1. Neutrino Ettore Majorana Observatory
NEMO Experiment
Neutrino Ettore Majorana Observatory
Xavier Sarazin 1
On behalf of the
NEMO Collaboration
CENBG, IN2P3-CNRS et Université de Bordeaux, France
Charles University, Praha, Czech Republic
CTU, Praha, Czech Republic
INEEL, Idaho Falls, USA
IReS, IN2P3-CNRS et Université de Strasbourg, France
ITEP, Moscou, Russia
JINR, Dubna, Russia
Jyvaskyla University, Finland
1 LAL, IN2P3-CNRS et Université Paris-Sud, France
LSCE, CNRS Gif sur Yvette, France
LPC, IN2P3-CNRS et Université de Caen, France
Mount Holyoke College, USA
RRC Kurchatov Institute, Moscow, Russia
Saga University, Saga, Japon
UCL, London, Great-Britain
Xavier Sarazin for the NEMO-3 Collaboration TPC Workshop December 2004

2. Double beta bb(0n) decay : Physics beyond the standard model
DL = 2 Process
Majorana Neutrino n = n and effective mass <mn>
Right-handed current in weak interaction
Majoron emission
SUSY particle exchange
bb(0n) : 2n  2p+2e- p n W- e-
neR h nM
neL h
( ) e- W- n p
(Qbb ~ MeV)

3. Philosophy of NEMO experiment
Use a Tracking Detector + a Magnetic Field
in order to recognize e-, e+, g and a particles
Zero-background experiment
Gold-event experiment
with a direct signature of the two emitted e-

4. 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 + Boron (ext. wall); 40 cm wood (top and bottom)
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: FWHM ~ 1 MeV
1940 plastic scintillators
coupled to low radioactivity PMTs
ToF resolution MeV
Able to identify e-, e+, g and a

5. PMTs scintillators Cathodic rings Wire chamber Calibration tube
bb isotope foils

6. AUGUST 2001

7. Start taking data 14 February 2003
NEMO-3 Opening Day, July 2002
Start taking data 14 February 2003
Water tank
wood
coil
Iron shield

8. bb decay isotopes in NEMO-3 detector
bb2n measurement
116Cd g
Qbb = keV
96Zr g
Qbb = 3350 keV
150Nd g
Qbb = keV
48Ca g
Qbb = 4272 keV
130Te g
Qbb = 2529 keV
External bkg
measurement
100Mo kg
Qbb = 3034 keV
82Se kg
Qbb = 2995 keV
natTe g
Cu g
bb0n search
(All the enriched isotopes produced in Russia)

9. 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
bb events: 1 event every 1.5 minutes

10. 100Mo 22 preliminary results
Neutrino 2004
100Mo 22 preliminary results
(Data 14 Feb – 22 Mar. 2004)
Sum Energy Spectrum
Angular Distribution
NEMO-3
events
6914 g
241.5 days
S/B = 45.8
NEMO-3
events
6914 g
241.5 days
S/B = 45.8
100Mo
100Mo
Data
22
Monte Carlo
Data
Background
subtracted
22
Monte Carlo
Background
subtracted
E1 + E2 (keV)
Cos()
T1/2 = 7.72 ± 0.02 (stat) ± 0.54 (syst)  1018 y
4.57 kg.y

11. NEMO can measure each component of background
Radon
Internal 214Bi impurities
(e-, delayed a) channel with T1/2 (a) = 164 ms
(214Bi - 214Po -210Pb )
Internal 208Tl impurities
Internal (e- N g) channel with Eg= 2.6 MeV
(e-, delayed a) channel with T1/2(a)=300 ns
(212Bi  212Po)
External 208Tl impurities
External (e-, g) channel
External neutrons External gammas
e- crossing, e+e-, e-e- > 4 MeV

12. BACKGROUND EVENTS OBSERVED BY NEMO-3…
Electron crossing > 4 MeV Neutron capture
Electron + a delay track (164 ms) 214Bi  214Po  210Pb 
Electron + N g’s 208Tl (Eg = 2.6 MeV)
Electron – positron pair B rejection

13. Radon was the dominant background
Radon in the NEMO-3 gas of the wire chamber
Due to a tiny diffusion of the radon of the laboratory inside the detector
A(Radon) in the lab ~15 Bq/m3
Two independant measurements of radon in NEMO-3 gas
Good agreement between the two measurements
Radon detector at the input/output of the NEMO-3 gas
~ 20 counts/day for 20 mBq/ m3
(1e- + 1 a) channel in the NEMO-3 data:
Delayed tracks (<700 ms) to tag delayed a from 214Po
214Bi  214Po (164 ms)  210Pb
~ 200 counts/hour for 20 mBq/m3
A(Radon) in NEMO-3  20 mBq/m3
Decay
in gas b-
delayed a
222Rn (3.8 days)
218Po
214Pb
214Bi
214Po
210Pb b a
164 ms
~ 1 bb0n-like events/year/kg with 2.8 < E1+E2 < 3.2 MeV
Radon was the dominant background
for bb0n search in NEMO-3 !!!

