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Poszukiwanie
podwójnego bezneutrinowego
rozpadu beta w eksperymencie NEMO-3
Zenon Janas
Zakład Spektroskopii Jądrowej
IFD UW
Warszawa, 04.10.2006
Neutrino mixing
Maki-Nakagawa-Sakata-Pontecorvo (MNSP) matrix
U=
atmospheric
angle
sin223= 0.50±0.06
reactor angle
and CP phase
sin213< 0.012
solar angle
sin212= 0.31±0.03
Neutrino mass
tritium decay:
mb < 2.3 eV
cosmology:
m1+ m2 + m3 < 1.7 eV
oscillation exp.:
m22 – m12 = 7.9 ± 0.3 10-5 eV2
m32– m12 = 2.2 ± 0.4 10-3 eV2
Mass hierarchy
Normal
Inverted
Degnerate
?
m2
m12
m22
m32
Questions
• absolute mass scale ?
• mass hierarchy ?
• CP symmetry violation ?
• Dirac ( n  n ) or Majorana ( n  n ) particles ?
Double beta decay
(A, Z+1)
(A, Z)
bb
(A, Z+2)
bb decay modes:
 2nbb
(A, Z)  (A, Z+2) + 2 e + 2 ne
DL = 0
Feynman diagram for 2nbb decay
arbitrary units
Energy spectra of emitted electrons
(Qbb ~ MeV)
2nbb decay rate
T 
2n 1
1/ 2
 
G  Qbb
2v
M
2n 2
GT
11
G  M
2v
2n 2
GT
- phase space factor
- nuclear matrix element
Nuclear matrix element in 2nbb
1+
1+
GT
0+
1+
GT
(A, Z+1)
(A, Z)
0+
(A, Z+2)
2n
M GT


1
0f  1
1  0i
E (1 )  ( M i  M f ) / 2
J. Suhonen et al., Phys. Rep. 300 (1998) 123
Double beta decay
(A, Z+1)
(A, Z)
bb
(A, Z+2)
bb decay modes:
 2nbb
(A, Z)  (A, Z+2) + 2 e + 2 ne
DL = 0
 0nbb
(A, Z)  (A, Z+2) + 2e
DL = 2
Mechanisms of 0nbb decays
Light neutrino exchange
(V+A) current
Majoron emission
M
Energy spectra of electrons emitted in bb decay
M
0nbb decay rate
T 
0n 1
1/ 2
g A 0n
 G  M  M F  mbb
gV
0v
 
G  Qbb
2v
2
5
0n
MF0n , MGT
0n
GT
2
- phase space factor
- nuclear matrix elements
m bb
- effective Majorana mass


m bb  cos 2  13 m1 cos 2  12  m 2 e 2 i sin 2  12  m 3e 2 ib sin 2  13
Effective mass and neutrino mass scale
Inverse hierarchy
Normal hierarchy
Nuclear matrix elements in 0nbb
5+
21+
(A, Z+1)
0+
(A, Z)
0+
(A, Z+2)
M
0n
GT
 f

