1. Double Beta Decay Present and Future
Jenny Thomas
Rencontres du Vietnam, 2004
Jenny Thomas

2. Preview Introduction: why search for 0nbb decay?
Status of the search today: 3 experiments
Cuoricino
NEMO-III
Heidleberg-Moscow : signal!
Look at parameter space for 0nbb experiments
Highlights of a few experiments on the horizon
Conclusions
J.Thomas, UCL

3. Introduction: oscillations
The neutrino mixing matrix looks like this:
From KamLAND, SNO, Super-K (Gonzales-Garcia NOON)
J.Thomas, UCL

4. Introduction:oscillations
mmin ~ eV
mmin ~ eV
J.Thomas, UCL

5. Introduction:double beta decay
Large number of even-even nuclei undergo double-beta decay, but not single-beta decay
Standard Model process of 2nbb is also allowed of course
Enrichment procedure in place for about 10 isotopes
You do not search for peaks in unknown places: you always know where to look
Q value of the decay is well known (difference in energy between two isotopes)
2nbb nbb
J.Thomas, UCL

6. Introduction:double beta decay
76Ge example
Qbb
Endpoint
Energy
J.Thomas, UCL

7. Introduction:the experiments
Two classes of approach to the experiment:
Detector IS the isotope
Ionisation detectors
Bolometer detectors
TPCs
Detector Contains the isotope(s)
Tracking detectors
Measure half life, infer mn
Half life sensitivity given by experimental details
G-phase space, exactly calculable:G0n ~ Qbb5
M0n-Nuclear Matrix Element, hard to calculate
Uncertain to factor 2-10, isotope dependent
Motivation to measure several isotopes
J.Thomas, UCL

8. Introduction:the isotopes
What are the usable bb decay isotopes?
76Ge, Q=2.038MeV : MG = x
48Ca,Q = 4.272MeV :MG = x
82Se, Q = 2.995MeV : MG = x
100Mo, Q = 3.034MeV :MG = x
116Cd,Q = 2.804MeV :MG = x
130Te,Q = 2.528MeV :MG = x
136Xe,Q = 2.481MeV :MG = x
150Nd,Q = 3.368MeV: MG = x
These can all be enriched by standard processes
J.Thomas, UCL

9. A History Plot mscale ~ 0.01 – 0.05 eV from oscillation experiments
TeO2
mscale ~ 0.01 – 0.05 eV from
oscillation experiments
J.Thomas, UCL

10. Where are we today?
People have been searching for double beta decay for many years : first suggested in 1937
Presently three experiments taking data
CUORICINO : Bolometer
NEMO-III: Tracking
HEIDLEBERG-MOSCOW : Ionization Ge detector
New improved Heidelberg-Moscow result shows 4.2s effect!
Cuoricino and NEMO-III will reach this sensitivity
J.Thomas, UCL

11. Today:CUORICINO Located in LNGS, Hall A CUORE R&D (Hall C)
CUORE (Hall A)
Cuoricino (Hall A)
J.Thomas, UCL

12. Today: CUORICINO 40.7kg total 34% natural abundance
2 modules, 9 detector each,
crystal dimension 3x3x6 cm3
crystal mass 330 g
9 x 2 x 0.33 = 5.94 kg of TeO2
heat bath
Thermal sensor
absorber
crystal
11 modules, 4 detector each,
crystal dimension 5x5x5 cm3
crystal mass 790 g
4 x 11 x 0.79 = kg of TeO2
Incident particle
J.Thomas, UCL

13. Today:CUORICINO
J.Thomas, UCL

14. Today:CUORICINO 130Te crysals in LNGS Q = 2.528MeV
Operation started early 2003
Background 0.19 counts/kev/kg/y
Energy resolution ~ 4eV at 2MeV
T1/2>7.5x1023 years
<mn>= eV : indicates large range of NME calculations available!
J.Thomas, UCL

15. Today: NEMO-III Located in Frejus Underground Lab AUGUST 2001
J.Thomas, UCL

16. bb decay isotopes in NEMO-3 detector
bb2n measurement
116Cd g
Qbb = keV
96Zr g
Qbb = 3350 keV
150Nd g
Qbb = keV
48Ca g
Qbb = 4272 keV
130Te g
Qbb = 2529 keV
External bkg
measurement
100Mo kg
Qbb = 3034 keV
82Se kg
Qbb = 2995 keV
natTe g
Cu g
bb0n search
(All the enriched isotopes produced in Russia)
Dominique Lalanne for the NEMO-3 Collaboration ICHEP 2004 Beijing August 16-21, 2004
J.Thomas, UCL

17. bb events selection in NEMO-3
Typical bb2n event observed from 100Mo
Run Number: 2040
Event Number: 9732
Date:
Vertex
emission
Vertex
emission
Deposited energy:
E1+E2= 2088 keV
Internal hypothesis:
(Dt)mes –(Dt)theo = 0.22 ns
Common vertex:
(Dvertex) = 2.1 mm
(Dvertex)// = 5.7 mm
J.Thomas, UCL

18. 100Mo 22 preliminary results
(Data 14 Feb – 22 Mar. 2004)
Sum Energy Spectrum
Angular Distribution
NEMO-3
events
6914 g
241.5 days
S/B = 45.8
NEMO-3
events
6914 g
241.5 days
S/B = 45.8
100Mo
100Mo
Data
22
Monte Carlo
Data
Background
subtracted
22
Monte Carlo
Background
subtracted
E1 + E2 (keV)
Cos()
T1/2 = 7.72 ± 0.02 (stat) ± 0.54 (syst)  1018 y
4.57 kg.y
Dominique Lalanne for the NEMO-3 Collaboration ICHEP 2004 Beijing August 16-21, 2004
J.Thomas, UCL

