1. Search for 0nbb decay with SuperNEMO
Ruben Saakyan
UCL
UCL_HEP/MSSL day out
18 July 2005

2. Outline
Neutrinos
0nbb decay
NEMO-III
SuperNEMO

3. Why study neutrinos?
2nd most abundant particle in the Universe photons ~ 107/m neutrinos ~ 3  106/m protons ~ 0.5/m3
As many produced in Big Bang as photons. Crucial for element formation.
Only 1% of energy from supernova appears as photons. Other 99% is neutrinos.
Neutrinos are crucial for our understanding how the Sun shines.
Very important for heavy element formation in stars (CNO cycle).
Neutrino astronomy: the only way to study distant objects
Very far-future neutrino beams: search for oil and destroy WMD?

4. Why study neutrinos?
Essential part of the building blocks of matter and the Universe
Fundamental for understanding deep principles of nature
In Standard Model assumed to be massless
We now know they have non-zero mass
Neutrino mass – window beyond Standard Model

9. Absolute neutrino mass
Neutrino oscillations measure Dm2  can not solve this problem
For sure less than g
3H decay (look at end point of b-spectrum)
Cosmology
0nbb decay

10. Weighing neutrino. Cosmology.
mi < 0.7 – 2.2 eV

11. Double beta decay and neutrino mass
Neutrino nature  Dirac (n  (anti)n vs Majorana (n = (anti)n)
The only way to answer this fundamental question
Absolute neutrino mass
Might be the only way to weigh n in a lab
Important consequences for particle physics, cosmology, nuclear physics

12. Double beta decay and neutrino mass
DL=0
DL=2 !
Q

14. A controversial claim by Heidelberg-Moscow group (4.2s)
214Bi
unknown
214Bi
0nbb
71.7 kgyr
A controversial claim by Heidelberg-Moscow group (4.2s)

15. NEMO-3
AUGUST 2001

16. Fréjus Underground Laboratory : 4800 m.w.e.
The NEMO3 detector
3 m
4 m
B (25 G)
20 sectors
Fréjus Underground Laboratory : 4800 m.w.e.
Magnetic field: 25 Gauss
Gamma shield: Pure Iron (e = 18 cm)
Neutron shield: 30 cm water (ext. wall)
40 cm wood (top and bottom)
(since march 2004: water + boron)
Source: 10 kg of  isotopes
cylindrical, S = 20 m2, e ~ 60 mg/cm2
Tracking detector:
drift wire chamber operating
in Geiger mode (6180 cells)
Gas: He + 4% ethyl alcohol + 1% Ar + 0.1% H2O
Calorimeter:
1940 plastic scintillators
coupled to low radioactivity PMTs
Able to identify e-, e+, g and a

17. PMTs scintillators Cathode rings Wire chamber Calibration tube
bb isotope foils

18. Sensitivity to mn ~ 0.2 – 0.4 eV by 2009
bb decay isotopes in NEMO-3 detector
bb2n measurement
116Cd g
Qbb = keV
96Zr g
Qbb = 3350 keV
Sensitivity to mn ~ 0.2 – 0.4 eV by 2009
150Nd g
Qbb = keV
48Ca g
Qbb = 4272 keV
130Te g
Qbb = 2529 keV
82Se kg
Qbb = 2995 keV
External bkg
measurement
natTe g
100Mo kg
Qbb = 3034 keV
Cu g
bb0n search
(All enriched isotopes produced in Russia)

19. bb events selection in NEMO-3
Deposited energy:
E1+E2= 2088 keV
Internal hypothesis:
(Dt)mes –(Dt)theo = 0.22 ns
Common vertex:
(Dvertex) = 2.1 mm
Vertex
emission
(Dvertex)// = 5.7 mm
Transverse view
Longitudinal
view
Run Number: 2040
Event Number: 9732
Date:
Criteria to select bb events:
2 tracks with charge < 0
2 PMT, each > 200 keV
PMT-Track association
Common vertex
Internal hypothesis (external event rejection)
No other isolated PMT (g rejection)
No delayed track (214Bi rejection)
bb events selection in NEMO-3
Typical bb2n event observed from 100Mo
Transverse view
Run Number: 2040
Event Number: 9732
Date:
Longitudinal
view
100Mo foil
100Mo foil
Geiger plasma
longitudinal
propagation
Drift distance
Scintillator
+ PMT
Trigger: PMT > 150 keV
3 Geiger hits (2 neighbour layers + 1)
Trigger rate = 7 Hz

