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Results of the NEMO-3 experiment (Summer 2009)

Results of the NEMO-3 experiment (Summer 2009). Outline The bb0n decay The NEMO-3 experiment Measurement of the backgrounds bb2n and bb0n results. Xavier Sarazin On behalf of the NEMO-3 Collaboration. 2nd LSM-Extension Workshop - October 16 2009 - Modane, France. p. p. n. n.

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Results of the NEMO-3 experiment (Summer 2009)

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  1. Results of the NEMO-3 experiment (Summer 2009) • Outline • The bb0n decay • The NEMO-3 experiment • Measurement of the backgrounds • bb2n and bb0n results Xavier Sarazin On behalf of the NEMO-3 Collaboration 2nd LSM-Extension Workshop - October 16 2009 - Modane, France

  2. p p n n W- e- W- e- bb2n Standard process n ? bb0n ? nM n e- e- W- n W- n p p bb0n (Energy sum of the two e-) / Qbb Goal of the NEMO-3 experiment: The search for the neutrinoless double beta (bb0n) decay Process beyond the Standard Model - If bb0n decay is observed  the neutrino is a Majorana particle n=n

  3. The NEMO-3 detector 20 sectors 3 m B(25 G)‏ 4 m Modane Underground Laboratory : 4800 m.w.e. Source: 10 kg of  isotopes cylindrical, S = 20 m2, e ~ 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

  4. The NEMO-3 detector Magnetic field: 25 Gauss Gamma shield: Pure Iron (e = 18 cm) Neutron shield: 30 cm water (ext. wall) 40 cm wood (top and bottom) (since march 2004: water + boron) Modane Underground Laboratory : 4800 m.w.e. Source: 10 kg of  isotopes cylindrical, S = 20 m2, e ~ 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

  5. The NEMO-3 detector 20 sectors 3 m Magnetic field: 25 Gauss Gamma shield: Pure Iron (e = 18 cm) Neutron shield: 30 cm water (ext. wall) 40 cm wood (top and bottom) (since march 2004: water + boron) B(25 G)‏ 4 m Radon-free air around the detector • Phase I (Feb 2003 oct. 2004): High Radon • Phase II (Dec 2004 today): Low Radon (Radon cont. reduced by factor 6) Modane Underground Laboratory : 4800 m.w.e. Source: 10 kg of  isotopes cylindrical, S = 20 m2, e ~ 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

  6. bb2n measurement bb0nsearch 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 (Enriched isotopes produced by centrifugation in Russia)

  7. bb event in NEMO3 Transverse view Run Number: 2040 Event Number: 9732 Date: 2003-03-20 Longitudinal view Vertex emission Vertex emission Deposited energy: E1+E2= 2088 keV Internal hypothesis: (Dt)mes –(Dt)theo = 0.22 ns Common vertex: (Dvertex) = 2.1 mm (Dvertex)// = 5.7 mm bb events selection • 2 trackswith charge < 0 • 2 PM, eachE> 200 keV • PM-track association • Common vertex • Internal hypothesis Dt~0ns • No isolated PM(g rejection) • No delayed track (214Bi rejection ) Typical bb2n event observed from 100Mo • Trigger: 1 PM > 150 keV • 3 Geiger hits (2 neighbour layers + 1) • Trigger Rate ~ 5.5 Hz • bb evts: 1 event every 2 minutes

  8. Measurement of the different components of background in NEMO-3 Recent publication in NIM A606 (2009) 449-465)

  9. NEMO-3 Backgrounds for bb • External g(if the g is not detected in the scintillators) • Origin: natural radioactivity of the detector or neutrons • Main bkg for bb2n but negligeable for bb0n • (100Mo and 82SeQbb~ 3 MeV > Eg(208Tl) ~ 2.6 MeV ) • 232Th (208Tl) and 238U (214Bi) contaminationinside the bb source foil 220Rn 218Po++ • Radon (214Bi) inside the tracking detector • - deposits on the wire near the bb foil • - deposits on the surface of the bb foil Each bkg is measured using the NEMO-3 data

