1. Double Beta experiment using nuclear emulsions?
M. Dracos
Double Beta experiment using nuclear emulsions?
Marcos Dracos
IPHC/IN2P3, Université de Strasbourg
M. Dracos, Osaka, 26/05/2010

2. M. Dracos
Double Beta Decay
M. Dracos, Osaka, 26/05/2010

3. Double Beta Decay L=0 L=2 T 1/2 ~ 1019-1020 years !
M. Dracos
Double Beta Decay
neutrinoless double beta
L=0
L=2
allowed double beta
T 1/2 ~ years !
Observed for: Mo100, Ge76, Se82, Cd116, Te130, Zr96, Ca48, Nd150
Qbb = Ee1 + Ee2 - 2me
T1/2= F(Qbb,Z) |M|2 <mn>2 -1
Phase space factor
Nuclear matrix element
Effective mass:
<mn>= m1|Ue1|2 + m2|Ue2|2.eia + m3|Ue3|2.eib
|Uei|: mixing matrix elements, a and b: Majorana phases 5
2 electron energy (keV)
M. Dracos, Osaka, 26/05/2010

4. Neutrino Oscillations
M. Dracos
Neutrino Oscillations
MNSP Matrix (Maki, Nakagawa, Sakata, Pontecorvo)
solar,
reactors
reactors
accelerators
CP violation
atmospheric,
accelerators
Majorana phases
Effective mass:
<mn>= m1|Ue1|2 + m2|Ue2|2.eia + m3|Ue3|2.eib
|Uei|: mixing matrix elements, a and b: Majorana phases
M. Dracos, Osaka, 26/05/2010

5. Neutrino mass hierarchy
M. Dracos
Neutrino mass hierarchy m2
m12
m22
m32
Degenerate
m1≈m2≈m3» |mi-mj|
Normal hierarchy
m3>>> m2~m1
Inverted hierarchy
m2~m1>>m3 ?
normal
inverted
M. Dracos, Osaka, 26/05/2010

6. Neutrino mass hierarchy
M. Dracos
Neutrino mass hierarchy
Inverted hierarchy
Normal hierarchy
Degenerate
Lightest neutrino (m1) in eV
| mee| in eV
Lower bounds!
Goal of next
generation
experiments:
~10 meV
M. Dracos, Osaka, 26/05/2010

7. Possible mechanisms of Double Beta decay
M. Dracos
Possible mechanisms of Double Beta decay
M. Dracos, Osaka, 26/05/2010

8. Possible mechanisms of Double Beta decay
M. Dracos
Possible mechanisms of Double Beta decay
0nbb can be generated by:
exchange of light Majorana neutrinos
SUSY
LR symmetric model …
these models are very often differentiated by the 2 electron angular distribution
where K varies from -1 to +1 according to the extension of the Standard Model
(A. Ali, A.V. Borisov, and D.V. Zhuridov, Phys. Rev. D 76, (2007))
M. Dracos, Osaka, 26/05/2010

9. Present detection techniques or under investigation
M. Dracos
Present detection techniques or under investigation
Calorimeter
Semi-conductors
Source = detector
Calorimeter
(Loaded) Scintillator
Source = detector
Tracko-calo
Source  detector
Xe TPC
Source = detector b b b b b b b b
e, DE
e, M
e,M
isotope choice
good energy resolution
better background rejection
CANDLES
NEMO3
CUORE
CaF2(Pure)
EXO
M. Dracos, Osaka, 26/05/2010

10. Bolometers (Cuorecino)
M. Dracos
Bolometers (Cuorecino)
Q-value for 0νββ in 130Te
± 2.0 keV
Double-Beta Decay in Tellurium 130
Heat sink
Thermal coupling
Thermometer
Decay
Crystal absorber
44 5x5x5 cm3 and 18 3x3x6 cm3 TeO2 crystals,
detector mass 40.7 kg,
130Te mass 11 kg
M. Dracos, Osaka, 26/05/2010

11. Candidate nuclei for double beta decay
M. Dracos
Candidate nuclei for double beta decay
For most of the
nuclei in this list
the 2νββ decay
has been observed
M. Dracos, Osaka, 26/05/2010

