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Double beta decay and Majorana neutrinos

Presently an essential problem in neutrino andin astroparticle physiss

→ →<= => Majorana =>1937

Ettore Fiorini, Venice March 8, 2007

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The most sensitive way to investigate the Dirac or Majorana nature of theneutrino is neutrinoless double beta decay (DBD)This very rare process was sugested in general form by Maria Goepper Mayerjust one year after the Fermi theory of beta decay. Also Bruno Pontecorvo wasdeeply involved.

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Double Beta –Disintegration

M.Goeppert-Mayer, The John Hopkins University(Received May, 20 , 1935)

From the Fermi theory of β− disintegration the probability ofsimultameous emission of two electrons (and two neutrinos) has beencalculated. The result is that this process occurs sufficiently rarely toallow an half-life of over 1017 years for a nucleus, even if its isobar ofatomic number different by 2 were more stable by 20 times the electronmass

Double beta decay was at the beginning searched In the Double beta decay was at the beginning searched In the neutrinolessneutrinolesschannel as a powerful way to search for channel as a powerful way to search for lepton number nonlepton number nonconservationconservation. Presently it is also considered as the most powerful. Presently it is also considered as the most powerfulway to investigate the value of the way to investigate the value of the massmass of a of a MajoranaMajorana neutrino neutrino

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1. (A,Z) => (A,Z+2) + 2 e- + 2 νe¯2. (A,Z) => (A,Z+2) + 2 e- + χ ( …2,3 χ)3. (A,Z) => (A,Z+2) + 2 e-

Process 1 has been detected in ten nucleiProcess2 and 3. violate the lepton numberProcess 3, normally called neutrinoless DBD, would be revealed bythe presence of a peak in the sum of the electron energies => <mν>≠ 0

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u e -d

de -

W

u

νe

νe

2ν - ββ decay

W

0ν - ββ decay

e -

e -

d

du

u

WW

eνe

ν

Neutrinoless ββ decay

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1/τ = G(Q,Z) |Mnucl|2 <mν>2

rate of DDB-0ν Phase space Nuclear matrix elements

EffectiveMajorana neutrino mass

The rate of neutrinoless DBD strongly depends on theevaluation of the nuclear matrix elements, quite

uncertain so far

Need to search for neutrinoless DBD in various nucleiA pick could be due to some unforeseen background peak

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Possible schemes for neutrino masses

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New calculations by.S.Pascoli and S.T.Petkov

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Experimental approaches

Direct experiments

Source ≠ detectorSource = detector(calorimetric)

Geochemical experimentsi82Se = > 82Kr, 96Zr = > 96Mo (?) , 128Te = > 128Xe (non confirmed), 130Te = > 130Te

Radiochemical experiments238U = > 238Pu (non confirmed)

e-

e-

e-

e-

source

detector

detector

Source ≠ Detector

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Incidentparticle

absorber crystal

heat bath

Thermal sensor

Cryogenic detectors

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2T

VCk E !="

ΔΕ @ 5 keV ~100 mk ~ 1 mg <1 eV

~ 3 eV @ 2 MeV ~10 mk ~ 1 kg <10 eV ~

keV

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Resolution of the 5x5x5 cm3(~ 760 g ) crystals

:0.8 keV FWHM @ 46 keV1.4 keV FWHM @ 0.351 MeV2.1 keV FWHM @ 0.911 MeV2.6 keV FWHM @ 2.615 MeV3.2 keV FWHM @ 5.407 MeV

(the best α spectrometer everrealized)

Energy [keV]

Cou

nts

210Po α line

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1.1 -2.9>1.2x1024scintillator6924768.9DAMA136Xe

3 - ?>1.2x1021tracking9133675.6Irvine150Nd

.16-.82.>2x1024bolometric252933.8Cuoricino130Te

.1-4>7.7 × 1024geochem252934Bernatovitz128Te

1.7 - ?>1.7x1023scintillator8330347.5Solotvina116Cd

.7-2.8>4.6x1023tracking95-9930349.6NEMO 3100Mo

1.8-4.9>1.x1023tracking9729959.2NEMO 382Se

.441.2x1025ionization8720397.8Klapdor et al76Ge

.14 – 1.2>1.6x1025Ionization8720397.8IGEX76Ge

.12 - 1>1.9x1025ionization8720397.8Heidelberg-Moscow

76Ge

7-45>1.4x1022scintillator42710.19Elegant IV48Ca

<mν)Τ0ν (y)TechniqueEnrQββ%ExperimentNucleus

Present experimental situationPresent experimental situation

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HM collaboration subset (KDHK):HM collaboration subset (KDHK):claim of evidence of 0claim of evidence of 0νν-DBD-DBD

In December 2001, 4 authors (KDHK) of the HM collaboration announce the discovery of neutrinoless DBD

τ1/20ν (y) = (0.8 – 18.3) × 1025 y (1 × 1025 y b.v.)