20. From NEMO-III to SuperNEMO. Motivation.
Very successful technology. > 15 years of experience.
Quick start as a lengthy R&D is not needed
Next generation bb0n experiments should have at least one “bubble chamber”-like detector which will see a signature of bb events

21. SuperNEMO = NEMO3×10(20) + better DE/E
Sensitivity ~0.03 – 0.06 eV in 5 yr
Feasible if Zero BG experiment:
1) No BG from radioactivity
the only possible BG from
2n tail (NEMO-III)
2) Improve DE/E from
existing (14%-16%)/E to
(7%-9%)/E*
*Demonstrated (UCL+ Bordeaux)
DE/E = 8% at 1 MeV
DE/E = 12% at 1 MeV

22. SuperNEMO. Possible Sites.
Frejus – France (new cavern)
Boulby – UK
Gran Sasso – Italy
Canfranc – Spain

23. 10-20,000 PMts/scintillator blocks
Baseline conceptual design. Scintillator blocks
SuperNEMO = submodule × 50
100 kg of 82Se (or other) in
2m×4m×40m +
shielding
10-20,000 PMts/scintillator blocks

24. Possible alternative scintillator bar design
Double sided readout
If feasible can reduce the number
of PMT’s to 3-5,000 as well as
the floor area to ~12x12 m2

25. UK involvement
The UK group is part of the international Super-NEMO collaboration (UCL/MSSL, Manchester)
This proposal is part of a coordinated approach with the French to start Super-NEMO
UK/French groups have agreed on the sharing of the main work.
Other collaborators (Russia, Czech Rep, Japan, US will contribute on a smaller scale)
Money request for a 2 yr design study submitted by UK (PPRP), France (IN2P3), US (NUSAG).
UK main contributions:
Tracking detector
Finish up ongoing scinitllator R&D

26. MSSL involvement
Large scale production  exploit MSSL technical expertise
New Lab space allows UK to bid for such big construction projects
MSSL main contributions
Tracking detector R&D + Wiring robot
SuperNEMO submodule production

27. Wiring robot The challenge: from 6,000 to ~60,000+ cells Wires must be
strung
terminated
crimped
This can not be done
manually (~10 min/wire)
Complications
Copper pick-ups
Must be cost effective
Solder can not be used (radiopurity)

28. Tracker Read-out Electronics
Prompt signal from anode
wires (transverse coordinate)
Delayed signal from cathode
rings (longitudinal coordinate
TDC read-out with ~20 ns
resolution
Triggering based on track
parameters
Custom discriminator chip on or close to detector
Challenges:
Large number of channels (~60,000+)
High radiopurity

29. Tracker Front-End ASIC (Application Specific Integrated Circuits)
Design and prototype at UCL/MSSL
Amplifiers and discriminators with programmable threshould and zero suppression
Data collection and triggering/buffering/clock via serial link to minimise number of connections
Exact ASIC specifications need to be developed

30. Tracker Read-Out Boards
Design and prototype in close collaboration with UCL and Manchester HEP
Concentrator boards receive data from ASIC
provide data reduction and concentration
provide trigger data and first stage track reconstruction
Final read-out/track reconstruction/on-line monitoring via a DAQ PC farm.
FPGAs can be used to model ASIC for prototyping

31. SuperNEMO Milestones.
2004 – 2005: ongoing scintillator R&D in UK, France, Russia, US
March Design study proposal submitted to UK and French funding agencies. UK answer after 24th August
By mid 2007
Full Technical Design
Prototype
Experimental site
2007: Full Proposal
2007 – 2010: Production
: Start taking data
2014: planned sensitivity ~0.04 eV

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 experiments in the £25M range: this is more than reasonable for the potential scientific gain
SuperNEMO is so far the only project which will look at 0nbb signature
Thanks to MSSL facilities UK (and specifically UCL) can be a crucial player in these and other large HEP projects