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.