Contents

1
Contents

• Lecture 1
• General introduction
• What is measured in DBD ?
• Neutrino oscillations and DBD
• Other BSM physics and DBD
• Nuclear matrix elements
• Lecture 2
• Experimental considerations
• Current status of experiments
• Future activities
• Outlook and summary

2
Nuclear matrix elements
The dark side of double beta decay
3
Nuclear matrix elements
F. Simkovic
4
Uncertainties
F. Simkovic
5
Uncertainties
F. Simkovic
6
Reminder
2???
0???
7
Multipoles
0??? All intermediate states contribute
How to explore those???
8
Charge exchange reactions
2??? Only intermediate 1 states contribute
Supportive measurementsfrom accelerators
Currently (d,2He) and (3He,t)
9
M0? calculations
V. Rodin, A. Faessler, F. Simkovic, P. Vogel,
nucl-th/0503063
Remember Half life to neutrino mass conversion
is proportional to M2
Consequence We have to measure 3-4 isotopes to
compensate for that
Looks convincing, but not everybody agrees...
10
Summary - So far

• Neutrinoless double beta decay is the gold plated
  channel to probe the Majorana character of
  neutrinos
• It also provides information on the absolute
  neutrino mass scale
• Benchmark of 50 meV, hierarchies hard to
  disentangle, probably only way of laboratory
  experiment to go to 50 meV (ignoring claimed
  evidence)
• If observed, Schechter-Valle theorem guarantees
  Majorana neutrinos
• A lot of physics can be deduced not accessible
  to accelerators, but how to disentangle
  contributions to 0???
• However there are also major uncertainties,
  especially nuclear matrix elements
• We have achieved quite a lot, but there is still
  a lot to do

11
Can you prove that ? is Dirac?
Answer Show that neutrinos have a static
magnetic momentt
Energy in field
CPT changes sign of spin, thus Eem-Eem, bu they
must be theesame for Majorana neutrinos. Hence
12
Contents

• Lecture 1
• General introduction
• What is measured in DBD ?
• Neutrino oscillations and DBD
• Other BSM physics and DBD
• Nuclear matrix elements
• Lecture 2
• Experimental considerations
• Current status of experiments
• Future activities
• Outlook and summary

13
The search for 0???
or
14
Phase space
0nbb decay rate scales with Q5
2nbb decay rate scales with Q11
Q-value (keV)
(PS 0v)1 (yrs x eV2)
(PS 2v) 1 (yrs)
Isotope
Nat. abund. ()
 
15
Back of the envelope
T1/2 ln2 a NA M t / N?? (t??T) (
Background free)
For half-life measurements of 1024-25 yrs
1 event/yr you need 1024-25 source atoms

This is about 10 moles of isotope, implying 1 kg
Now you only can loose nat. abundance,
efficiency, background, ...
16
Spectral shapes
0??? Peak at Q-value of nuclear transition
Measured quantity Half-life
Dependencies (BG limited)
T1/2 ? a ? (Mt/?EB)1/2
link to neutrino mass
1 / T1/2 PS ME2 (m? / me)2
Sum energy spectrum of both electrons
17
Half - life estimate 0???
T1/2 ln2 a NA M t / N?? (t??T)
Signal sensitivity ? stat. precision of
background Nobs ?NBG
Background ? detector mass
T1/2 ? a ? (Mt/?EB)1/2

• a isotopical abundance

B

• M mass

• t measuring time

• ?E energy resolution

E
Q
Q?E/2
Q-?E/2

• B background (c/keV/kg/yr)

18
Signal information
(A,Z) ? (A,Z2) 2 e-
Signal One new isotope (ionised), two electrons
(fixed total energy)
Single electron energies
Angle between electrons
Sum energy of both electrons
Daughter ion (A,Z2)
Gamma rays (eg. four 511 keV photons in ??)
19
The dominant problem - Background
How to measure half-lives beyond 1020 years???
The first thing you need is a mountain, mine,...

• The usual suspects (U, Th nat. decay chains)

• Alphas, Betas, Gammas

• Cosmogenics

• thermal neutrons

• High energy neutrons from muon interactions

• 2???