〈Mββ〉 = 0.05 - 0.84 eV (95% c.l.)

54.98 kg•y 2.2 σ

2001

71.7 kg•y 4 σ

2004

skepticism in DBD community in 2001 better results in 2004

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Two new experiments NEMO III and CUORICINO

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100Mo 6.914 kg Qββ = 3034 keV

82Se 0.932 kg Qββ = 2995 keV

116Cd 405 g Qββ = 2805 keV

96Zr 9.4 g Qββ = 3350 keV

150Nd 37.0 g Qββ = 3367 keV

Cu 621 g

48Ca 7.0 g Qββ = 4272 keV

natTe 491 g

130Te 454 g Qββ = 2529 keV

ββ2ν measurement

External bkg measurement

ββ0ν search

ββββ decay isotopes in NEMO-3 detector decay isotopes in NEMO-3 detector

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0ν analysis

100Mo ⇒ τ1/20ν (y) > 4.6 × 1023 〈Mββ〉 < 0.7 – 2.8 eV (90% c.l.)

82Se ⇒ τ1/20ν (y) > 1.0 × 1023 〈Mββ〉 < 1.7 – 4.9 eV (90% c.l.)

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CUORICINO

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11 modules, 4 detector each,crystal dimension 5x5x5 cm3

crystal mass 790 g4 x 11 x 0.79 = 34.76 kg of TeO2

2 modules, 9 detector each,crystal dimension 3x3x6 cm3

crystal mass 330 g9 x 2 x 0.33 = 5.94 kg of TeO2

Search for the 2β|oν in 130Te (Q=2529 keV) and other rare events

At Hall A in the Laboratori Nazionali del Gran Sasso (LNGS)

18 crystals 3x3x6 cm3 + 44 crystals 5x5x5 cm3 = 40.7 kg ofTeO2Operation started in the beginning of 2003 => ~ 4 months

Background .18±.01 c /kev/ kg/ a

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Present CUORICINO result (new)Present CUORICINO result (new)

60Co pile-up peak

130Te DBD Q-value

anticoincidence spectrum 208Tl line

Energy [keV]

detail

DBD

MT = 5.87 (kg 130Te) x y

b = 0.18 ± 0.02 c/keV/kg/y

(Jul 2005)

8.35 kg year of 130Te

<m0ν> < .16 - .9 eV =>

τ >3 x 1024 (90 % c.l.)

Klapdor et al m0ν < .1- .9 eV

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Cosmological disfavoured region (WMAP)

Direct hierarchyΔm2

12= Δm2

sol

Inverse hierarchyΔm2

12= Δm2atm

“quasi” degeneracym1≈ m2 ≈ m3

With the same matrix elements the Cuoricino limit is 0.53 eV

Present Cuoricino region

Possible evidence(best value 0.39 eV)

H.V. Klapdor-Kleingrothaus et al., Nucl.Instrum.andMeth. ,522, 367 (2004).

Feruglio F. , Strumia A. , Vissani F. hep-ph/0201291

Arnaboldi et al., submitted to PRL, hep-ex/0501034(2005).

DBD and Neutrino Masses

27Scintillation33675.6150NdSNOLAB+Ionization28057.5115CdCOBRA

65-?Scintillation1x1026200-173022160GdGSO50-94Scintillation3x1027-4271.1948CaCARVEL29-54Scintillation3x1027.35-4271.1948CaCandles16-22Tracking1x10268033675.6150NdDCBA-213-48Tracking1.7x10273.88530349.6100MoMoon-312-31Tracking1.3x1028.556524768.9136XeEXO

54-167Tracking2102619029958.782SeSupernemo13-42Ionization1x1028.49020397.876GeGENIUS21-67Ionization4x1027.69020397.876GeMajorana29-94Ionization2x10273.859020397.876GeGERDA9-57Bolometric1.8x10273.590253334130TeCUORE

