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NEMO3 experiment: results

NEMO3 experiment: results. G. Broudin-Bay LAL (CNRS/ Université Paris-Sud 11) for the NEMO collaboration Moriond EW conference La Thuile, March 2008. Outline. Double beta decay physics The NEMO3 experiment 2 β 2 ν results Background for 2 β 0 ν 2 β 0 ν results

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NEMO3 experiment: results

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  1. NEMO3 experiment: results G. Broudin-Bay LAL (CNRS/ Université Paris-Sud 11) for the NEMO collaboration Moriond EW conference La Thuile, March 2008

  2. Outline • Double beta decay physics • The NEMO3 experiment • 2β2ν results • Background for2β0ν • 2β0ν results • Conclusions and perspectives

  3. Double beta decay E (A, Z+1) (A, Z) Qββ ββ (A, Z+2) Double beta decay physics ββ2ν decay (A,Z)  (A,Z+2) +2e- +2 ββ2νdecay is allowed by the Standard Model and was observed for 9 nuclei (6 studied by the NEMO experiments) ββ0ν decay (A,Z)  (A,Z+2) +2e- Beyond Standard Model

  4. Double beta decay Light neutrino exchange Phase space factor Nuclear Matrix Element 5 -1 T1/2= F(Qbb,Z)|M|2<mn>2 Effective mass <mν> = m1|Ue1|2 + m2|Ue2|2.eiα1+ m3|Ue3|2.eiα2 |Uei|: Mixing matrix element; α1 et α2: Majorana phases Neutrinoless double beta decay(ββ0ν) • ββ0νprocess: ΔL=2 Violation of the conservation of the lepton number • massive Majorana neutrino • neutrino mass hierarchy Other mechanisms: right currents (V+A) emission of Majoron SUSY

  5. Double beta decay Arbitrary unit Energy sum of the electrons Q E1+E2 Search for double beta decay experimentally Calorimeter HPGe – bolometer Te – scintillator HM, IGEX, CUORICINO Very good efficiency and energy resolution TPC Irvine, Gotthard, EXO Large mass (136Xe) and efficiency Tracking + calorimeter NEMO Direct identification of the electrons, identification of the background, angular mesure, several isotopes studied at once

  6. The NEMO3 experiment 20 secteurs 3 m B(25 G) 4 m Identification of e-, e+,ganda The NEMO3 detector Sources: 10 kg of  emitters 6.914kg de 100Mo and 0,932 kg de 82Se S = 20 m2, 60 mg/cm2 Tracking volume: Drift chamber (Geiger mode) 6180 cells Gaz: He + 4% alcool ethyl + 1% Ar + 0.1% H2O Calorimeter: 1940 plastic scintillators Associated to low-background PMTs Gamma shielding: Iron (18 cm) Neutron shielding: borated water + wood Magnetic field: 25 Gauss

  7. The NEMO3 experiment bb2n 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 background measurement natTe491 g 100Mo6.914 kg Qbb= 3034 keV 82Se0.932 kg Qbb = 2995 keV Cu621 g bb0n ββemitters in NEMO3

  8. The NEMO3 experiment The building of NEMO3 detector at the Laboratoire Souterrain de Modane in 2001 and with the anti-radon tent since December 2004

  9. The NEMO3 experiment Run Number: 2040 Event Number: 9732 Date: 2003-03-20 Transversal view Longitudinal view Emission vertex Deposited energy: E1+E2= 2088 keV Internal hypothesis: (Dt)mes – (Dt)theo = 0.22 ns Common vertex: (Dvertex) = 2.1 mm Emission vertex (Dvertex)// = 5.7 mm ββevents selection Selection criteria • 2 tracks associated with particles with negative charge • 2 PMT, energy deposit greater than 200 keV • PMT-Track association • Common vertex • Internal hypothesis (external event rejection) • No other isolated PMT (γ rejection) • No delayed track (214Bi rejection)

  10. 2β2ν results Energy sum of the electrons Angular distribution ββ2ν results for 150Nd Qββ = 3.367 MeV 40.2 g of enriched Nd2O3 equivalent to 37 g of 150Nd Phases 1 and 2 (Feb 2003 – Dec 2006) : 939 days of data collection 2828 events observed T1/2 (ββ2ν) = (9.20 +0.25-0.22 (stat) ± 0.62 (syst)). 1018 y

  11. ββ2ν results Results of previous experiments ITEP TPC experiment 9 events observed,38 d, natural Nd2O3 (2.5g of 150Nd) 36 events observed, 53 d, 51.5 g of enriched Nd2O3 University of California (Irvine) group TPC experiment 476 events observed, 262 d, 15.5 g of Nd2O3 enriched to 91 % in 150Nd

  12. ββ0ν results Natural radioactivity of the calorimeter and the structure, neutrons One Crossing Electron channel Δt = 3 ns External (e-, γ) channel Δt = 3 ns γ from radiative capture of neutrons Pair creation (e-,e+)int Δt = 0 ns β-γ emitters inside the sources (e-, γ), (e-,2 γ), (e-,3 γ) from foil Δt = 0 ns β emitters in the foils e- from foil ββ2ν from foil 2 e- channel from foil Δt = 0 ns Background measurement for ββ0ν

  13. ββ0ν results ββ0ν MC 150Nd background MC ββ2ν+ background MC ββ0ν results for 150Nd ββ0ν candidates above 2.6 MeV Detection efficiency: 19% 15.5 ± 1.4 events expected from background 13 events observed T1/2 > 1.45 1022 y Previous result: University of California (Irvine) group TPC experiment T ½ > 2.1 1021 y

  14. Conclusion Conclusion and perspectives • The NEMO3 detector is still collecting data. • The following value of the half-life for the ββ2ν decay of 150Nd was obtained: T1/2 (ββ2ν) = (9.20 +0.25-0.22 (stat) ± 0.62 (syst)). 1018 y • The limit on the half-life value for the ββ0ν process has been improved. • 150Nd is a good candidate for the SuperNEMO project: high Qββ value, large phase space factor. Enrichment of large masses of 150Nd currently under consideration.

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