   
 l k l  k H (rlk , A ) i
l ,k
H (rlk , A) 
M F0n  f

 l k H (rlk , A ) i
l ,k
2R
r


dq
q sin(qr)
 (  A)
0
A  Em  ( Mi  M f )
- neutrino potential
Example
QRPA calculations for 100Mo
J
V.A. Rodin et al., nucl-th/0503063
Nuclear Matrix Elements calculations
Experimental approaches in bb decay studies
Calorimeter
Tracking + calorimeter
HPGe – Te bolometers
NEMO
only total energy measured
individual electrons observed
high energy resolution
modest energy resolution
good efficiency
small efficiency
compact detectors ( 10 m)
large detector size ( 50 m)
very pure crystals
background measured
source specific
universal
Both techniques are complementary !!
Heidelberg - Moscow experiment
11 kg 76Ge calorimeter, 71.7 kg·y exposure
214Bi
0n2b
T10/n2  0.7  4.2  1025 y (3 )
m bb  0.1  0.9 eV
H.V. Klapdor-Kleingrothaus et al., Phys. Lett. B586 (2004) 198
Neutrino Ettore Majorana Observatory
NEMO collaboration: 11 countries, 27 laboratories
USA
MHC
INL
U. Texas
Spain
U. Valencia
U. Zarogoza
U. Barcelona
Japan
U. Saga
KEK
U Osaka
Marocco
Fes U.
UK
UC London
U. Manchester
IC London
France
CEN Bordeaux
IReS Strasbourg
LAL ORSAY
LPC Caen
LSCE Gif/Yvette
Finland
U. Jyvaskyla
Russia
JINR Dubna
ITEP Mosow
Kurchatov Institute
Ukraine
INR Kiev
ISMA Kharkov
Slovakia
U. Bratislava
Czech
Charles U.
Praha
IEAP Praha
NEMO-3 detector
Location: Fréjus Underground Lab.
20 sectors
4800 m.w.e.
Source: 10 kg of bb isotopes
cylindrical, S = 20 m2, 60 mg/cm2
Tracking detector:
6180 drift wire chamber operating
in Geiger mode
3m
Gas: He + 4% ethyl alcohol + 1% Ar
Calorimeter:
1940 plastic scintillators
low radioactivity PMTs
B (25 G)
© S. Julian, LAL
NEMO-3 sector
PMT
Scint.
bb foil
R. Arnold et al., NIM A536 (2005) 79
NEMO-3 sector
cathodic rings
PMTs
Scint.
bb source
calibration
tube
bb sources in NEMO-3 detector
2nbb measurement
116Cd
405 g
Qbb = 2805 keV
96Zr
9.4 g
Qbb = 3350 keV
150Nd
37.0 g
Qbb = 3367 keV
48Ca
7.0 g
Qbb = 4272 keV
130Te
454 g
Qbb = 2529 keV
100Mo
6.914 kg
Qbb = 3034 keV
82Se
0.932 kg
Qbb = 2995 keV
0nbb search
natTe
491 g
Cu
621 g
background
measurement
NEMO-3 detector
Shielding of the NEMO detector
wood
(40 cm)
water+ B
(30 cm)
iron
(18 cm)
magnetic coil
(25 Gauss)
Performance of the NEMO-3
Tracking detector:
• vertex resolution:
 = 0.6 cm
// = 1.3 cm
• e+/e- separation with a magnetic field of 25 G
~ 3% confusion at 1 MeV
Calorimeter:
• energy resolution:
FWHM (1 MeV) = 14 – 17 %
• time resolution
FWHM (1 MeV)  250 ps
Typical 2nbb event from 100Mo isotope
Transverse view
Longitudinal
view
vertex
emission
vertex
emission
Deposited energy:
E1+E2= 2088 keV
Common vertex:
(Dvertex) = 2.1 mm
Trigger: at least 1 PMT > 150 keV
 3 Geiger hits (2 neighbour layers + 1)
Trigger rate = 5.8 Hz
bb events: 1 event every 2.5 minutes
(Dvertex)// = 5.7 mm
Background events in NEMO-3
Electron – positron pair

