# StAndrews_2006_lect2_orig

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```					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
Nuclear matrix elements

The dark side of double beta decay
Nuclear matrix elements

F. Simkovic
Uncertainties   F. Simkovic
Uncertainties   F. Simkovic
Reminder
2              0
Multipoles
0: All intermediate states contribute

How to explore those???
Charge exchange reactions
2: Only intermediate 1+ states contribute
Supportive measurements
from accelerators

Currently: (d,2He) and (3He,t)
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...
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
Can you prove that  is Dirac?
Answer: Show that neutrinos have a static magnetic momentt

Energy in field:    Eem     B  d   E
CPT changes sign of spin, thus Eem=-Eem, bu they must be thee
same for Majorana neutrinos. Hence   d  0

 eL  ee e  eR 

                 
e
 

 eR      R 
                   

3GF e              19 m 
          m  3.2 10   B  
            8 2  2
eV 
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
The search for 0
or
Phase space
0decay rate scales with Q5

2 decay rate scales with Q11
Q-value Nat. abund. (PS 0v)–1       (PS 2v) –1
Isotope
(keV)                  (yrs x eV2)   (yrs)
(%)
Ca 48     4271        0.187       4.10E24     2.52E16
Ge 76     2039        7.8         4.09E25     7.66E18
Se 82     2995        9.2         9.27E24     2.30E17
Zr 96     3350        2.8         4.46E24     5.19E16
Mo 100    3034        9.6         5.70E24     1.06E17
Pd 110    2013        11.8        1.86E25     2.51E18
Cd 116    2802        7.5         5.28E24     1.25E17
Sn 124    2288        5.64        9.48E24     5.93E17
Te 130    2529        34.5        5.89E24     2.08E17
Xe 136    2479        8.9         5.52E24     2.07E17
Nd 150    3367        5.6         1.25E24     8.41E15
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, ...
Spectral shapes
0: Peak at Q-value of nuclear transition

Measured quantity: Half-life

Dependencies (BG limited)
T1/2  a •  (M•t/E•B)1/2

1 / T1/2 = PS * ME2 * (m / me)2

Sum energy spectrum of both electrons
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 •  (M•t/E•B)1/2             N   BEMt
• a: isotopical abundance        B
• M: mass
• t: measuring time                     
• E: energy resolution
Q-E/2 Q Q+E/2       E
• B: background (c/keV/kg/yr)
Signal information
(A,Z)  (A,Z+2) + 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,Z+2)
Gamma rays (eg. four 511 keV photons in ++)
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
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
Geochemical approach
Major advantage: Experiment is running since a billion years
Signal: Isotopical anomaly        N(Z  2, A) 1 T: age of ore

N(Z, A) T

Practically search has been possible due to the high sensitivity of
noble gas mass spectrometry. Thus daughter should be noble gas.


You cannot discriminate
2 from 0
T. Kirsten et al, PRL 20 (1968)
Experimental techniques
Source = detector        Source  detector

Semiconductors          Time projection chambers (TPC)
Heidelberg-Moscow, IGEX,      NEMO-3, SuperNEMO,
COBRA, GERDA, MAJORANA        DCBA, EXO
Cryogenic bolometers
CUORICINO, CUORE
Scintillators
SNO+, CANDLES, MOON,
GSO, XMASS
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
0 peak region
t
r
c
e

u
p
S

m
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 > 1.9 x 1025 yr (90% CL)                   m < 0.35 eV
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)

F. Feruglio et al., hep-ph/0201291
C.A. Aalseth et al., hep-ex/0202018

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)
Heidelberg -Moscow

more statistics

Recalibration

Subgroup of collaboration                                            m = 0.17 - 0.63 eV
T1/2 = 0.6 - 8.4 x 1025 yr

H.V. Klapdor-Kleingrothaus et al, Phys. Lett. B 586, 198 (2004)
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)
 Check with a different isotope
Uncertainties in nuclear matrix elements, example 116Cd
<m>=0.4eV

V. Rodin et al., nucl-th/0503063, Nucl. Phys. A 2006
CUORICINO-CUORE - Principle
Heat sink

Thermal coupling
Thermometer
Double beta decay

Crystal absorber

example: 750 g of TeO2 @ 10 mK
C ~ T 3 (Debye)  C ~ 2×10-9 J/K
1 MeV -ray      T ~ 80 K
 U ~10 eV
CUORICINO - Spectrum
0DBD

Gamma region,
Alpha region, dominated by alpha peaks
dominated by gamma
and beta events,       (internal or surface contaminations)
highest gamma line =
2615 keV 208Tl line
(from 232Th chain)
CUORICINO - Results
208Tl
60Co   sum
130Te   DBD
T1/2 > 2.4 x 1024 yrs
(90% CL)

m < 0.2-1.1 eV
CUORICINO-CUORE
19 towers
13x4 crystals/tower

Future: CUORE 760 kg TeO2 approved
NEMO-3
Only approach with source different from detector
 decay isotopes in NEMO-3 detector