14. bb0n Analysis with 100Mo T1/2(bb0n) > 3.5 1023 y 90% C.L.
Neutrino 2004
100Mo
6914 g
265 days
Data
bb2n
Monte-Carlo
Radon
E1+E2 (MeV)
bb0n arbitrary
unit
Cu + natTe + 130Te
265 days
Radon
Monte-Carlo
Data
E1+E2 (MeV) 8
11.4  3.4
____
2.6  0.7 2
2.6<E1+E2<3.2
2.8<E1+E2<3.2
100Mo
2.6<E1+E2<3.2
2.8<E1+E2<3.2
100Mo 2b2n M-C
32.3  1.9
1.4  0.2
Radon M-C
23.5  6.7
5.6  1.7
TOTAL Monte-Carlo
55.8  7.0
7.0  1.7
DATA 50 8
T1/2(bb0n) > y 90% C.L.
mn < 0.7 – 1.2 eV

15. Free-Radon Purification System
in construction
Radon was the dominant
background for NEMO-3
A(222Rn) in the LSM ~ 15 Bq/m3
Factor ~ 10 too high
May 2004 : Tent surrounding the detector
May 2004
October 2004 : Radon-free
SuperKamiokande-like
Air Factory
A(222Rn) < 10 mBq/m3
120 m3/h
2 x 500 kg -40oC
Today A(222Rn) in tent < 0.5 Bq/m3
Rejection Factor > 30

16. Expected sensitivity after 5 years of data
Conclusions after more than 1 year of NEMO-3 running
NEMO detector is robust
NEMO can measure each component of its background
External 208Tl: external (e-,g) channel
External neutrons and g: crossing e- above 4 MeV
Internal 208Tl impurities: internal (e-,Ng) channel, A<100 mBq/kg
Internal 214Bi impurities and Radon: (e-,delayed a) channel from Bi-Po process
Radon was the dominant background
supressed by radon-free air surrounding the detector
Very low levels of background have be achieved with ~ 10 kg of isotopes
Expected sensitivity after 5 years of data
(with FWHM ~ 1 MeV)
with 7 kg of 100Mo: T1/2(bb0n) > y  <mn> < 0.2 – 0.35 eV (90% C.L.)
with 1 kg of 82Se: T1/2(bb0n) > y  <mn> < – 1.8 eV (90% C.L.)

17. Can we increase the mass of isotope
Question :
Can we increase the mass of isotope
with such a detector ?

18. SuperNEMO: a futur detector with ~100 kg of 82Se
Zero background experiment with a direct signature of the two emitted e-
 To reach a sensitivity ~ 50 meV
bb(0n) ?
Klapdor et al. Phys. Lett. B 586(2004),
Test Klapdor’s claim
T 1/2 (0n) = ( ) 1025 y (90% C.L.)
0.1 eV < mn < 0.9 eV
NEMO-3
Access to inverted hierarchical mass spectrum
SuperNEMO

19. 2b2n bkg with 100 kg of 82Se  2b2n bkg with 7 kg of 100Mo
T1/2 (2b2n) = years for 100Mo
= 1020 years for 82Se
2b2n bkg with 100 kg of 82Se  2b2n bkg with 7 kg of 100Mo
> e A
M . t
Nexcluded
ln2 . N
(years)
M: Mass of isotope bb (g)
e: Detection efficiency
With e ~ 0.2 (as NEMO-3)
M = 100 kg of 82Se
« Zero Background »  Energy resolution FWHM < 1 MeV
5 years of data: T1/2 (0n) > y  mn < 40 – 100 meV
10 years of data: T1/2 (0n) > y  mn < 30 – 70 meV

20. Example of a module of SuperNEMO: « extrapolation of NEMO-2-3 »
Module 4 x 4 x 1 m3
Source 3 x 3 m2 ~ 5 kg of 82Se
1000 scintillator blocs (20 x 20 x 10) cm + PMTs 8’’
4 m
1 m
4 m
3 m
3 m
4 m

21. etc… Example of a SuperNEMO = 20 modules with water shield
~ 9 m large,
~ 12 m high to remove a module…
~ 70 m long !…
~ 1.5 m
~ 5 m
etc…
Water shield
Coil for Magnetic field

22. Program R&D during 2 years
Calorimeter
FWHM = 7 % scintillator + PMT
Collaboration France (CENBG), Dubna, Kharkov, UCL and Photonis
Light collection to decrease number of PMT
separate e- calorimeter (thin scintillator) and g tagging (larger scinttilator)
Source
R&D purification 82Se in INEEL (USA)
208Tl ~5mBq/kg and 214Bi 20 mBq/kg (factor 10 / NEMO3)
Production of 2 kg of 82Se with ILIAS (Russia)
Active sources 20 mm (LAL, Russia, INEEL) e- e-
Tracking
Full plasma propagation with Geiger cells of 4 m long (LAL)
reduce Diameter /or mass of wires
a/e- tagging beetween active sources e- e-
Simulations (IRES, LPC Caen)
Geometry
Shielding …
Active source
Proposal for R&D and first module in preparation with british collaborators

23. CONCLUSIONS Almost 2 years of NEMO-3 running have demonstrated that
NEMO detector is robust
Detector can measure each component of background
origines of background are understood
very low backgrounds have been achieved (as the proposal)
Possible to extrapolate such a detector to a SuperNEMO detector
with ~100 kg of 82Se to reach ~ 50 meV
Pragmatic experimental approche
Proposal for 2 years of R&D and construction of a 1st module is under preparation