12. The NEMO3 detector (Fréjus tunnel)
M. Dracos
The NEMO3 detector (Fréjus tunnel)
Calorimetry combined with electron tracking
Advantage:
detection of the 2 electrons
background rejection a b g
electronic noise …
M. Dracos, Osaka, 26/05/2010

13. The NEMO3 detector (Fréjus tunnel)
M. Dracos
The NEMO3 detector (Fréjus tunnel)
with magnetic field
expected sensitivity up to mn~0.3 eV
plastic scintillator blocks 3m +
photomultipliers (Hamamatsu 3", 5")
wire chamber
(Geiger)
energy and time of flight measurements
Sources :
10 kg, 20 m2
2 electron tracks
low radioactivity materials
M. Dracos, Osaka, 26/05/2010

14. The NEMO3 detector NEMO3 detector inside aradon tente Sources :
M. Dracos
The NEMO3 detector
NEMO3 detector inside aradon tente
Sources :
10 kg, 20 m2
M. Dracos, Osaka, 26/05/2010

15. Isotopes isotopes used by NEMO3 experiment at Fréjus Isotope Q(keV)
M. Dracos
Isotopes
Isotope
Q(keV)
116Cd116Sn
2804.74.2
82Se82Kr
2995.23.3
100Mo100Ru
3034.86.3
96Zr96Mo
3350.03.5
150Nd150Sm
3367.14.9
48Ca48Ti
4272.04.1
Bckg
sourcesthicknessmg/cm2)
82Se (0,93 kg)
isotopes used by NEMO3 experiment at Fréjus
M. Dracos, Osaka, 26/05/2010

16. Typical ~1 MeV 2nbb candidate event
M. Dracos
Event Examples
Trigger
1 PMT > 150 keV
3 Geiger cells (2 neighbours + 1)
Trigger rate ~7 Hz
Main criteria
2 tracks with Q < 0
common vertex
internal event from the foil (TOF cut)
No unassociated PMT ( rejection)
No delayed short tracks ( rejection from 214Bi-214Po cascade)
rate: 1 event / 2.5 minutes
Typical ~1 MeV 2nbb candidate event
M. Dracos, Osaka, 26/05/2010

17. M. Dracos
Event Examples
M. Dracos, Osaka, 26/05/2010

18. Main sources of Background
M. Dracos
Main sources of Background
Many ways to mimic a bb signal
Natural radioactivity
U/Th chains (Rn),
40K
Cosmic m
Neutrons
Artificial radioactivity
M. Dracos, Osaka, 26/05/2010

19. Results T1/2(bb0n) > 5.8 1023 (90 % C.L.)
M. Dracos
Results
932 g
389 days
2750 even.
S/B = 4
Phase I + II
693 days
T1/2(bb0n) > (90 % C.L.)
 <mn> < eV
100Mo
( 7 kg )
82Se
Expected in 2009
T1/2(bb0n) > (90 % C.L.)
 <mn> < eV
82Se T1/2 = 9.6 ± 0.3 (stat) ± 1.0 (syst)  1019 y
116Cd T1/2 = 2.8 ± 0.1 (stat) ± 0.3 (syst)  1019 y
150Nd T1/2 = 9.7 ± 0.7 (stat) ± 1.0 (syst)  1018 y
96Zr T1/2 = 2.0 ± 0.3 (stat) ± 0.2 (syst)  1019 y
48Ca T1/2 = 3.9 ± 0.7 (stat) ± 0.6 (syst)  1019 y
48Ca
background subtracted
M. Dracos, Osaka, 26/05/2010

20. Super NEMO R&D up to 2010/2011, construction
M. Dracos
Super NEMO
Improvements:
Energy resolution 15%  DE/E = 4% @ 3 MeV
Efficiency 15%  % @ 3 MeV
Source x10 larger 7kg  kg
Most promising isotopes
82Se (baseline) or perhaps
150Nd
Aim: T1/2 > 2 x 1026 y
  Mbb  < meV
R&D up to 2010/2011, construction
between 2012 and 2014 (if approved)
source sheet
M. Dracos, Osaka, 26/05/2010

