1. Future Zero-Neutrino Double Beta Decay Experiments
Outline
Neutrino Mass and bb
General Experimental Issues
The Matrix Elements
The New Proposals
Steve Elliott, UK Forum 2003

2. Neutrino Mass: What do we want to know?
Relative
Mass
Scale
Absolute
Mass
Scale
Dirac or Majorana ne n1 n2 n3
Mixing
Steve Elliott, UK Forum 2003

3. 3 Complementary Experimental Techniques
Need all three types of experiments to
fully understand the nature of the n.
Steve Elliott, UK Forum 2003

4. Neutrino Masses <mb> < 2.2 eV Sets mn scale > 50 meV
Direct mass and bb experiments set absolute mass scale.
<mb> < 2.2 eV
The results of oscillation experiments set the relative mass scale.
Sets mn scale > 50 meV
bb addresses Dirac/Majorana nature of n.
Steve Elliott, UK Forum 2003

5. Example Decay Scheme In many even-even nuclei, b decay is
Endpoint
Energy
In many even-even nuclei, b decay is
energetically forbidden. This leaves bb
as the allowed decay mode.
Steve Elliott, UK Forum 2003

6. bb(2n): Allowed and observed 2nd order weak process.
bb(2n) vs. bb(0n)
bb(2n): Allowed and observed 2nd order weak process.
bb(0n): requires massive Majorana neutrinos even in presence of alternative mechanisms.
Steve Elliott, UK Forum 2003

7. Energy Spectrum for the 2 e-
Endpoint
Energy
Steve Elliott, UK Forum 2003

8. bb Decay Rates G are calculable phase space factors. G0n ~ Q5
|M| are nuclear physics matrix elements.
Hard to calculate.
mn is where the interesting physics lies.
Steve Elliott, UK Forum 2003

9. What about mixing, mn & bb(0n)?
No mixing:
virtual n exchange
e = ±1, CP cons.
Mbb is a coherent sum because the neutrino is virtual.
Mv is an incoherent sum because the neutrinos are real.
Compare to b decay result: real n emission
Steve Elliott, UK Forum 2003

10. From KamLAND, solar n and atmospheric n
Neutrino Mixing
From KamLAND, solar n and atmospheric n
Steve Elliott, UK Forum 2003

11. Min. <mbb> as a vector sum
<mbb> is the modulus of the resultant vector in the complex plane. (In this example, <mbb> has a min. It cannot be 0.)
min
Figure from: PR D63,
Steve Elliott, UK Forum 2003

12. More General: 3 n (Inverted Heir.)
<mbb>
30 meV or
few x 1027 yr
Plot
Thanks to
Petr Vogel
msmallest
Steve Elliott, UK Forum 2003

13. More General: (Normal Heir.)
30 meV or
few x 1027 yr
Plot
Thanks to
Petr Vogel
Steve Elliott, UK Forum 2003

14. Physics Reach Solar + KamLAND + Atmospheric (Ue3~ 0) Normal Hierarchy
Inverted Hierarchy
Degenerate
m1 ~ 0 meV
~55 meV
= M > about 100 meV
m2 ~ 7 meV M
m3 ~ 55 meV
~0 meV
<mbb> ~ 5 meV
28 or 55 meV
M/2 or M
Solar + KamLAND + Atmospheric (Ue3~ 0)
Steve Elliott, UK Forum 2003

15. For the next experiments:
An exciting time for bb!
For at least
one neutrino:
For the next experiments:
< mbb > in the range of
10 - 50 meV is very interesting.
Steve Elliott, UK Forum 2003

16. <mbb> History
1948 Earliest measurements by Fireman used Geiger counter tube coincidence to look for 2 electrons..
Early 50ies, Cloud chamber experiments were an improvement
Mid fifties, the big step forward was the meausruement of the sum energy of the 2 electrons and looking for a peak.
~2015
|M| Reference
Eur. Lett. 13, 31 (1990)
Steve Elliott, UK Forum 2003

17. An Ideal Experiment Maximize Rate/Minimize Background
Large Mass (~ 1 ton)
Good source radiopurity
Demonstrated technology
Natural isotope
Small volume, source = detector
Good energy resolution
Ease of operation
Large Q value, fast bb(0n)
Slow bb(2n) rate
Identify daughter
Event reconstruction
Nuclear theory
Steve Elliott, UK Forum 2003

