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 + _______ ////// 100 Tc 0 + _______ /////// 100 Mo 0 + ______ 2 + ______ 0 + _____ ////// 100 Ru Q ββ = MeV 100 Mo  100 Ru + 2e Mo  100 Ru + 2e - + χ Mo  100 Ru + 2e - + 2ν

Experimental signature: 2 electrons E1+ E2=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 m 2 is measured).  This information can be obtained in 2-decay experiments. =   Uej2 e i j m j  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 m 1 ).  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 m 2, 60 mg/cm 2 Tracking detector : drift wire chamber operating in Geiger mode (6180 cells) Gas: He + 4% ethyl alcohol + 1% Ar + 0.1% H 2 O Calorimeter : 1940 plastic scintillators coupled to low radioactivity PMTs Magnetic field: 25 Gauss Gamma 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

100 Mo kg Q  = 3034 keV  decay isotopes in NEMO-3 detector 82 Se kg Q  = 2995 keV 116 Cd 405 g Q  = 2805 keV 96 Zr 9.4 g Q  = 3350 keV 150 Nd 37.0 g Q  = 3367 keV Cu 621 g 48 Ca 7.0 g Q  = 4272 keV nat Te 491 g 130 Te 454 g Q  = 2529 keV  measurement External bkg measurement  search (All enriched isotopes produced in Russia)

100 Mo foil Transverse view Longitudinal view Run Number: 2040 Event Number: 9732 Date: Geiger plasma longitudinal propagation Scintillator + PMT Deposited energy: E 1 +E 2 = 2088 keV Internal hypothesis: (  t) mes –(  t) theo = 0.22 ns Common vertex: (  vertex)  = 2.1 mm Vertex emission (  vertex) // = 5.7 mm Vertex emission Transverse view Longitudinal view Run Number: 2040 Event Number: 9732 Date: 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 ( 214 Bi 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 100 Mo  events selection in NEMO-3

(Data Feb – Dec. 2004) T 1/2 = 7.11  0.02 (stat)  0.54 (syst)  y Phys Rev Lett 95, (2005) 100 Mo 2  2 preliminary results 7.37 kg.y Cos(  ) Angular Distribution events 6914 g 389 days S/B = 40 NEMO Mo E 1 + E 2 (keV) Sum Energy Spectrum events 6914 g 389 days S/B = 40 NEMO Mo Background subtracted Data 2  2 Monte Carlo Data 2  2 Monte Carlo Background subtracted

Background subtracted 82 Se T 1/2 = 0.96  0.03 (stat)  0.1 (syst)  y 116 Cd T 1/2 = 2.8  0.1 (stat)  0.3 (syst)  y (SSD) 150 Nd T 1/2 = 9.7  0.7 (stat)  1.0 (syst)  y 96 Zr T 1/2 = 2.0  0.3 (stat)  0.2 (syst)  y 116 Cd 150 Nd 96 Zr Data  simulation Data  simulation Data  simulation NEMO g days 72 events S/B = g days 449 events S/B = g days 1371 events S/B = 7.5 E 1 +E 2 (keV) E 1 +E 2 (MeV) 82 Se NEMO g 389 days 2750 events S/B = 4 Background subtracted Data 2  2 Monte Carlo 2  2 preliminary results for other nuclei

T 1/2 = [3.9±0.7(stat)±0.6(syst)]·10 19 y 48 Ca. 2  2 preliminary result (Esmall > 0.6 or 0.7 MeV, cos  < 0.0) Very Small Background !! Esmall > 0.6 MeV cos  0.0 Esmall > 0.7 MeV cos  0.0

 results for 100 Mo T 1/2 = 7.11  0.02 (stat)  0.54 (syst)  y Phys. Rev. Lett. 95 (2005) 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) 100 Mo 00 100 Tc 11 Decay to the excited 0 + state of 100 Ru T 1/2 = (stat)  0.8 (syst)  y To be published soon  Phase I + II ( 587d) Use MC Limit approach: shape information, different background level for PI and PII E 1 +E 2 >2 MeV evs MC = ± 70    T 1/2 > 5.6∙10 23 y, 90% CL Window method [ ] MeV, (690d) 14 evs MC = 13.4   =8.2 % T 1/2 > 5.8∙10 23 y, 90% CL Simkovic, J. Phys. G, 27, 2233, 2001 Single electron spectrum different between SSD and HSD E single (keV) SSD simulation

 results for 82 Se T 1/2 = 9.6  0.3 (stat)  1.0 (syst)  y Phys. Rev. Lett. 95 (2005)  Phase I + II ( 587d) Use MC Limit approach E 1 +E 2 >2 MeV 238 evs, MC = ± 7,    T 1/2 > 2.7∙10 23 y, 90% CL Window method [ ] MeV, (690d) 7 evs, MC = 6.4,   =14.4 % T > 2.1∙10 23 y, 90% CL

NucleiT 1/2, y, eV [1-3], eV [4] Experiment 76 Ge >1.910 25 ≈1.210 25 (?) >1.610 25 < ≈ (?) < < ≈ 0.7(?) < HM Part of HM IGEX 130 Te >2.410 24 < < CUORICINO 100 Mo >5.810 23 < < NEMO 136 Xe >4.510 23 < < DAMA 82 Se >2.110 23 < < NEMO 116 Cd >1.710 23 < < SOLOTVINO Best present results: 0 decay

References [1] F. Simkovic, G. Pantis, J.D. Vergados and A. Faessler, Phys. Rev. 60 (1999) [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 * 100 Mo >2.7∙10 22 g<( )∙10 -4 >1.7∙10 22 >1.0∙10 22 >7∙ Se >1.5∙10 22 g<( )∙10 -4 >6.0∙10 21 >3.1∙10 21 >5.0∙10 20 * R.Arnold et al. Nucl. Phys. A765 (2006) 483 NEMO-3 results

NEMO-3 expected sensitivity For 5 years of data: 100 Mo: T 1/2 ~ 2·10 24 y (90% C.L.) < 0.3 – 1.4 eV 82 Se: T 1/2 ~ 8 ·10 23 y (90% C.L.) < 0.6 – 1.6 eV

CONCLUSION 1. New strong limits on 2β(0) decay of 100 Mo and 82 Se have been obtained: T 1/2 > 5.8·10 23 y ( < eV) T 1/2 > 2.1·10 23 y ( < eV) 2. New strong limits on different types of 2β(0νM) decay of 100 Mo and 82 Se 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.