21. Nuclear Emulsions Compact objects ("cheap" detectors)
M. Dracos
Nuclear Emulsions
Compact objects ("cheap" detectors)
Very high space accuracy (<mm)
3D information
No need for high tech, nor super trained staff
Very suitable for discoveries
1947 Lattes, Muirhead, Occhialini & Powell observe p→m→e in nuclear emulsions using cosmic rays (few events are significant to make a discovery)
1951
M. Dracos, Osaka, 26/05/2010

22. OPERA Experiment Nuclear Emulsions ~15 grains/50 mm τ nt nm
M. Dracos
OPERA Experiment
~15 grains/50 mm
emulsion “grains” 
track segment nt
ne , nm
High spatial resolution is needed
(do not forget that large surfaces have to be covered)
e, m, h τ nt nm
decay “kink”
>25 mrad
Nuclear Emulsions
sqx~ 2.1 mrad
sx~ 0.21 mm Pb ES Pb ES
(μm)
1 mm
M. Dracos, Osaka, 26/05/2010

23. The OPERA Detector n Target Tracker + brick walls (2x31)
"target" wall
(full description in JINST 4, P04018 (2009))
Pb/emulsion brick wall
scintillator strips n
brick
(56 Pb/Em.)
Target Tracker
+ brick walls
(2x31)
8 cm (10X0)
bricks
(1.25 kt)
robot
muon spectrometer
(RPC + drift tubes)
8.3 Kg
M. Dracos, TAUP09
Changeable Sheet Doublet
M. Dracos

24. The BMS (Brick Manipulator System) BAM (Brick Assembling Machine)
The OPERA Detector
"Industrial" production, development, handling, scanning and analysis of emulsions.
The BMS (Brick Manipulator System)
BAM (Brick Assembling Machine)
5 articulated robots
M. Dracos, TAUP09
M. Dracos

25. The OPERA emulsion scanning
Based on the tomographic acquisition of emulsion layers.
Nominal scanning speed ~20 cm2/h.
~ 20 bricks daily extracted → thousands of cm2/day
The European Scanning System
The S-UTS (Japan)
Customized commercial optics and mechanics
Hard coded algorithms (speed higher than 50 cm2/h)
M. Dracos, TAUP09
M. Dracos

26. The OPERA first event   W hadrons Muon momentum: ~7.5 GeV
charged current
Muon momentum: ~7.5 GeV
M. Dracos, TAUP09
M. Dracos

27. b decay with emulsions
M. Dracos
b decay with emulsions
"veto" emulsion,
if needed
(~50 m like in OPERA?) e e
beta source
(~50 m in NEMO3
could be less for emulsions)
plastic base
"b" emulsion
thick enough to detect up to 4 MeV electrons (density?)
J. Soc. Photogr. Sci. Technol. Japan. (2008) Vol. 71 No. 5 (
Radiation Measurements 44 (2009) 729–732
M. Dracos, Osaka, 26/05/2010

28. Tests in Nagoya using OPERA nuclear emulsions
M. Dracos
Tests in Nagoya using OPERA nuclear emulsions
A. Ariga, diploma thesis
electron spectrometer
50 m
M. Dracos, Osaka, 26/05/2010

29. Electron tracks in emulsions
M. Dracos
Electron tracks in emulsions
1 MeV e-
simulation
100 m
simulation
2 MeV e-
(A. Ariga and NIM A 575 (2007) 466)
M. Dracos, Osaka, 26/05/2010

30. b decay with emulsions (comparison with NEMO3/SNEMO)
M. Dracos
b decay with emulsions (comparison with NEMO3/SNEMO)
NEMO3 surface: 20 m2
Super-NEMO surface: 10x20 m2
To cover the same isotope source surface with emulsions (both sides to detect the 2 electrons) we need an emulsion surface: 2x200=400 m2.
Just for comparison, one OPERA emulsion has a surface of about m2 and one brick 0.680 m2. So 400 m2 is about the equivalent of 600 OPERA bricks over (but not with the same thickness of course, taking into account the thickness this could be the equivalent in emulsion volume of about OPERA bricks).
Use the same envelops like the OPERA changeable sheets by introducing at the middle of the two emulsions (or stack of emulsion sheets) a double beta source sheet.
Keep all these envelops for some time (e.g months) in the experiment and after this period start scanning them one after the other. They could be replaced by new envelops during 5 years in order to accumulate something equivalent to what Super-NEMO could do: 5*400 year*m2
Experiment volume: <5 m3  very compact experiment!
M. Dracos, Osaka, 26/05/2010