18. Classes of Background bb(2n) tail
Need good energy resolution.
Natural U, Th in source and shielding
Pure materials, identify bb daughter, pulse shape, timing, position.
Cosmic ray activation
Store and prepare materials underground.
Steve Elliott, UK Forum 2003

19. bb(2n) as a Background. Sum Energy Cut Only
next generation
experimental
goal
Steve Elliott, UK Forum 2003

20. Target: t(bb(0n) ~ 1027 years Cryostat, or other experimental support
Natural Activity
The Problem:
t(U, Th) ~ 1010 years
Target: t(bb(0n) ~ 1027 years
Detector
Shielding
Cryostat, or other experimental support
Front End Electronics
etc.
Steve Elliott, UK Forum 2003

21. Cosmic Ray Induced Activity
Material dependent.
Need for depth to avoid activation.
Need for storage to allow activation to decay.
Steve Elliott, UK Forum 2003

22. Evidence of 68Ge
From: NIM A292 (1990)
Experimental data from two 1.05 kg natural detectors
Integral of this spectrum equals integral of this peak.
ROI
This peak decays with the right half life.
Steve Elliott, UK Forum 2003

23. Depth Requirement Remove Surface Activation
100 mwe, low E neutrons from rock
Muons
~30% of events in ROI vetoed at 2500 mwe
Muon-induced secondary activation
Still observed at low E at 2000 mwe.
For MOON-like natMo expt.,
~ Mo(n,2n)91Mo per year
m directly induced
OK at 4700 mwe (e.g. SAGE)
Unknown components
Deeper is better!
Steve Elliott, UK Forum 2003

24. There are many calculations.
Matrix Elements
There are many calculations.
Most authors quote mass limits derived from all or at least representatives of the whole range.
How do we interpret the uncertainty associated with the mass due to the nuclear physics?
Steve Elliott, UK Forum 2003

25. <mbb> Uncertainties
Imagine signal at 7x1026 years
500 kg for 10 years
~50% unc. for t1/2 (with BG)
~20% without BG
|M| Range: meV
Statistics (with BG): ±25 meV
Steve Elliott, UK Forum 2003

26. Statistical contribution contribution to uncertainty.
Consider a 100 meV result.
Statistical contribution
to uncertainty.
Our conclusion about the possible range of m1 would be greatly affected by this uncertainty. In fact if coupled with a fortuitous beta decay measurement the possibility to exclude the inverse hierarchy could be lost.
Matrix Element
contribution to uncertainty.
Would this exclude the inverted hierarchy with small msmallest?
Need improvement in the Theory.
Steve Elliott, UK Forum 2003

27. “Found” Peaks Need more than one experiment A 2527-keV Ge-det.
PR D45, 2548 (1992)
A 2527-keV Ge-det.
peak that was an
electronic artifact.
NP B35 (Proc. Supp.), 366 (1994).
A ~2528-keV Te-det. peak that was a 2s
Statisticalflucuation.
Steve Elliott, UK Forum 2003

28. A Great Number of Proposed Experiments
COBRA
Te-130
10 kg CdTe semiconductors
DCBA
Nd-150
20 kg Nd layers between tracking chambers
NEMO
Mo-100, Various
10 kg of bb isotopes (7 kg of Mo)
CAMEO
Cd-114
1 t CdWO4 crystals
CANDLES
Ca-48
Several tons CaF2 crystals in liquid scint.
CUORE
750 kg TeO2 bolometers
EXO
Xe-136
1 ton Xe TPC (gas or liquid)
GEM
Ge-76
1 ton Ge diodes in liquid nitrogen
GENIUS
GSO
Gd-160
2 t Gd2SiO5:Ce crystal scint. in liquid scint.
Majorana
500 kg Ge diodes
MOON
Mo-100
Mo sheets between plastic scint., or liq. scint. Xe
1.56 t of Xe in liq. Scint.
XMASS
10 t of liquid Xe
Steve Elliott, UK Forum 2003

29. Potential Large-Mass (~1 ton) Future Experiments
Experiments in Europe
CUORE, GENIUS
NUSEL Candidates
EXO*, MAJORANA, MOON
Smaller Mass and Development Experiments Cobra*, DCBA, NEMO*, CAMEO, CANDLES, GSO…
Steve Elliott, UK Forum 2003

