DOUBLE BETA DECAY

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DOUBLE BETA DECAY
Ettore Fiorini, Erice, Sept 1, 2007

• Double beta decay at the borderline between
  nuclear and subnuclear physics
• Nucleus acting as a microlaboratory to
  investigate fundamental problems in nuclear,
  subnuclear and astroparticle physics
• The neutrinoless channel since the beginning
  considered as the most poweful test of lepton
  number conservation
• after the discovery of neutrino oscillations the
  most powerful way to search for the Majorana
  nature of the neutrino and in this case to
  measure its effective mass
• Double beta decay yesterday, today and tomorrow

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Suggested in general form by Maria Goepper Mayer
just one year after the Fermi theory of beta
decay. She was interested in the nuclear point of
view
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Double Beta DisintegrationM.Goeppert-Mayer,
The John Hopkins University(Received May, 20 ,
1935)From the Fermi theory of b-
disintegration the probability of simultaneous
emission of two electrons (and two neutrinos) has
been calculated. The result is that this process
occurs sufficiently rarely to allow an half-life
of over 1017 years for a nucleus, even if its
isobar of atomic number different by 2 were more
stable by 20 times the electron mass
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The process

• (A,Z) gt (A,Z2) 2 e- 2 n -e gt detected
  in ten nuclei
• 2. (A,Z) gt (A,Z2) 2 e- c ( 2,3 c) gt
  Majoron
• 3. (A,Z) gt (A,Z2) 2 e- gt To be revealed by
  a pick gt lt mn gt? 0

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Neutrinoless bb decay
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Oscillations indicate Dm2 ? 0, but unable to
determine ltmngt
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WHERE TO SEARCH for bb DECAY?
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What are we requesting to neutrinoless DBD?
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Also essential to detemine if n is a Dirac or a
Majorana Particle
Majorana gt1937
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Nuclear matrix elements act as the value of the
effective neutrino massVarious models have been
appliedShell Model ( valid for low A nuclei,
but now ri-elaborated also for nuclei of
intermediate A) . High speed computer facilities
neededQuasiparticle Random Phase Approximation
(QRPA) ,renormalized RQRPA ( to incorporate the
Pauli principle)and pnQRPA. Quite sensitive to
the particle-particle interaction parameter g pp

• The rate of neutrinoless DBD

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Alice in the Wonderland
Amicus Plato , sed magis amica veritas Plato is
a friend, but truth even more
Only two based on exp.results ( single and two
neutrino double beta decayrecent event gt
erratum by Rodin et al
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After the erratumof Rodin et al the two QRPA
calculations based on different experimental data
( b and 2 n bb decay) tend to agree
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HM collaboration subset (KDHK) claim of
evidence of 0n-DBD
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Experimental approaches
Geochemical experimentsi82Se gt 82Kr, 96Zr gt
96Mo (?) , 128Te gt 128Xe (non confirmed), 130Te
gt 130TeRadiochemical experiments238U gt
238Pu (non confirmed)
Direct experiments
Source detector (calorimetric)
Source ? detector
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Cryogenic detectors
DE _at_ 5 keV 100 mk 1 mg
lt1 eV 3 eV _at_ 2 MeV 10 mk 1
kg lt10 eV keV
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Other possible candidates for neutrinoless DBD
130Te has high transition energy and 34 isotopic
abundance gt enrichment non needed and/or very
cheap. Any future extensions are
possible Performance of CUORE, amply tested with
CUORICINO
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Resolution of the 5x5x5 cm3 ( 760 g ) crystals
0.8 keV FWHM _at_ 46 keV 1.4 keV FWHM _at_ 0.351
MeV 2.1 keV FWHM _at_ 0.911 MeV 2.6 keV FWHM _at_
2.615 MeV 3.2 keV FWHM _at_ 5.407 MeV (the best a
spectrometer ever realized)
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Two new experiments NEMO III and CUORICINO
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116Cd 405 g Qbb 2805 keV
96Zr 9.4 g Qbb 3350 keV
150Nd 37.0 g Qbb 3367 keV
48Ca 7.0 g Qbb 4272 keV
130Te 454 g Qbb 2529 keV
100Mo 6.914 kg Qbb 3034 keV
natTe 491 g
82Se 0.932 kg Qbb 2995 keV
Cu 621 g
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CUORICINO
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• Search for the 2bon in 130Te (Q2529 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 of TeO2
• Operation started in the beginning of 2003 gt
  4 months
• Background .18.01 c /kev/ kg/ a

