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NEMO-3 Double Beta Decay Experiment: Last Results
A.S. Barabash ITEP, Moscow (On behalf of the NEMO Collaboration)
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 IEAP, Czech Technical University, Prague, Czech Republic Charles University, Prague, Czech Republic INL, Idaho Falls, USA ITEP, Moscou, Russia JINR, Dubna, Russia JYVASKYLA University, Finland MHC, Massachusets , USA Saga University, Japan UCL London, UK FMFI, Comenius University, Bratislava, Slovakia
NEMO-3 Double Beta Decay Experiment: Last Results
PLAN
I. Introduction
II. NEMO-3 detector
III. Results
IV. Conclusion
I. Introduction 0+ _______ ////// 100Tc 0+_______ /////// 100Mo
0+ ______ 2+ ______ 0+ _____ ////// 100Ru
Qββ= 3.033 MeV
100Mo 100Ru + 2e-
100Mo 100Ru + 2e- + χ0
100Mo 100Ru + 2e- + 2ν
Experimental signature:
2 electronsE1+ E2=Q
NEUTRINOLESS DOUBLE BETA DECAY
Oscillation experiments Neutrino is massive!!!
However, the oscillatory experiments cannot solve the problem of the origin of neutrino mass (Dirac or Majorana? ) and cannot provide information about the absolute value of mass (because the m2 is measured).
This information can be obtained in 2-decay experiments.
<m> = Uej2 eijmj
Thus searches for double beta decay are sensitive not only to masses but also to mixing elements and phases j.
What one can extract from 2β-decay experiments?
Nature of neutrino mass (Dirac or Majorana?).
Absolute mass scale (value or limit on m1).
Type of hierarchy (normal, inverted, quasi-degenerate).
CP violation in the lepton sector.
Neutrinoless double beta decay is being actively searched, because it is closely related to many fundamental concepts of nuclear and particle physics:
- the lepton number nonconservation; - the existence of neutrino mass and its origin (Dirac or Majorana?); - the presence of right-handed currents in electroweak interactions; - the existence of Majoron; - the structure of Higg's sector; - supersymmetry; - heavy sterile neutrino; - the existence of leptoquarks.
3 m
4 m
B (25 G)
20 sectors Source: 10 kg of isotopes cylindrical, S = 20 m2, 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
Magnetic field: 25 GaussGamma shield: Pure Iron (18 cm)Neutron shield: borated water (~30 cm) + Wood (Top/Bottom/Gapes between water tanks)
The NEMO3 detector Fréjus Underground Laboratory : 4800 m.w.e.
Able to identify e, e, and
isotope foils
scintillators
PMTs
Calibration tube
Cathodic rings Wire chamber
100Mo 6.914 kg Q= 3034 keV
decay isotopes in NEMO-3 detector
82Se 0.932 kg Q= 2995 keV
116Cd 405 g Q= 2805 keV
96Zr 9.4 g Q= 3350 keV
150Nd 37.0 g Q= 3367 keV
Cu 621 g
48Ca 7.0 g Q= 4272 keV
natTe 491 g
130Te 454 g Q= 2529 keV
measurement
External bkg measurement
search (All enriched isotopes produced in Russia)
100Mo foil
100Mo foil
Transverse view
Longitudinal view
Run Number: 2040Event Number: 9732Date: 2003-03-20
Geiger plasmalongitudinalpropagation
Scintillator + PMT
Deposited energy: E1+E2= 2088 keVInternal hypothesis: (t)mes –(t)theo = 0.22 nsCommon vertex: (vertex) = 2.1 mm
Vertexemission
(vertex)// = 5.7 mm
Vertexemission
Transverse view Longitudinal view
Run Number: 2040Event Number: 9732Date: 2003-03-20
Criteria to select 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 ( rejection)• No delayed track (214Bi rejection)
Trigger: at least 1 PMT > 150 keV
3 Geiger hits (2 neighbour layers + 1)
Trigger rate = 7 Hz events: 1 event every 2.5 minutes
Typical 2 event observed from 100Mo
events selection in NEMO-3
(Data Feb. 2003 – Dec. 2004)
T1/2 = 7.11 0.02 (stat) 0.54 (syst) 1018 y
Phys Rev Lett 95, 182302 (2005)
100Mo 22 preliminary results
7.37 kg.y
Cos()
Angular Distribution
