57 closed packed individual diodes per modulePULSE SHAPE DISCRIMINATION- GERDA / MAJORANA can separate single / multi site eventsSEGMENTATION and PIXELLIZATIONGranularity can be achieved through electrodes segmentation R&D in progress for GERDA, MAJORANA, COBRAACTIVE SHIELDING- GERDA: Ge diodes operated in active LArSURFACE SENSITIVITY in bolometers- R&D in progress in CUORE against energy-degraded and backgroundSimultaneous LIGHT and PHONON detection in bolometers- LUCIFER Excellent / rejection power already demonstrated


rise time distribution

FASTsurface events

SLOWbulk events


e-

e-


e-

e-

source

detector

detector




Low energy resolution (>2%)Tracking / topology capability Easy to approach zero backround


CANDLES – 48CaArray of natural pure (not Eu doped) CaF2 scintillatorsProve of principle completed (CANDLES I and II)Next step (CANDLES III): under commissioning 305 kg divided in 96 crystals read by 40 PMTFurther step (CANDLES IV: requires R&D): 6.4 tons divided in 600 crystals: 6.4 Kg of 48CaFinal goal (CANDLES V): 100 ton (SNO, Kamland...)Proved energy resolution: 3.4 % FWHM (extrapolated from 9.1 % at 662 keV)The good point of this search is the high Q-value of 48Ca: 4.27 MeVout of (2.6 MeV end point), (3.3 MeV end point) and (max 2.5 MeV with quench) natural radioactivityOther background cuts come from PSD (/ different timing) and space-time correlation for Bi-Po and Bi-Tl


e-

e-


e-

e-

source

detector

detector






EXO - 136XeTPC of enriched liquid XenonEvent position and topology; in prospect, tagging of Ba single ion (DBD daughter) only 2 DBD backgroundNext step (EXO-200: funded, under commissioning): 200 kg – WIPP facility – sensitivity: 270-380 meVFurther steps: 1-10 tonProved energy resolution: 3.3 % FWHM (inproved thanks to simultaneous measurement of ionization and light)In parallel with the EXO-200 development, R&D for Ba ion grabbing and taggingBa++ e- e- final state is identified through optical spectroscopyNEXT - 136XeHigh pressure gas TPCTotal mass: 80 kgAims at energy resolution down to 1%To be installed in CANFRANC in 2013


e-

e-


e-

e-

source

detector

detector






XMASS – 136Xe Multipurpose scintillating liquid Xe detector (Dark Matter, Double Beta Decay, solar neutrinos)Three development stages: 3 Kg (prototype) 1 ton 10 tonDBD option: low background in the MeV regionSpecial development with an eliptic water tank to shield high energy gamma raysHigh light yield and collection efficiency energy resolution down to 1.4% control 2 backgroundTarget: to cover inverted hierarchy with 10 ton natural or 1 ton enriched

SNO+ – 150NdSNO detector filled with Nd-loaded liquid scintillator0.1% loading with natural Nd → 56 Kg of isotopeVery interesting and original approach. Crucial points: Nd enrichment and purity; 150Nd nuclear matrix elements


e-

e-


e-

e-

source

detector

detector




Low energy resolution (>2%)Tracking capabilityEasy to approach zero backround


SUPERNEMO - 82Se or 150NdModules with source foils, tracking (drift chamber in Geiger mode) and calorimetric (low Z scintillator) sectionsMagnetic field for charge signPossible configuration: 20 modules with 5 kg source for each module 100 Kg in Modane extensionEnergy resolution: 4 % FWHMit can take advantage of NEMO3 experienceMOON - 100Mo or 82Se or 150NdMultilayer plastic scintillators interleaved with source foils + tracking section (PL fibers or MWPC)MOON-1 prototype without tracking section (2006)MOON-2 prototype with tracking sectionProved energy resolution: 6.8 % FWHMFinal target: collect 5 y x tonDCBA - 82Se or 150NdMomentum analyzer for beta particles consisting of source foils inserted in a drift chamber with magnetic fieldPrototype: Nd2O3 foils 1.2 g of 150NdSpace resolution ~ 0.5 mm; energy resolution 11% FWHM at 1 MeV 6 % FWHM at 3 MeVFinal target: 10 modules with 84 m2 source foil for module (126 through 330 Kg total mass)

rs

PM

OutlineOutline



Present situation




CUORE = closely packed array of 988 detectors19 towers - 13 modules/tower - 4 detectors/moduleM = 741 kg

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

CUORE funding and scheduleCUORE funding and schedule

CUORE has a dedicated site in LNGS and the construction has started

The CUORE refrigerator will be commissioned in 2010

1000 crystals are funded by INFN and DoE and the delivery has started

The first CUORE tower (CUORE-0) will be assembled and operated in 2010

CUORE data taking is foreseen in 2013

CUORE sensitivityCUORE sensitivity

Background in 0 region(conservative estimate)