11 modules, 4 detector each, crystal dimension
5x5x5 cm3 crystal mass 790 g 4 x 11 x 0.79
34.76 kg of TeO2
2 modules, 9 detector each, crystal dimension
3x3x6 cm3 crystal mass 330 g 9 x 2 x 0.33 5.94
kg of TeO2
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Present CUORICINO result (new)
t gt3 x 1024 (90 c.l.)
11.8 kg year of 130Te
ltm0ngt lt .16 - .84 eV gt
Klapdor et al m0n lt .1- .9 eV
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DBD and Neutrino Masses
Present Cuoricino region
Arnaboldi et al., submitted to PRL,
hep-ex/0501034 (2005).
Possible evidence (best value 0.39 eV)
H.V. Klapdor-Kleingrothaus et al.,
Nucl.Instrum.and Meth. ,522, 367 (2004).
With the same matrix elements the
Cuoricino limit is 0.53 eV
quasi degeneracy
m1? m2 ? m3
Inverse hierarchy
?m212 ?m2atm
Direct hierarchy
?m212 ?m2sol
Cosmological disfavoured region
(WMAP)
Feruglio F. , Strumia A. , Vissani F.
hep-ph/0201291
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Next generation experiments
Bbolometric, IIonization, S Scintillation,
TTracking
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Ionization
P.Grabmayr This Conf.
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COBRA
IONIZATION
Use large amount of CdZnTe
Semiconductor Detectors
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CANDLES
L.Ogawa This Conf.
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Test ltmngt 0.150 eV
Scintillation

• 0n 1000 events per
• year with 1 natural
• Nd-loaded liquid
• scintillator in SNO

simulation one year of data
maximum likelihood statistical test of the shape
to extract 0n and 2n components240 units of
Dc2 significance after only 1 year!
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Scintillation
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Tracking SUPERNEMO
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MOON
An Option Multilayer scintillator plates and
thin MWPC tracking chambers with thin bb source
film For M0n3, E-resolution s 2.2 for N 5
ton year, ltmgt 47 32 meV for 100Mo
82Se 90 CL
Detector ?bb source Select bb sources Solar n as
well
Tracking chamber

• H. Ejiri, et al., PRL, 85, 2000.
• H. Ejiri et al., Czech. J. Phsy. 54, .

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Principle of DCBA (Drift Chamber Beta-ray
Analyzer)
150Nd?150Sm2e-
p (MeV/c) momentum, r (cm) radius, ? pitch
angle, B (kG) magnetic field, me (MeV/c2)
electron mass
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EXO
Tracking

• concept scale Gotthard experiment adding Ba
  tagging to suppress background (136Xe?136Ba??2e)
• single Ba? detected by optical spectroscopy
• two options with 63 enriched Xe
• High pressure Xe TPC
• LXe TPC scintillation
• calorimetry tracking
• expected bkg only by ??-2?
• energy resolution ?E 2

• Present RD
• 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 2n mode
• Set decent limit for 0n mode
• (probe Heidelberg- Moscow)

LXe TPC

• Full scale experiment at WIPP or SNOLAB
• 10 t (for LXe ? 3 m3)
• b 410-3 c/keV/ton/y
• ?1/2 ? 1.31028 y in 5 years
• ltm?gt ? 0.013 0.037 eV

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Array of 988 TeO2 detectors (750 g each) M 741
kg of TeO2 203 kg of 130Te
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Pb
Pb
Pb
Monica Sisti Network meeting Garching,
30.03.2007
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CUORE expected sensitivity
In 5 years
Strumia A. and Vissani F. hep-ph/0503246
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CONCLUSIONS
Neutrino oscillations ? Dm2 ?0 ? ltmngt finite for
at least one neutrino Neutrinoless double beta
decay would indicate if neutrino is a lepton
violating Majorana particle and would allow in
this case to determine ltmngt and the hierachy of
oscillations. This process has been indicated
by an experiment (Klapdor) with a value of 0.44
eV but has not been confirmed Future
experiments on neutrinoless double beta decay
will allow to reach the sensitivity predicted by
oscillations in the inverse hierarchy scheme
Better evaluations of nuclear matrix elements
both with theory and experiments are needed The
multidisciplinarity of searches on double beta
decay involves nuclear and e subnuclear
physics, astrophysics , radioactivity, material
science, geochronology etc. It could help in
explaining the particle-antiparticle asymmetry of
the Universe