31. Previous tentative Conclusion: 1.28 g 96Zr (powder)
M. Dracos
Previous tentative
1.28 g 96Zr (powder)
source thickness: 180 m
total exposure time: 3717 hours
scanned surface for electron pairs: 10 mm2
estimated total efficiency: 18%
Conclusion:
T1/2(96Zr)>1017 years,
decrease the thickness of the isotope layer,
use low radioactivity emulsions,
scanning speed has to considerably be increased (automatic scanning needed).
M. Dracos, Osaka, 26/05/2010

32. M. Dracos
Emulsion scanning
How much time is needed to make a full scan of 2000 m2 (full scan in all volume not needed, just follow tracks present in the emulsion layer near the isotope foil)?
If the Japanese S-UTS scanning system is used with a speed of 50 cm2/hour, for one scanning table: 25 m2/year (200 working days/year). By using 16 tables and extracting 100 m2/3 months (1 year exposure at the beginning and putting back new emulsions with the same isotopes), this finally will take less than 5 years (as Super-NEMO).
Probably the emulsion thickness needed to detect these electrons will need more scanning time and the speed would be significantly less than 50 cm2/h. On the other hand, scanning speed increases with time…
0.003
0.1
1.2
7.0 40 60
140
700
0.001
0.01 1 10
100
1000 cm 2
/ h
TS(1994)
NTS(1996)
UTS(1998)
SUTS(2006)
SUTS(2007-)
Scanning Power Roadmap
1stage
facility
CHORUS
DONUT
OPERA
Nakamura san
Nufact07
M. Dracos, Osaka, 26/05/2010

33. Pending questions Energy resolution for NEMO: 15% for 1 MeV electrons
M. Dracos
Pending questions
Energy resolution for NEMO: 15% for 1 MeV electrons
Required for Super-NEMO: lower than 8%
Emulsion experiment energy resolution: ???
Overall reconstruction efficiency for NEMO: 15-18%
Required for Super-NEMO: >30%
Emulsion experiment reconstruction efficiency: ?
Minimum electron energy (~0.5 MeV?, MeV for NEMO3), will greatly influence the total efficiency.
Afforded background (fog)??
Possibility to take thinner isotope sheets (60 m for NEMO3) and have better energy resolution (but also more scanning for the same isotope mass, find good compromise).
M. Dracos, Osaka, 26/05/2010

34. Possible isotopes to be used
M. Dracos
Possible isotopes to be used
For emulsions the electron detection threshold cannot be so low than NEMO3 (200 keV, low density material gas+plastic scintillator)  utilisation of high Q-value isotopes>3 MeV
advantage: low background, high efficiency
problem: low abundance
M. Dracos, Osaka, 26/05/2010

35. Low energy cut and efficiency
M. Dracos
Low energy cut and efficiency
The higher the Q-value the better the detection efficiency
For Ecut=0.5 MeV:
ECa~94%
ENd~86%
EMo~84%
From all detection points of view 48Ca is the best, but very low abundance…
light majorana neutrino model
0.5 MeV seams a reachable limit, is it possible to go even lower?
M. Dracos, Osaka, 26/05/2010

36. Low energy cut and efficiency
M. Dracos
Low energy cut and efficiency
For this model the efficiency will be lower than the previous one
For Ecut=0.5 MeV:
Eca~72 (94) %
ENd~54 (86)%
EMo~50 (84)%
right handed current model
(heavy majorana neutrino)
M. Dracos, Osaka, 26/05/2010

37. Thick Emulsions are needed
M. Dracos
Thick Emulsions are needed
To stop up to 48Ca isotope electrons ~5 mm thick emulsions are needed,
A stack of 10 emulsion layers 0.5 mm thick could be used.
M. Dracos, Osaka, 26/05/2010