219 000 events6914 g
389 daysS/B = 40
NEMO-3
100Mo
E1 + E2 (keV)
Sum Energy Spectrum
219 000 events6914 g
389 daysS/B = 40
NEMO-3
100Mo
Background subtracted
• Data22 Monte Carlo
• Data22 Monte CarloBackground subtracted
Background subtracted
82Se T1/2 = 0.96 0.03 (stat) 0.1 (syst) 1020 y
116Cd T1/2 = 2.8 0.1 (stat) 0.3 (syst) 1019 y (SSD)
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
116Cd 150Nd 96Zr
Data
simulation
Data
simulation
Data
simulation
NEMO-3 NEMO-3NEMO-3 5.3 g168.4 days72 eventsS/B = 0.9
37 g168.4 days449 events
S/B = 2.8
405 g168.4 days
1371 eventsS/B = 7.5
E1+E2 (keV)
E1+E2 (MeV) E1+E2 (MeV) E1+E2 (MeV)
82Se
NEMO-3 932 g389 days
2750 eventsS/B = 4
Background subtracted
• Data22 Monte Carlo
22 preliminary results for other nuclei
T1/2 = [3.9±0.7(stat)±0.6(syst)]·1019 y
48Ca. 22 preliminary result(Esmall > 0.6 or 0.7 MeV, cos < 0.0)
Very Small Background !!Esmall > 0.6 MeV cos0.0 Esmall > 0.7 MeV cos0.0
results for 100Mo
T1/2 = 7.11 0.02 (stat) 0.54 (syst) 1018 yPhys. Rev. Lett. 95 (2005) 182302
SSD model confirmed
HSD, higher levels contribute to the decay
SSD, 1 level dominates in the decay (Abad et al., 1984, Ann. Fis. A 80, 9)
100Mo
0
100Tc
1
Decay to the excited 0+ state of 100RuT1/2 = 5.7+1.3
-0.9 (stat) 0.8 (syst) 1020 yTo be published soon
Phase I + II ( 587d)Use MC Limit approach: shape information, different background level for PI and PIIE1+E2>2 MeV12952 evs MC = 12928 ± 70
TT1/21/2 > 5.6∙10 > 5.6∙102323 y, 90% CL y, 90% CL
Window method [2.78-3.20] MeV, (690d)Window method [2.78-3.20] MeV, (690d)14 evs MC = 13.4 =8.2 %
TT1/21/2 > 5.8∙10 > 5.8∙102323 y, 90% CL y, 90% CL
Simkovic, J. Phys. G, 27, 2233, 2001
Single electron spectrum different between SSD and HSD
Esingle (keV)
SSD simulation
results for 82Se
T1/2 = 9.6 0.3 (stat) 1.0 (syst) 1019 yPhys. Rev. Lett. 95 (2005) 182302
Phase I + II ( 587d)Use MC Limit approach
E1+E2>2 MeV238 evs, MC = 240.5 ± 7,
TT1/21/2 > 2.7∙10 > 2.7∙102323 y, 90% CL y, 90% CL
Window method [2.62-3.20] MeV, (690d)Window method [2.62-3.20] MeV, (690d)7 evs, MC = 6.4, =14.4 %
T > 2.1∙10T > 2.1∙102323 y, 90% CL y, 90% CL
Nuclei T1/2, y <m>, eV
[1-3]
<m>, eV
[4]
Experiment
76Ge >1.91025
≈1.21025(?)
>1.61025
< 0.33-0.84≈ 0.5-1.3(?)
<0.36-0.92
< 0.53-0.59≈ 0.7(?)
<0.58-0.64
HMPart of HM
IGEX
130Te >2.41024 < 0.4-0.8 < 0.9-1.4 CUORICINO100Mo >5.81023 < 0.6-0.9 < 2.1-2.7 NEMO
136Xe >4.51023 < 0.8-4.7 < 2.9-5.6 DAMA
82Se >2.11023 < 1.2-2.5 < 2.6-3.2 NEMO
116Cd >1.71023 < 1.4-2.5 < 3.7-4.3 SOLOTVINO
Best present results: 0 decay
References
[1] F. Simkovic, G. Pantis, J.D. Vergados and A. Faessler, Phys. Rev. 60 (1999) 055502.
[2] S. Stoica and H.V. Klapdor-Kleingrothaus, Nucl. Phys. A 694 (2001) 269.
[3] O. Civitarese and J. Suhonen, Nucl. Phys. A 729 (2003) 867.
[4] V.A. Rodin, A. Faessler, F. Simkovic and P. Vogel, Nucl. Phys. A 766 (2006) 107.
Decay with Majoron emission
n=1 * n=2 * n=3 * n=7 *
100Mo >2.7∙1022
g<(0.4-1.8)∙10-4
>1.7∙1022 >1.0∙1022 >7∙1019
82Se >1.5∙1022
g<(0.7-1.9)∙10-4
>6.0∙1021 >3.1∙1021 >5.0∙1020
* R.Arnold et al. Nucl. Phys. A765 (2006) 483
NEMO-3 results
NEMO-3 expected sensitivity
For 5 years of data:
100Mo: T1/2 ~ 2·1024 y (90% C.L.)
<m> < 0.3 – 1.4 eV
82Se: T1/2 ~ 8 ·1023 y (90% C.L.)
<m> < 0.6 – 1.6 eV
CONCLUSION
1. New strong limits on 2β(0) decay of 100Mo and 82Se have been obtained:
T1/2 > 5.8·1023 y (<mν> < 0.6-2.7 eV) T1/2 > 2.1·1023 y (<mν> < 1.2-3.2 eV) 2. New strong limits on different types of 2β(0νM) decay of
100Mo and 82Se have been obtained. 3. Precise investigation of 2β(2) decay for many nuclei
has been done. 4. Detector has been running under “radon-free” conditions
and all results will be improved in the future.