1. Double Beta experiment using nuclear emulsions?
M. Dracos
Double Beta experiment using nuclear emulsions?
Marcos Dracos
IPHC/IN2P3, Strasbourg
M. Dracos, Bologna, 01/09/2008

2. Double Beta Decay ? L=2 T 1/2 ~ 1019-1020 years !
M. Dracos
Double Beta Decay
double beta without neutrino
L=2
allowed double beta
T 1/2 ~ years !
Observed for: Mo100, Ge76, Se82, Cd116, Te130, Zr96, Ca48, Nd150 ?
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.eia1 + m3|Ue3|2.eia2
|Uei|: mixing matrix elements, a1 and a2: Majorana phases 5
M. Dracos, Bologna, 01/09/2008

3. 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 ?
Degenerate
Goal of next
generation
experiments:
~10 meV
Inverted hierarchy
Lower bounds!
Normal hierarchy
| mee| in eV
M. Dracos, Bologna, 01/09/2008
Lightest neutrino (m1) in eV

4. 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, Bologna, 01/09/2008

5. 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, Bologna, 01/09/2008

6. plastic scintillator blocks
M. Dracos
The NEMO3 detector
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
M. Dracos, Bologna, 01/09/2008

7. M. Dracos
Event Examples
M. Dracos, Bologna, 01/09/2008

8. 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, Bologna, 01/09/2008

9. Super NEMO R&D up to 2009, 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 2009, construction
between 2010 and 2013 (if approved)
source sheet
M. Dracos, Bologna, 01/09/2008

10. 2 with emulsions e e "veto" emulsion, if needed
M. Dracos
2 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
"2" emulsion
thick enough to detect up to 4 MeV electrons (density?)
M. Dracos, Bologna, 01/09/2008

11. Tests in Nagoya using OPERA emulsions
M. Dracos
A. Ariga, diploma thesis
electron spectrometer
50 m
M. Dracos, Bologna, 01/09/2008

12. 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, Bologna, 01/09/2008

13. 2 with emulsions NEMO3 surface: 20 m2 Super-NEMO surface: 10x20 m2
M. Dracos
2 with emulsions
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, Bologna, 01/09/2008

14. 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, Bologna, 01/09/2008

15. 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, Bologna, 01/09/2008

16. 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?
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, Bologna, 01/09/2008

17. 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, Bologna, 01/09/2008

18. 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 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 (refreshed in low radioactivity lab).
M. Dracos, Bologna, 01/09/2008

19. 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?
M. Dracos, Bologna, 01/09/2008

20. Extra Ideas e e e e emitter in powder (diluted in an emulsion layer)
M. Dracos
Extra Ideas e e e e
emitter in powder (diluted in an emulsion layer)
decreasing density
(25 m layers)
better vertex and energy reconstruction?
(few isotopes are anyway in powder form)
to minimize the emulsion thickness and better energy resolution at the end of the track
M. Dracos, Bologna, 01/09/2008

21. BACKGROUND EVENTS OBSERVED BY NEMO-3 and rejection in emulsions
M. Dracos
BACKGROUND EVENTS OBSERVED BY NEMO-3 and rejection in emulsions
end of tracks easily recognised in emulsions  rejection
alpha tracks easily recognised in emulsions  rejection
Electron crossing > 4 MeV Neutron capture
Electron + a delay track (164 ms) 214Bi  214Po  210Pb
cannot be rejected in absence of magnetic field  good emulsion shielding
no vertex or very good vertex resolution in emulsions  rejection 
Electron + N g’s 208Tl (Eg = 2.6 MeV)
Electron – positron pair B rejection
M. Dracos, Bologna, 01/09/2008

22. bb0n-like event due to Radon from the gas (NEMO3)
M. Dracos
bb0n-like event due to Radon from the gas (NEMO3)
E1+E2= 2880 keV
a track
(delay = 70 ms)
214Po  210Pb
214Bi  214Po
decay
IN THE GAS
Run 2220, event , May 11th 2003
M. Dracos, Bologna, 01/09/2008

23. 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, Bologna, 01/09/2008

24. M. Dracos
Conclusion
Technology allows now the investigation about observation of double beta decays using nuclear emulsions
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, Bologna, 01/09/2008

25. M. Dracos
END
M. Dracos, Bologna, 01/09/2008