<m>TechT (year)Bc/y

% EQββ%Name

Next generation experiments

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Ionization

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COBRAIonization

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C0BRA

Use large amount of CdZnTe Semiconductor Detectors

Array of 1cm3

CdTe detectors

K. Zuber, Phys. Lett. B 519,1 (2001)

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• 0n: 1000 eventsper

• year with 1%natural

• Nd-loaded liquid• scintillator in

SNO++

Nd dissolved in SNO => tons of material;

maximum likelihood statistical test of the shape to extract0ν and 2ν components…~240 units of Δχ2 significance after only 1 year!

simulation:one year of data

by Alex Wright

Scintillation

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Scintillation

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Tracking SUPERNEMO

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Tracking

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■ conceptconcept: scale Gotthard experiment addingBa taggingBa tagging to suppress background (136Xe136Ba+2e)

■ single Ba detected by optical spectroscopy■ two options with 63% enriched Xe

►High pressure Xe TPCHigh pressure Xe TPC►LXe TPC + scintillationLXe TPC + scintillation

■ calorimetry + trackingcalorimetry + tracking■ expected bkg only by -2

►energy resolution E = 2%

Present R&DPresent R&D■ Ba+ spectroscopy in HP Xe / Ba+ extr.■ energy resolution in LXe (ion.+scint.)■ Prototype scale:► 200 kg enriched L136Xe without tagging► all EXO functionality except Ba id► operate in WIPP for ~two years■Protorype goals:►Test all technical aspects of EXO

(except Ba id)►Measure 2ν mode►Set decent limit for 0ν mode

(probe Heidelberg- Moscow)

22PP1/21/2

44DD3/23/222SS1/21/2

493 nm493 nm650 nm650 nm

metastable metastable 47s47s

LXe TPCLXe TPC

EXOEXO

Full scale experiment at WIPP orFull scale experiment at WIPP orSNOLABSNOLAB■10 t10 t (for LXe ⇒ 3 m3)

►b = 4×10-3 c/keV/ton/y►1/21/2 1.31.3××10102828 y y in 5 years►⏐⏐mm

⏐⏐ 0.013 0.013 ÷÷ 0.037 eV 0.037 eV

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CUORE CUORE expectedexpected sensitivitysensitivity

disfavoured by cosmology

11-576.5 _ 10 26510-3

19-1002.1 _ 10 26510-2

<m!> [meV]T1/2 [y]"

[keV]b (counts/keV/kg/y)

11-576.5 _ 10 26510-3

19-1002.1 _ 10 26510-2

<m!> [meV]T1/2 [y]"

[keV]b (counts/keV/kg/y)

Strumia A. and Vissani F. hep-ph/0503246

In 5 years:

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3368“5.64 " 150NdF3150NdGaO3

2528 "34 "130TeO2

2804 "7.49 "116CdWO4

3034 "9.63 "100MoPbO4

2038.7 "7.44 "76Ge

4272 keV.0187 %48CaF2

Transition energyIsotopic abundanceCompound

130Te has high transition energy and 34% isotopic abundance => enrichmentnon needed and/or very cheap. Any future extensions are possiblePerformance of CUORE, amply tested with CUORICINO

Other possible candidates for neutrinoless DBD Other possible candidates for neutrinoless DBD

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How deep should we go?

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Total Muon Flux v.s. Depth Relative to Flat Overburden(cm-2 s-1)

Depth (km.w.e) Relative to Flat Overburden

Tota

l

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Neutron Flux at Underground Sites

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eg. Study for 60 kg Majorana Module

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Neutrino oscillations ⇒ Δm2 ≠0 ⇒ <mν> finite for at leaqst one neutrino

Neutrinoless double beta decay would indicate if neutrino is a lepton violatingMajorana particle and would allow in this case to determine <mn> and thehierachy of oscillations.

This process has been indicated by an experiment (Klapdor) with a value of~0.44 eV but has not yet confirmed

Future experiments on neutrinoless double beta decay will allow to reach thesensitivity predicted by oscillations

The multidisciplinarity of searches on double beta decay involves nuclear ande subnuclear physics, astrophysics , radioactivity, material science,geochronology etc. It could help in explaining the particle-antiparticleasymmetry of the Universe

CONCLUSIONS