38. Feasibility studies 207Bi source with well known activity
M. Dracos
Feasibility studies
207Bi source with well known activity
(EICe-=976, 482 keV)
emulsion sheets 0.6 mm thick
(3-4 layers)
Reconstruction efficiency: by counting the number of reconstructed electrons from both energy lines after scanning (this would also help to tune the algorithms).
Electron threshold: the reconstruction efficiency for both electrons (mainly those at 482 keV) would give a good idea about the threshold.
Energy resolution: by counting the associated grains to the track, by measuring the track range.
Afforded background: perform the above tests with different backgrounds.
Needed
scanning tables,
low radioactivity lab (Gran Sasso, Baksan, Fréjus…),
thick emulsions (provided by Fuji?)
M. Dracos, Osaka, 26/05/2010

39. Limitations high multiple scattering for low energy electrons
M. Dracos
Limitations
high multiple scattering for low energy electrons
de/dx fluctuations
bremsstrahlung gammas (energy lost)
lost -electrons
electron backscattering
0.7 MeV e-
(10 tracks)
d=2.7 g/cm3
(Geant 3.2)
better to use low density emulsions?
(by chance OPERA emulsions could be the best)
M. Dracos, Osaka, 26/05/2010

40. M. Dracos
Extra Ideas e
decreasing density
(25 m layers)
to minimize the emulsion thickness and better energy resolution at the end of the track e
emitter in powder (diluted in an emulsion layer ~25 mm)
better vertex and energy reconstruction?
(few isotopes are anyway in powder form)
M. Dracos, Osaka, 26/05/2010

41. M. Dracos
Extra Ideas
top
Tests of dilution of Mo powder into 75 mm nuclear emulsion
high size granules go down during the emulsion production, but this is not a problem,
the optical properties are not affected,
the maximum afforded Mo density has been determined (keeping high detection efficiency). e
bottom (
M. Dracos, Osaka, 26/05/2010

42. M. Dracos
BACKGROUND EVENTS OBSERVED BY NEMO-3 which could be easily rejected in emulsions
Electron crossing > 4 MeV Neutron capture
Electron + a delay track (164 ms) 214Bi  214Po  210Pb
end of tracks easily recognised in emulsions  rejection
alpha tracks easily recognised in emulsions  rejection
M. Dracos, Osaka, 26/05/2010

43. BACKGROUND EVENTS OBSERVED BY NEMO-3 and rejection in emulsions
M. Dracos
BACKGROUND EVENTS OBSERVED BY NEMO-3 and rejection in emulsions 
Electron + N g’s 208Tl (Eg = 2.6 MeV)
Electron – positron pair B rejection
cannot be rejected in absence of magnetic field  good emulsion shielding
no vertex or very good vertex resolution in emulsions  rejection
M. Dracos, Osaka, 26/05/2010

44. NEMO3 main background configurations
M. Dracos
NEMO3 main background configurations
Proportion of types of events in raw data:
Type of event
Rate (mHz)
1 e-, 0g
600
1 e-, Ng (N1)
150
e+e- pairs
110
Crossing e- 80
bb event
5.4 mHz
M. Dracos, Osaka, 26/05/2010

45. Tadaaki Tani (Frontier Res. Labs, FUJIFILM)
M. Dracos
Emulsion R&D
done by Fuji
R&D to remove 40K from gelatine to decrease the fog → very promising results
Tadaaki Tani (Frontier Res. Labs, FUJIFILM)
M. Dracos, Osaka, 26/05/2010

46. M. Dracos
Conclusion
Technology allows today the investigation about observation of neutrinoless double beta decays using nuclear emulsions, advantages of the method:
tracking and calorimetry,
very high resolution detector,
very compact volume easily shielded against external radioactivity,
flexibility to change isotopes at any time,
no fluids,
cost effective technique (easy to operate).
To prove the experiment feasibility few questions have to be answered:
what is the energy resolution?
what is the afforded background?
what is the overall efficiency?
The above questions could be answered with relatively low investment.
M. Dracos, Osaka, 26/05/2010

47. Thank you for your kind attention
M. Dracos
END
Thank you for your kind attention
M. Dracos, Osaka, 26/05/2010