Double Beta experiment with emulsions?

1
Double Beta experiment with emulsions?
2
Double Beta Decay
allowed double beta
double beta without neutrino
T 1/2 1019-1020 years !
Observed for Mo100, Ge76, Se82, Cd116, Te130,
Zr96, Ca48, Nd150
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
The NEMO3 experiment
3
The NEMO3 detector
expected sensitivity up to mn0.3 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
4
Event Examples
5
Results
932 g 389 days 2750 even. S/B 4
T1/2(bb0n) gt 5.8 1023 (90 C.L.) ? ltmngt lt0.6-2.5
eV
100Mo ( 7 kg )
Expected in 2009 T1/2(bb0n) gt 2 1024 (90
C.L.) ? ltmngt lt0.3-1.3 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
background subtracted
6
Super NEMO

• Improvements
• Energy resolution 15 ? DE/E 4 _at_ 3 MeV
• Efficiency 15 ? 20 - 40 _at_ 3 MeV
• Source x10 larger 7kg ? 100 - 200 kg
• Most promising isotopes
• 82Se (baseline) or perhaps
• 150Nd
• Aim T1/2 gt 2 x 1026 y
• ? ? Mbb ? lt 40 - 90 meV
• RD up to 2009, construction
• between 2010 and 2013

source sheet
7
2? with emulsions
"veto" emulsion, if needed (50 ?m like in OPERA?)
beta source (50 ?m inNEMO could be less for
emulsions)
plastic base
"2?" emulsion thick enough to detect up to 4 MeV
electrons (density?)
8
Tests in Nagoya using OPERA emulsions
A. Ariga, diploma thesis
50 ?m
9
2? with emulsions
simulation
simulation
10
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 2x200400 m2.
• Just for comparison, one OPERA emulsion has about
  0.012 m2 and one brick 0.680 m2. So 400 m2 is
  about the equivalent of 600 OPERA bricks over
  150000 (but not with the same thickness of
  course).
• Use the same envelops like the OPERA changeable
  sheets by introducing at the middle of the two
  emulsions a double beta source sheet, or use
  longer emulsion sheets easier to handle by
  microscopes.
• Keep all these envelops for some time (e.g. 6-12
  months depending on fading) 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 ?4005
  yearm2

11
2? with emulsions

• How much time is needed to make a full scan of
  2000 m2 (is a full scan in all volume really
  needed?)?
• If the Japanese S-UTS scanning system is used
  with a speed of 50 cm2/hour (be careful with
  thickness), 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

Nakamura san Nufact07
12
Pending questions

• Energy resolution for NEMO 15 for 3 MeV
  electrons
• Required for Super-NEMO lower than 7 (goal 4)
• Emulsion experiment energy resolution ???
  (monoenergetic 1 MeV 207Bi electrons could be
  used to have a good estimate of this resolution)
• Reconstruction efficiency for NEMO 15
• Required for Super-NEMO 40
• Emulsion experiment reconstruction efficiency ??
  (here also a well calibrated 207Bi source or
  other sources could be used)
• Minimum electron energy (1 MeV, 0.5 MeV for
  NEMO3?)
• Afforded background?
• Could magnetic field help (better momentum
  resolution or ? rejection)?
• Possibility to take thinner isotope sheets (60 ?m
  for NEMO3) and have better energy resolution (but
  also more scanning for the same isotope mass).

13
Extra Ideas
after discussion with Fuji engineers, all these
ideas are possible!
e
e
e
e
decreasing density (25 mm layers)
emitter in powder (diluted in an emulsion layer)
to minimize the emulsion thickness and better
energy resolution at the end of the track
better vertex and energy reconstruction ?
14
END
15
2? with emulsions
for 400  m2/year and 400 m2 isotopes available
isotope block number time (years) surface (m2) exposure time (years) surfacetime (m2years)
1 1.00 100 1.00 100
2 1.25 100 1.25 125
3 1.50 100 1.50 150
4 1.75 100 1.75 175
1 2.00 100 1.00 100
2 2.25 100 1.00 100
3 2.50 100 1.00 100
4 2.75 100 1.00 100
1 3.00 100 1.00 100
2 3.25 100 1.00 100
3 3.50 100 1.00 100
4 3.75 100 1.00 100
total 3.75 1200 13.50 1350
16
BACKGROUND EVENTS OBSERVED BY NEMO-3
Electron a delay track (164 ms) 214Bi ? 214Po
? 210Pb
Electron crossing gt 4 MeV Neutron capture
?
Electron positron pair B rejection
Electron N gs 208Tl (Eg 2.6 MeV)
17
bb0n-like event due to Radon from the gas (NEMO3)
a track (delay 70 ms) 214Po ? 210Pb

• 214Bi ? 214Po
• decay
• IN THE GAS

18
NEMO3
Proportion of types of events in raw data
Type of event Rate (mHz)
1 e-, 0g 600
1 e-, Ng (N?1) 150
ee- pairs 110
Crossing e- 80
bb event 5.4 mHz