30. The MOON Collaboration:
H.Ejiri, Y. Itahashi, N. Kudomi, M. Nomachi, T. Shima
RCNP, Osaka Univ. Japan
R. Hazama, K. Matsuoka, Y. Sugaya, S. Yoshida
Phys. Dept. Osaka Univ. Japan
K. Fushimi, K. Ichihara, Y. Shichijo
University of Tokushima, Japan
P.J. Doe, V. Gehman, R.G.H. Robertson, O. E. Vilches, J.F. Wilkerson, D.I. Will
CENPA, Univ. Washington Seattle, USA
S.R. Elliott,
LANL, USA
J. Engel
Univ. North Carolina, USA
A. Para,
FNAL, USA
M. Greenfield,
International Christian Univ., USA
M. Finger
Phys. Dept., Charles Univ., Prague, Czech Republic
A. Gorin, I.Manouilov, A. Rjazantsev
Inst. High Energy Physics, Protvino, Russia
K. Kuroda, P. Kavitov, V. Vatulin,
VNIIEF, Sarov, Russia
V. Kekelidze, V. Kutsalo, G. Shirkov, A. Sisakian,
A. Titov, V. Voronov,
JINR, Dubna, Russia
In Association with:
The Majorana Collaboration
C. Aalseth, F. Avignone,
S.R. Elliott, H. Miley…...
Steve Elliott, UK Forum 2003

31. MOON is 4 experiments… 100Mo  100Tc 100Mo CC Solar n 100Ru 100Ru ?
0.168 
100Tc
100Mo
16 s
1.00 x 1019 y
-3.034
CC Solar n
100Ru
-3.034
100Ru
?
100Mo
-1.293 
H. Ejiri et al. PRL 85 (2000) 2917
6.1 x 1020 y
-1.904
100Ru
Hamish Robertson APS, April 5, 2003
Steve Elliott, UK Forum 2003

32. Signal Rates per year per ton of 100Mo
0nbb (ground state)
20 (<m> / 50 meV)2
2nbb (ground state)
3.6 x 108
0nbb (0+1 state)
.03 (<m> / 50 meV)2
2nbb (0+1 state)
0nbb (0+2 state)
6.9 x 106
.5 (<m> / 50 meV)2 pp
120
7Be 40
pep
2.5 8B
5.1
13N
4.2
15O
6.1 * * *
SSM
rates
*QRPA: J. Souhonen, NP A700, 649 (2002).
76Ge : 3.8 (<m> / 50 meV)2
Steve Elliott, UK Forum 2003

33. MOON Overview 3.3 tons 100Mo, 34 tons Mo
Doesn’t require enriched material (but would probably want it).
Scintillator/source sandwich
Position and single Eb data play big role in bb(2n) and U, Th rejection. Or possibly bolometer
14% efficiency
ELEGANTS is precursor.
Steve Elliott, UK Forum 2003

34. Detection Techniques under Consideration:
Scintillator Mo Foil Sandwich
Mo loaded liquid scintillator
Cryogenic calorimeter
One possible configuration
scintillator
Readout fibers
Mo foil
1 module:
Mo foil, 6m x 6m x 0.05 gm/cm
Scintillator 6m x 6m x 0.25cm
222 wavelength shifting fibers
Super module (detector)
1950 Modules
6m x 6m x 5m
34 t nMo (3 t 100Mo)
13600, 16-anode PMT readout
Steve Elliott, UK Forum 2003

35. MOON Prototype
Steve Elliott, UK Forum 2003

36. Cryogenic Underground Observatory for Rare Events - CUORE
Berkeley
Firenze
Gran Sasso
Insubria (COMO)
Leiden
Milano
Neuchatel
U. of South Carolina
Zaragoza
Spokesperson
Ettore Fiorini
Milano
Steve Elliott, UK Forum 2003

37. CUORE Overview 0.21 ton, 34% natural abundance 130Te
TeO2 bolometers, 750 g crystals
Doesn’t require enriched material.
1020 5x5x5 cm3 crystals
25 towers of 10 layers of 4 crystals
Gran Sasso Laboratory
CUORICINO is an approved prototype (1 tower).
CUORICINO began operation in Feb. 2003
Steve Elliott, UK Forum 2003

38. CUORE Detector Detector Damping Suspension Dilution Unit Thermal
Shields
Steve Elliott, UK Forum 2003

39. CUORICINO IS OPERATING
FIRST PULSE.
Data runs began
In Feb. 2003
Steve Elliott, UK Forum 2003

40. Enriched Xenon Observatory - EXO
U. of Alabama
Caltech
IBM Almaden
ITEP Moscow
U. of Neuchatel
INFN Padova
SLAC
Stanford U.
U. of Torino
U. of Trieste
WIPP Carlsbad
Spokesperson
Giorgio Gratta
Stanford
Steve Elliott, UK Forum 2003

