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NEMO-3 Double Beta Decay Experiment: Last Results

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  1. NEMO-3 Double Beta Decay Experiment: Last Results A.S. Barabash ITEP, Moscow (On behalf of the NEMO Collaboration)

  2. 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

  3. NEMO-3 Double Beta Decay Experiment: Last Results PLAN I. Introduction II. NEMO-3 detector III. Results IV. Conclusion

  4. I. Introduction 0+ _______ ////// 100Tc 0+_______ /////// 100Mo 0+ ______ 2+ ______ 0+ _____ ////// 100Ru 100Mo 100Ru + 2e- 100Mo 100Ru + 2e- + χ0 100Mo 100Ru + 2e- + 2ν Qββ= 3.033 MeV

  5. NEUTRINOLESS DOUBLE BETA DECAY Experimental signature: 2 electrons E1+ E2=Q

  6. 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> = Uej2 eijmj Thus searches for double beta decay are sensitive not only to masses but also to mixing elements and phases j.

  7. 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.

  8. 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.

  9. 20 sectors B(25 G) 3 m Magnetic field: 25 Gauss Gamma shield: Pure Iron (18 cm) Neutron shield: borated water (~30 cm) + Wood (Top/Bottom/Gapes between water tanks) 4 m Able to identify e-, e+, g and a The NEMO3 detector Fréjus Underground Laboratory : 4800 m.w.e. 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

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

  11. bb2n measurement bb0n search bb decay isotopes in NEMO-3 detector 116Cd405 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 130Te454 g Qbb = 2529 keV External bkg measurement natTe491 g 100Mo6.914 kg Qbb = 3034 keV 82Se0.932 kg Qbb = 2995 keV Cu621 g (All enriched isotopes produced in Russia)

  12. Transverse view Run Number: 2040 Event Number: 9732 Date: 2003-03-20 Transverse view Run Number: 2040 Event Number: 9732 Date: 2003-03-20 Longitudinal view Longitudinal view 100Mo foil Vertex emission Geiger plasma longitudinal propagation 100Mo foil Vertex emission Deposited energy: E1+E2= 2088 keV Internal hypothesis: (Dt)mes –(Dt)theo = 0.22 ns Common vertex: (Dvertex) = 2.1 mm Scintillator + PMT (Dvertex)// = 5.7 mm • Trigger: at least 1 PMT > 150 keV •  3 Geiger hits (2 neighbour layers + 1) • Trigger rate = 7 Hz • bb events: 1 event every 2.5 minutes 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

  13. Data • Data 22 Monte Carlo 22 Monte Carlo Background subtracted Background subtracted 100Mo 22 preliminary results (Data Feb. 2003 – Dec. 2004) Angular Distribution Sum Energy Spectrum 219 000 events 6914 g 389 days S/B = 40 219 000 events 6914 g 389 days S/B = 40 NEMO-3 NEMO-3 100Mo 100Mo E1 + E2 (keV) Cos() T1/2 = 7.11± 0.02 (stat) ± 0.54 (syst)  1018 y Phys Rev Lett 95, 182302 (2005) 7.37 kg.y

  14. NEMO-3 932 g 389 days 2750 events S/B = 4 82Se Background subtracted • Data 22 Monte Carlo E1+E2 (keV) NEMO-3 NEMO-3 NEMO-3 37 g 168.4 days 449 events S/B = 2.8 405 g 168.4 days 1371 events S/B = 7.5 5.3 g 168.4 days 72 events S/B = 0.9 116Cd 96Zr 150Nd Data Data Data bb2n simulation bb2n simulation bb2n simulation E1+E2 (MeV) E1+E2 (MeV) E1+E2 (MeV) 22 preliminary results for other nuclei 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 96ZrT1/2 = 2.0 ± 0.3 (stat) ± 0.2 (syst)  1019 y Background subtracted

  15. 48Ca. 22 preliminary result (Esmall > 0.6 or 0.7 MeV, cos(q) < 0.0) Esmall > 0.7 MeV cos(q)<0.0 Esmall > 0.6 MeV cos(q)<0.0 Very Small Background !! T1/2 = [3.9±0.7(stat)±0.6(syst)]·1019 y

  16. HSD, higher levels contribute to the decay SSD simulation 1+ SSD, 1+ level dominates in the decay (Abad et al., 1984, Ann. Fis. A 80, 9) 100Tc 0+ 100Mo Single electron spectrum different between SSD and HSD Simkovic, J. Phys. G, 27,2233, 2001 Esingle (keV) bb results for 100Mo T1/2 = 7.11 ± 0.02 (stat) ± 0.54 (syst)  1018 y Phys. Rev. Lett. 95 (2005) 182302 SSD model confirmed Decay to the excited 0+ state of 100Ru T1/2 = 5.7+1.3-0.9 (stat) ± 0.8 (syst)  1020 y To be published soon bb0n Phase I + II ( 587d) Use MC Limit approach: shape information, different background level for PI and PII E1+E2>2 MeV 12952 evs MC = 12928 ± 70 e0n=18.1 % T1/2 > 5.6∙1023 y, 90% CL Window method [2.78-3.20] MeV, (690d) 14 evs MC = 13.4 e0n=8.2 % T1/2 > 5.8∙1023 y, 90% CL

  17. bb results for 82Se T1/2 = 9.6 ± 0.3 (stat) ± 1.0 (syst)  1019 y Phys. Rev. Lett. 95 (2005) 182302 bb0n Phase I + II ( 587d) Use MC Limit approach E1+E2>2 MeV 238 evs, MC = 240.5 ± 7, e0n=17.6 % T1/2 > 2.7∙1023 y, 90% CL Window method [2.62-3.20] MeV, (690d) 7 evs, MC = 6.4, e0n=14.4 % T > 2.1∙1023 y, 90% CL

  18. Best present results: 0 decay

  19. 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.

  20. Decay with Majoron emission NEMO-3 results * R.Arnold et al. Nucl. Phys. A765 (2006) 483

  21. 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

  22. 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.