0.01 c/keV/kg/y

T1/20 (130Te) > 2.1 x 1026 ymββ < 44 - 73 meV

Background in 0region(optimistic estimate)

0.001 c/keV/kg/y

T1/20 (130Te) > 6 x 1026 ymββ < 25 - 43 meV

Surface background problem partially / fully

solved

Detector resolution ~ 5 keVLive time 5 years

CUORE can attack the inverted hierarchy region of the neutrino mass pattern

SuperNEMO structureSuperNEMO structure

5 - 7 kg of isotope per module Drift wire chamber operating in Geiger mode + plastic scintillators coupled to low radioactivity PMTs 20 - 22 modules for the full detector →100 – 150 kg of isotope in total modules surrounded by water shielding location: LSM (France) in one of the two new hall after the extension demonstrator operational in 2011

SuperNEMO sensitivitySuperNEMO sensitivity

ISOTOPE MASS (kg)

ENERGY RES. (FWHM)

EFFICIENCY

BACKGROUND (c / keV kg y)

2

Radon208Tl214Bi

NEMO3 SUPERNEMO

7 100-200

8% @ 3 MeV 4 % @ 3 MeV

18 % 30 %

10-3 10-4

0.7 x 10-3 0.75 x 10-4

3 mBq/m3 (20) 0.1 mBq/m3

< 20 Bq/kg 2 Bq/kg

< 300 Bq/kg 10 Bq/kg

Improvement with respect to NEMO-3

Baseline: 82SeT1/2

0 (130Te) > 1 – 1.5 x 1026 ymββ < 43 - 145 meV

Other options: 150Nd – 48Ca → advanced enrichment technologies

CUORICINO Background

-region -region130Te76Ge 100Mo116Cd

Environmental “underground” Background:

238U and 232Th contaminations

82Se

Scintillating bolometers: LUCIFERScintillating bolometers: LUCIFER

Q-value > 2.6 MeV + alpha tagging “zero” background

Scintillating bolometers: conceptsScintillating bolometers: concepts

Scintillating bolometers: the discrimination powerScintillating bolometers: the discrimination power

Scatter plot of light signals vs. heat signal

Alpha light yield < beta light yield Alpha light yield > beta light yield

Light Detector

3x3x3 CdWO4

3x3x6 CdWO4

Scintillating bolometers: test devicesScintillating bolometers: test devices

LUCIFER structure and sensitivityLUCIFER structure and sensitivity

Single module

OutlineOutline



Present situation




Future scenarios and branching points in terms of discoveryFuture scenarios and branching points in terms of discovery

100 - 500 meV

15 - 50 meV

2 - 5 meV

sensitivity to M

degenerate hierarchy 100-200 kg isotope - 5 year scaleCUORE - GERDA I / II - EXO200 - SuperNEMO - LUCIFER

inverted hierarchy - atmospheric M2 region1000 kg isotope - 10 year scalestraightforward in some cases (enriched CUORE)GERDA phase III – EXO final – CUORE in LUCIFER mode

direct hierarchy - solar M2 regionbig leap in sensitivity - new approaches required100 tons of isotopes is the typical scalediscovery if neutrino is a Majorana particleunpredictable time scale

experimental situation

if this range holds:- new strategies have to be developed- it is worthwhile to start to elaborate them now- next generation experiments are precious for the selection of the future approaches- a large investment in enrichment is mandatory

if this range holds:- SuperNEMO could marginally see it in 82Se or 150Nd- SNO++ could see it in 150Nd- GERDA phase III could see it in 76Ge- CUORE could marginally see it in 130Te, but could clearly detect it in 82Se or 116Cd if upgraded to LUCIFER-modediscovery in 3 or 4 isotopes necessary (and possible...)to confirm the observation and to improve M estimate

if this range holds (or if 76Ge claim is right):- GERDA phase I / II will see it in 76Ge- SuperNEMO may investigate the mechanism (82Se or 150Nd)- LUCIFER will see it in 82Se or 116Cd- EXO-200 will see it in 136Xe- SNO+ could see it in 150Nd- CUORE will see it in 130Te and may do multi-isotope searches simultaneously (130Te - 116Cd - 100Mo) large scale enrichment required reduction of uncertainties in NME precision measurement era for 0-DBD!

andrea giuliani university of insubria (como) and infn milano-bicocca italy searches for...

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neutrino physicsdiagrams

neutrino physicsfrom

neutrino properties

experimental sensitivity

future projects

mass scalewhat

ytwo decay modes