B rejection
Neutron capture
Electron crossing > 4 MeV
Background events in NEMO-3
238U
214Po
b
214Bi
(164 ms)
 7.7 MeV
0.021%
(19.9 mn)
210Pb
22.3 y
210Tl
(1.3 mn)
214Bi
 214Po  210Pb
electron +  delay (164 ms)
 208Pb
electron + 3 g’s
208Tl
Criteria to select bb events
• 2 tracks with charge < 0
• common vertex
• 2 PMT – associated with tacks
• no other isolated PMT ( g rejection )
• TOF condition (external event rejection)
• no delayed track (214Bi rejection)
2nbb decay of
100Mo
Sum Energy Spectrum
219 000 evnts
6914 g
389 days
2nbb sim.
bgnd
E1 + E2 (MeV)
2n
T1/2 = 7.1 ± 0.6  1018
y
0nM
T1/2 > 1.5  1022 y
Angular Distribution
219 000 evnts
6914 g
389 days
2nbb sim.
bgnd
cos(ee)
0nbb decay of 100Mo
0n2bb for
T1/2= 51022 y
0n
T1/2 > 4.6  1023 y
mbb < 0.7 – 2.8 eV
R. Arnold et al., PRL 95 (2005) 182302
2.8 - 3.2 MeV range
Nobserved = 7 events
bgnd
= 8.1 ± 1.3
bb decay of 82Se (Qbb=2995 keV)
2nbb
2nbb
82Se
2nbb sim.
bgnd
0n2bb for
T1/2= 51022 y
2n
T1/2 = 9.6 ± 1.3
y
 1019
R. Arnold et al., PRL 95 (2005) 182302
T1/2 > 1  1023 y
0n
mbb < 1.7 – 4.9 eV
Effective mass and neutrino mass scale
NEMO-3
Ge M-H
Inverse hierarchy
Normal hierarchy
2004 : tent surrounding the detector +
air purification system
Radon level 25 mBq/m3  3 mBq/m3
© S. Julian, LAL
From NEMO-3 to SuperNEMO
NEMO-3
SuperNEMO
100Mo
82Se
T1/2(bb2n) = 7 x 1018 y
7 kg
Isotope
Mass of isotope
e (bb0n) = 8 %
Efficiency
~ 11 % at 3 MeV
Resolution
~ 1 evt / 7 kg / y
T1/2(bb0n) > 2 x 1024 y
<mn> < 0.3 – 1.3 eV
208Tl
and 214Bi
background
SENSITIVITY
after 5 years
T1/2(bb2n) = 1020 y
100 kg
e (bb0n) ~ 30 %
~ 7 % at 3 MeV
~ 1 evt/ 100 kg / y
T1/2(bb0n) > 2 x 1026 y
<mn> < 0.04 – 0.1 eV
SuperNEMO - preliminary design
Plane geometry, 20 modules
1 module:
source: 34 m2  40 mg/m2 of enriched isotope
tracking volume: ~ 3000 drift chamber cells
calorimeter: ~ 1000 scintillators + PMTs
1m
5m
Top view
© S. Julian, NEMO-3 collaboration
Full detector ( 2012- )
20 modules: 100 kg of enriched isotope
Needed cavity:
~60 x 15 x 15 m
Location:
14 m
Modane,
Gran Sasso …?
Source foil
Water shield ( 2 ktons)
3,75 m
© S. Julian, LAL
Summary
 observation of 0nbb decay 
Majorana neutrinos
 measurement of T1/2(0nbb) 
nuclear matix element
absolute n mass scale
physics beyond SM
mass hierarchy
 complementary experiments needed and
planned
Most promissing 0nbb projects
A.S. Barabash, arXiv:hep-ex/0602037
Plans for SuperNEMO
2005 - 2007 - R&D program
2008
- construction of the SuperNEMO module with 5 kg 82Se
2009 - 2011 - construction and installation of the 20 modules,
start taking data with delivered modules
2012
- full SuperNEMO running with 100 kg of 82Se
100Mo
2b2n Single Energy Distribution
Single electron spectrum different
between SSD and HSD
HSD, higher levels
contribute to the decay
1
100Tc
SSD, 1 level
Simkovic,
J. Phys. G, 27, 2233, 2001
dominates in the decay
(Abad et al., 1984,
Ann. Fis. A 80, 9)
0
100Mo
Esingle (keV)
NEMO-3
4.57 kg.y
4.57 kg.y
NEMO-3
E1 + E2 > 2 MeV
E1 + E2 > 2 MeV
• Data
• Data
HSD
higher levels
2b2n HSD
Monte Carlo
Background
SSD
Single State
2b2n SSD
Monte Carlo
Background
2/ndf = 40.7 / 36
2/ndf = 139. / 36
Esingle (keV)
HSD: T1/2 = 8.61  0.02 (stat)  0.60 (syst)  1018 y
SSD: T1/2 = 7.72  0.02 (stat)  0.54 (syst)  1018 y
Esingle (keV)
100Mo
2b2n single energy distribution
in favour of Single State Dominant (SSD)
Event selection criteria
• Two tracks of negative charge associated to isolated PM
• Energy deposit in each scintillator E > 200 keV.
• Event vertex is inside the foil
• Distance track-to-vertex: DXY < 4 cm, DZ<8 cm;
• TOF cut: internal hypothesis probality > 4%, external hypothesis
probability<1%;
• Reject events with the alpha particle found using alpha_search means:
• if only 1 extra hit in the tracking detector
• if at least 2 hits
search for a short track
Dt > 2 msec only but all hits on time
Dt > 40 msec
Dxy < 4 cm
DZ < 10 cm
vertex
• Reject events with two tracks at one side of the foil and a geiger
hit in time at the opposite side fo the foil close to the vertex: Möller scattering
of b decay in gas (Radon).
(Qbb ~ MeV)
arbitrary units
Neutrino Ettore Majorana Observatory
NEMO collaboration
CENBG, IN2P3-CNRS et Université de Bordeaux, France
IReS, IN2P3-CNRS et Université de Strasbourg, France
LAL, IN2P3-CNRS et Université Paris-Sud, France
LPC, IN2P3-CNRS et Université de Caen, France
LSCE, CNRS Gif sur Yvette, France
Fes University, Marocco
FNSPE, Prague University, Czech Republic
INEEL, Idaho Falls, USA
ITEP, Moscou, Russia
JINR, Dubna, Russia
JYVASKYLA University, Finland
KURCHATOV Institute, Russia
MHC, Massachusets , USA
Saga University, Japan
UCL London, UK