20
Contents

• Lecture 1
• General introduction
• What is measured in DBD ?
• Neutrino oscillations and DBD
• Other BSM physics and DBD
• Nuclear matrix elements
• Lecture 2
• Experimental considerations
• Current status of experiments
• Future activities
• Outlook and summary

21
Geochemical approach
Major advantage Experiment is running since a
billion years
Signal Isotopical anomaly
T age of ore
Practically search has been possible due to the
high sensitivity ofnoble gas mass spectrometry.
Thus daughter should be noble gas.
? 82Se, 128,130Te
DisadvantageYou cannot discriminate2??? from
0???
T. Kirsten et al, PRL 20 (1968)
22
Experimental techniques
Source detector
Source ? detector
Time projection chambers (TPC)
Semiconductors
NEMO-3, SuperNEMO,DCBA, EXO
Heidelberg-Moscow, IGEX, COBRA, GERDA, MAJORANA
Cryogenic bolometers
CUORICINO, CUORE
Scintillators
SNO, CANDLES, MOON,GSO, XMASS
23
Heidelberg -Moscow

• Five Ge diodes (overall mass 10.9 kg)
• isotopically enriched ( 86) in 76Ge
• Lead box and nitrogen flushing of the detectors
• Digital Pulse Shape Analysis Peak at 2039 keV

24
Spectrum
0? peak region
25
Latest HD-Moscow results
Statistical significance 54.98 kg x yr
Including pulse shape analysis 35.5 kg x yr
(installed Nov. 95, only 4 detectors)
SSE
T1/2 gt 1.9 x 1025 yr (90 CL)
m lt 0.35 eV
26
Evidence for 0???-decay?- References
Latest Heidelberg-Moscow results
H.V. Klapdor-Kleingrothaus et al., Eur. Phys. J.
A 12,147 (2001)
Evidence
H.V. Klapdor-Kleingrothaus et al., Mod. Phys.
Lett. A 16,2409 (2001)
Critical comments
F. Feruglio et al., hep-ph/0201291
C.A. Aalseth et al., hep-ex/0202018
Reply
H.V. Klapdor-Kleingrothaus, hep-ph/0205228
H.L. Harney, hep-ph/0205293
New evidence
H.V. Klapdor-Kleingrothaus et al., Phys. Lett. B
586,198 (2004)
27
Heidelberg -Moscow
more statistics Recalibration
T1/2 0.6 - 8.4 x 1025 yr
m 0.17 - 0.63 eV
Subgroup of collaboration
H.V. Klapdor-Kleingrothaus et al, Phys. Lett. B
586, 198 (2004)
28
The peak...
1.) Is there a peak?
Statistical treatment (Bayesian)
2.) If it is real, is it something specific to Ge?
56Co produced by cosmic rays (2034 keV photon 6
keV X-ray)
76Ge(n,??)77Ge (2038 keV photon)
Some unknown line
Inelastic neutron scattering (n,n?) on lead
Other suggestions, can be combination of all
Note We are talking about 1 event/year
The easiest person to fool is yourself (R.
Feynman)
29
? Check with a different isotope
Uncertainties in nuclear matrix elements, example
116Cd
ltm?gt0.4eV
V. Rodin et al., nucl-th/0503063, Nucl. Phys. A
2006
30
CUORICINO-CUORE - Principle
Thermal coupling
example 750 g of TeO2 _at_ 10 mKC T 3 (Debye) ?
C 210-9 J/K1 MeV g-ray ? DT 80 mK ? DU
10 eV
31
CUORICINO - Spectrum
32
CUORICINO - Results
about 40 kg running
208Tl
60Co sum
130Te DBD
T1/2 gt 2.4 x 1024 yrs (90 CL) m lt 0.2-1.1 eV
33
CUORICINO-CUORE
19 towers
13x4 crystals/tower
Future CUORE 760 kg TeO2 approved
34
NEMO-3
Only approach with source different from detector
35
bb decay isotopes in NEMO-3 detector
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
External bkg measurement
100Mo 6.914 kg Qbb 3034 keV
82Se 0.932 kg Qbb 2995 keV
natTe 491 g
Cu 621 g
36
NEMO-III - Event
Typical 2??? event of 100Mo
37
100Mo results
7.37 kg.y
(Data Feb. 2003 Dec. 2004)
Angular Distribution
Sum Energy Spectrum
219 000 events 6914 g 389 days S/B 40
219 000 events 6914 g 389 days S/B 40
NEMO-3
NEMO-3
100Mo
100Mo
E1 E2 (keV)
Cos(?)
2???
T1/2 7.11 0.02 (stat) 0.54 (syst) ? 1018 y
0???
T1/2 gt 5.8 x 1023 yrs (90 CL)
m? lt 0.6 - 2.8 eV
Idea SuperNEMO (100 kg)
R. Arnold et al, PRL 95 (2005)
38
SuperNEMO
Idea Use 100 kg enriched 82Se
39
COBRA
Use large amount of CdZnTe
Semiconductor Detectors
Array of 1cm3 CdTe detectors
K. Zuber, Phys. Lett. B 519,1 (2001)
40
Isotopes
nat. ab. ()
Q (keV)
Decay mode
41
Advantages