19. 100Mo 22 Single Energy Distribution HSD SSD
HSD, higher levels
contribute to the decay
SSD, 1+ level
dominates in the decay
(Abad et al., 1984,
Ann. Fis. A 80, 9)
100Mo 0+
100Tc 1+
Single electron spectrum different
between SSD and HSD
Simkovic,
J. Phys. G, 27, 2233, 2001
Esingle (keV)
NEMO-3
4.57 kg.y
E1 + E2 > 2 MeV
NEMO-3
4.57 kg.y
E1 + E2 > 2 MeV
Data
Data
22 SSD
Monte Carlo
22 HSD
Monte Carlo
HSD
higher levels
SSD
Single State
Background
subtracted
Background
subtracted
2/ndf = 139. / 36
2/ndf = 40.7 / 36
Esingle (keV)
Esingle (keV)
HSD: T1/2 = 8.61 ± 0.02 (stat) ± 0.60 (syst)  1018 y
SSD: T1/2 = 7.72 ± 0.02 (stat) ± 0.54 (syst)  1018 y
100Mo 22 single energy distribution
in favour of Single State Dominant (SSD) decay
Dominique Lalanne for the NEMO-3 Collaboration ICHEP 2004 Beijing August 16-21, 2004
J.Thomas, UCL

20. Today:NEMO-III Present 90%CL limits from NEMO-III(216.4 days)
82Se:T1/2(bb0n) > y, mn < 1.3 – 3.6 eV
Simkovic et al., Phys. Rev. C60 (1999)
Stoica, Klapdor, Nucl. Phys. A694 (2001)
Caurier et al., Phys. Rev. Lett (1996)
100Mo T1/2(bb0n) > y, mn < 0.7 – 1.2 eV
Expected Reach in 5 years after RadonPurification
100Mo T1/2(bb0n) > y, mn < 0.2 – 0.35 eV
82Se:T1/2(bb0n) > y,,mn < 0.65 – 1.8 eV
J.Thomas, UCL

21. Today: Heidelberg-Moscow
Enriched Germanium ionisation detector
J.Thomas, UCL

22. Today: Heidelberg-Moscow
New analysis provides evidence of a peak at the expected value
Total 71.7kgy of data
Significance is 4.2 s
mn = eV
Corresponds to quasi-degenerate neutrino masses
J.Thomas, UCL

23. Present Cuoricino/NEMO-III region
Possible evidence (best value 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/
J.Thomas, UCL

24. Future Plans Only a few approaches
Bolometers: Isotope is the detector
Tracking : Isotope inside the detector
Ionisation : Isotope is the detector
Simple formula relates experimental parameters to half life reach: background or no background:
a-isotopic abundance,b-background/Kev/kg/y,e-efficiency,dE-energy resolution,t-time,W-molecular weight,m-mass
J.Thomas, UCL

25. Future Plans
There are presently 16 projects in various stages of planning/approval in Italy,Japan,US,France and perhaps other places, target eV in mass
Tracking, TPC, Drift
DCBA Nd
MOON Mo
Super-NEMO Mo,Se,Nd
EXO Xe
Ionisation
Cobra, CdTe
GEM
GENIUS
Majorana
MPI
Scintillator
CAMEO Cd
GANDLES Ca
CARVEL Cd
GSO Gd
Xe Xe…….
Highlight reach of a few
CUORE, 720kg TeO2, bolometers
EXO, 1Tonne Xenon, TPC amd +Ba identification
MAJORANA, 500kg Ge, ionization
Super-NEMO several isotopes, tracking
J.Thomas, UCL

26. Future Plans : CUORE First fully-funded next generation experiment
Based on CUORICINO technology, 130TeO2
Located at LNGS
Target background 0.001c/kev/kg
720kg of TeO2
J.Thomas, UCL

27. Future Plans : EXO
High Pressure Xe TPC with laser tagging of +Ba daughter for background-free measurement
2 Tonne of 136Xe at 10Atm or Liq Xe with cold-finger tagging
Energy resolution 2% at 2.5MeV
200kg prototype of Liq Xe funded by DoE (no tagging) will be built at WIPP, New Mexico.
200kg isotope already in hand
J.Thomas, UCL

28. Future Plans : Majorana/MPI
500kg enriched segmented conventional Ge detector
Feasability has been demonstrated, waiting for approval
Will use pulse-shape information to reduce background
Based on theory that dominant background is 68Ge from cosmogenics
MPI-Ge experiment also proposed
Uses Ge mono-crystal in Liquid N or Ar for passive/active shielding
Based on theory that dominant background is from Cu etc external to Ge
J.Thomas, UCL

29. Future Plans : Super-NEMO
Based on NEMO-III technology,SM only background
study Se,Nd,Mo, low SM background
Design study will start 2005
Feasible if:
BG only from 2n bb
(NEMO3)
b) DE/E = 10% at 1 MeV
(8% has already been demonstrated in recent R&D)
J.Thomas, UCL

30. Future Plans Certain factors dominate reach
Some factors are instrinsic to a particular isotope (M), others to the experimental approach
T01/2 given by experimental parameters:background,resolution,efficiency
The larger M, the lower the reach in mn
J.Thomas, UCL

31. weighted world average NMEs a la Frank Avigone, Neutrino 2004
Future Plans : Summary
weighted world average NMEs a la Frank Avigone, Neutrino 2004
J.Thomas, UCL

32. Conclusions
Very exciting time for neutrino physics in general and 0nbb in particular
A positive signal is now a serious possibility in light of oscillation results
Costs of experiemnts all in the $50M range: this is small potatoes for the potential scientific gain
In light of large NME uncertainties, several isotopes should be measured to avoid disappointment
J.Thomas, UCL