  10. Measurement of the external g background Two topologies to measure the components of external g bkg external (e-,g) crossinge-

  11. Measurement of the external g background External g-ray flux model: the simulations fit very well the NEMO-3 data both in (e-,g) and crossing e- channels External (e-,g) channel Crossing e- channel Energy Sum of the two scintillators (MeV) Energy of the single e- (MeV)

  12. Measurement of the Radon inside the tracking detector Pure sample of 214Bi - 214Po events 214Bi on the wires b- 214Bi on the surface of the source foil T1/2=162.9 ms delayed a b a 214Bi → 214Po → 210Pb Delay time of the a track (ms) (164 ms) Monitoring of the Radon bkg every day • Phase 1: Feb. 2003 → Sept. 2004 • Radon Contamination • Phase 2: Dec. 2004 → Today • A (Radon) ≈ 5 mBq/m3 a b- 214Bi  214Po (164 ms)  210Pb

  13. Measurement of the 208Tl (232Th) inside the bb source foil Agreement with HPGe measurements 208Tl contamination in the Mo foils: A(208Tl) ~ 100 mBq/kg  100Mo foils should be measured later inside the BiPo detector 208Tl contamination inside the bb source foils is measured using internal (e-,g,g) or (e-,g,g,g) channels

  14. bb2n and bb0n results (summer 2009)

  15. bb2n result with 100Mo

  16. bb2n results with the other isotopes

  17. bb0n results with 100Mo Tobs = 3.85 years M(100Mo) = 6.914 kg

  18. bb0n results with 82Se Tobs = 3.85 years M(82Se) = 932 g

  19. bb2n ~ 50% Radon (~5 mBq/m3) ~ 30% 208Tl (~100mBq/kq) ~ 20% Summary • NEMO-3 running until end 2010 • The backgrounds have been measured from the experimental data using different topologies of event (NIM A606 (2009) 449-465) • T½(bb2n) measured for 7 isotopes: 48Ca, 82Se, 96Zr, 100Mo, 116Cd, 130Te, 150Nd • Activities of Radon (214Bi) and 208Tl, the two most troublesome sources of bkg for bb0n decay, have been measured with adequate precision. Bkg for 100Mo (Phase 2) in the bb0n energy window [2.8 – 3.2] MeV  bkg ~ 0.5 cts/kg/year • Preliminary results for bb0n with 100Mo and 82Se 100Mo T1/2(bb0n) > 1.1 1024 years (90% C.L.)  <mn> < 0.45 – 0.93 eV • 82Se T1/2(bb0n) > 3.6 1023 years (90% C.L.)  <mn> < 0.89 – 1.61 eV

  20. BACKUP

  21. Summary of the different background components for 100Mo in the bb0n energy window [2.8 – 3.2] MeV Bkg ~ 0.5 cts/kg/year in the bb0n energy window [2.8 – 3.2] MeV

  22. Test of the background measurement with the Cu foils 1 sector is equiped with very pure Copper foils Internal e-,g channel Internal e-,e- channel (bb-like events)

  23. 0of 100Mo [2.8 , 3.2] MeV: Data: 10 events, Expected: 7.4 events Excluded at 90% C.L. 8.3 events Efficiency = 0.0786 [2.8 , 3.2] MeV: Data: 10 events, Expected: 11.2 events Excluded at 90% C.L. 6.1 events Efficiency = 0.0706

  24. 0of 82Se [2.6 , 3.2] MeV: Data: 6 events, Expected: 5.8 events Excluded at 90% C.L. 5.6 events Efficiency = 0.159 [2.6 , 3.2] MeV: Data: 9 events, Expected: 7.4 events Excluded at 90% C.L. 7.4 events Efficiency = 0.148

  25. Summary of the bb0n results obtained with NEMO-3

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