2 measurement
116Cd   405 g
Q= 2805 keV

96Zr     9.4 g
Q= 3350 keV

150Nd   37.0 g
Q= 3367 keV

48Ca      7.0 g
Q= 4272 keV

130Te    454 g
Q= 2529 keV
External bkg
100Mo                  82Se                   natTe   491 g
6.914 kg             0.932 kg                            measurement
Q= 3034 keV         Q= 2995 keV
Cu      621 g

0 search
NEMO-III - Event
Typical 2 event of 100Mo
100Mo      results
7.37 kg.y
(Data Feb. 2003 – Dec. 2004)

Sum Energy Spectrum                                  Angular Distribution

NEMO-3              219 000 events                                     219 000 events
NEMO-3
6914 g                                             6914 g
100Mo                       389 days                    100Mo                  389 days
S/B = 40                                           S/B = 40
•   Data
22
•   Data                                 Monte Carlo
22                                     Background
Monte Carlo                              subtracted
Background
subtracted

E1 + E2 (keV)                                              Cos()

2: T1/2 = 7.11  0.02 (stat)  0.54 (syst)  1018 y
0: T1/2 > 5.8 x 1023 yrs (90% CL) m < 0.6 - 2.8 eV
R. Arnold et al, PRL 95 (2005)                      Idea: SuperNEMO (100 kg)
SuperNEMO
Idea: Use 100 kg enriched 82Se
source
tracker
calorimeter

1m           4m

5m
Top view                 Side view
COBRA

Use large amount of
CdZnTe
Semiconductor Detectors

Array of 1cm3
CdTe detectors

K. Zuber, Phys. Lett. B 519,1 (2001)
Isotopes
nat. ab. (%) Q (keV)   Decay mode

Zn70        0.62     1001       ß-ß-
Cd114       28.7     534        ß-ß-
Cd116       7.5      2809       ß-ß-
Te128       31.7     868        ß-ß-
Te130       33.8     2529       ß-ß-
Zn64        48.6     1096       ß+/EC
Cd106       1.21     2771       ß+ß+
Cd108       0.9      231        EC/EC
Te120       0.1      1722       ß+/EC
• 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“)
2 - decay
2 is ultimate, irreducible background
Energy resolution extremely important
check whether people use FWHM or  (there is a factor 2.35 difference)
8Q(E /Q) 6
Fraction of 2 in 0 peak: F              3.7 *10 10
me
S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci. 2002

Signal/Background:
                       S 1 T12
    /2
0
 433
B F T1/ 2
T12  3.2  10 19 yrs
/2

T10  2  10 26 yrs
/2
The first layer
4x4x4 detector array = 0.42 kg CdZnTe semiconductors

Installed at LNGS about three month ago
The solid state TPC
Energy resolution            Tracking

• Massive background
Reduction (Particle-ID)
• Positive signal
information
Pixellated CdZnTe detectors
Pixellisation - I
• Particle ID possible, 200m pixels (example simulations):
= 1 pixel,  and = several connected pixel, = some disconnected p.

3 MeV 
0                                

~15m

1-1.5mm

• eg. Could achieve nearly 100% identification of 214Bi events
(214Bi  214Po  210Pb)
Beta with        7.7MeV 
.                             endpoint         life-time =
3.3MeV          164.3s
Pixellated detectors
Solid state TPC

3D - Pixelisation:
Nobody said it was going to be easy, and nobody was right
George W. Bush
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
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, ...
Future projects, ideas                        Status 2006

small scale ones will expand, very likely not a complete list...
Future - Ge approaches
MAJORANA
500 kg of enriched
Ge detectors               GERDA

Naked enriched Ge-crystals in
Segmentation and                 LAr with lead shield
pulse shape
discrimination
20 kg enriched Ge-detectors
at hand (former HD-MO and
IGEX), 35 kg enriched bought
MERGE
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
Summary
Double beta decay is the gold plated channel to probe
the fundamental character of neutrinos
Taking current evidences from oscillation data it is
likely to be the only way to fix the absolute neutrino mass
To go below 50 meV requires hundreds of kilograms of
enriched 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 to
disentangle the physics mechanism we need at least 3(4)
isotopes measured
Hope....
Particle particle coupling gpp
1+ states contribution very sensitive to gpp (2)
Fixing gpp

SSD

ft-value supports gpp = 0.85

Some tension in fixing to observed
116Cd    116In  116Sn     half-lives or ft-values
ft-values

Some existing data not that good, if available at all
 new measurements at TRIUMF using ion traps

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