41. EXO Overview (latter talk)
10 ton, ~70% enriched 136Xe
70% effic., ~10 atm gas TPC or LXe chamber
Optical identification of Ba ion.
Drift ion in gas to laser path
or extract on cold probe to trap.
TPC performance similar to that at Gottard.
100-kg enrXe prototype (no Ba ID)
Isotope in hand
Steve Elliott, UK Forum 2003

42. The Majorana Project Co-Spokespersons Frank Avignone Harry Miley
Duke U.
North Carolina State U.
TUNL
Argonne Nat. Lab.
JINR, Dubna
ITEP, Moscow
New Mexico State U.
Pacific Northwest Nat. Lab.
U. of Washington
LANL
LLNL
U. of South Carolina
Brown
Univ. of Chicago
RCNP, Osaka Univ.
Univ. of Tenn.
Co-Spokespersons
Frank Avignone
Harry Miley
Steve Elliott, UK Forum 2003

43. Majorana Overview 0.5 ton of 86% enriched 76Ge
Segmented detectors using pulse shape discrimination to improve background rejection.
Prototype ready to go this fall/winter. (14 crystals, 1 enriched)
100% efficient
Can do excited state decay.
IGEX is precursor
Steve Elliott, UK Forum 2003

44. Majorana Layout
Steve Elliott, UK Forum 2003

45. AGe + fast n -> 68Ge + X 68Ge 68Ga 68Zn
288d
68Ge
68Ga
68Zn
2.9 MeV
68Ge is the dominate background.
For 500-kg enriched detector, initially
expect ~500 68Ge decays/day. t1\2 = 288 d
The naturally occurring 40K in the human
body decays at a rate of decays/second.
Steve Elliott, UK Forum 2003

46. Why Segmentation and Pulse Shape Analysis?
bb is pointlike.
b+ or Compton scattered
g rays deposit energy in
multiple locations.
Segmentation and PSD
help reduce these
Backgrounds.
Steve Elliott, UK Forum 2003

47. Recent Crystal Packaging Test (MEGA)
Steve Elliott, UK Forum 2003

48. GErmanium NItrogen Underground Setup - GENIUS
MPI, Heidelberg
Kurchatov Inst., Moscow
Inst. Of Radiophysical Research, Nishnij Novgorod
Braunschweig und Technische Universität, Braunschweig
U. of L'Aquila, Italy
Int. Center for Theor. Physics, Trieste
JINR, Dubna
Northeastern U., Boston
U. of Maryland, USA
University of Valencia, Spain
Texas A & M U.
Spokesperson
Hans Klapdor-Kleingrothaus
MPI
GENIUS
Steve Elliott, UK Forum 2003

49. GENIUS Overview 1 ton, ~86% enriched 76Ge Naked Ge crystals in LN
Very little material near Ge.
1.4x106 liters LN
40 kg test facility is approved.
100% efficient
Heid.-Moscow experiment is precursor
GENIUS
Steve Elliott, UK Forum 2003

50. GENIUS Layout
Clean Room
Data
Acquisition
Insulation
Liquid
Nitrogen
Setup for operation of three 'naked’ Germanium detectors in liquid nitrogen.
Steel
Vessel
12 m
GENIUS
Steve Elliott, UK Forum 2003

51. A Recent Claim for bb(0n)
Mod. Phys. Lett. A16, 2409 (2001)
Steve Elliott, UK Forum 2003

52. The Controversy.
Locations of
claimed peaks
Mod. Phys. Lett. A16, 2409 (2001)
If one had to summarize the controversy in a short statement:
Consider two extreme background models:
1. Entirely flat in keV region.
2. Many peaks in larger region, only bb peak in small region.
These 2 extremes give very different significances for peak at 2039 keV.
KDHK chose Model 2 but did not consider a systematic uncertainty
associated with that choice.
Steve Elliott, UK Forum 2003

53. Summary of Proposals
The <mbb> limits depend on background assumptions and matrix elements which vary from proposal to proposal.
Steve Elliott, UK Forum 2003

54. UG Lab space will be needed for some of that R&D.
Conclusions
Research and Development are needed for all the future proposed detectors.
UG Lab space will be needed for some of that R&D.
The next generation bb experiments have a good possibility of reaching an interesting <mbb> region.
Steve Elliott, UK Forum 2003

55. Pulse Shape Discrimination
Steve Elliott, UK Forum 2003