• Source detector

• Semiconductor (Good energy resolution, clean)

• Room temperature (safety)

• Modular design (Coincidences)

• Two isotopes at once

Industrial development of CdTe detectors

• 116Cd above 2.614 MeV

• Tracking (Solid state TPC)

42
2??? - decay
2??? is ultimate, irreducible background
Energy resolution extremely important check
whether people use FWHM or ? (there is a factor
2.35 difference)
Fraction of 2??? in 0??? peak
S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci.
2002
Signal/Background
43
The first layer
4x4x4 detector array 0.42 kg CdZnTe
semiconductors
Installed at LNGS about three month ago
44
The solid state TPC
Energy resolution
Tracking

• Massive background
• Reduction (Particle-ID)
• Positive signal information

Pixellated CdZnTe detectors
45
Pixellisation - I

• Particle ID possible, 200?m pixels (example
  simulations)
• eg. Could achieve nearly 100 identification of
  214Bi events (214Bi ? 214Po ? 210Pb)
• .

? 1 pixel, ? and ?? several connected pixel, ?
some disconnected p.
3 MeV ?
0???
?
15?m
1-1.5mm
7.7MeV ? life-time 164.3?s
Beta withendpoint 3.3MeV
46
Pixellated detectors
Solid state TPC
3D - Pixelisation
47
Nobody said it was going to be easy, and nobody
was right
George W. Bush
48
Contents

• Lecture 1
• General introduction
• What is measured in DBD ?
• Neutrino oscillations and DBD
• Other BSM physics and DBD
• Nuclear matrix elements
• Lecture 2
• Experimental considerations
• Current status of experiments
• Future activities
• Outlook and summary

49
Back of the envelope
T1/2 ln2 a NA M t / N?? (t??T) (
Background free)
50 meV implies half-life measurements of 1026-27
yrs
1 event/yr you need 1026-27 source atoms

This is about 1000 moles of isotope, implying 100
kg
Now you only can loose nat. abundance,
efficiency, background, ...
50
Future projects, ideas
Status 2006
small scale ones will expand, very likely not a
complete list...
51
Future - Ge approaches
MAJORANA
500 kg of enrichedGe detectors
GERDA
Naked enriched Ge-crystals inLAr with lead shield
Segmentation and pulse shape discrimination
20 kg enriched Ge-detectorsat hand (former HD-MO
and IGEX), 35 kg enriched bought
MERGE
52
EXO
New feature
Tracking and scintillation
136Xe ? 136Ba e- e- final state can be
identified using optical spectroscopy (M.Moe
PRC44 (1991) 931)
200 kg enriched Xe prototype under construction
at WIPP
53
Summary
Double beta decay is the gold plated channel to
probethe fundamental character of neutrinos
Taking current evidences from oscillation data it
islikely to be the only way to fix the absolute
neutrino mass
To go below 50 meV requires hundreds of kilograms
ofenriched material
However, there is a hotly discussed evidence by
the Heidelberg group, which would imply almost
degenerate neutrinos
To account for matrix element uncertainties and
todisentangle the physics mechanism we need at
least 3(4) isotopes measured
A lot to do
54
Hope....
55
Particle particle coupling gpp
1 states contribution very sensitive to gpp
(2???)
56
Fixing gpp
SSD
ft-value supports gpp 0.85
Some tension in fixing to observed half-lives or
ft-values
116Cd ? 116In ? 116Sn
57
ft-values
Some existing data not that good, if available at
all? new measurements at TRIUMF using ion traps