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NEMO3 experiment: results for 150 Nd

NEMO3 experiment: results for 150 Nd. Gwénaëlle Broudin-Bay LAL (CNRS/ Université Paris-Sud 11) for the NEMO collaboration Moriond conference La Thuile, March 2008. Outline. Double beta decay physics The NEMO3 experiment ββ 2 ν results for 150 Nd Background for 2 β 0 ν

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NEMO3 experiment: results for 150 Nd

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  1. NEMO3 experiment: results for 150Nd Gwénaëlle Broudin-Bay LAL (CNRS/ Université Paris-Sud 11) for the NEMO collaboration Moriond conference La Thuile, March 2008

  2. Outline • Double beta decay physics • The NEMO3 experiment • ββ2ν results for 150Nd • Background for2β0ν • ββ0ν results for 150Nd • Conclusions and perspectives

  3. Double beta decay E (A, Z+1) (A, Z) Qββ ββ (A, Z+2) Double beta decay physics ββ2νdecay (A,Z)  (A,Z+2) +2e- +2 ββ2νdecay is allowed by the Standard Model and has been observed for 9 nuclei (7 studied by the NEMO experiments). (A,Z)  (A,Z+2) +2e- ββ0νdecay 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 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 Arbitrary unit Q Energy sum of the electrons E1+E2 Other mechanisms: right currents (V+A) emission of Majoron SUSY

  6. The NEMO3 experiment 20 secteurs 3 m B(25 G) 4 m Identification of e-, e+, γand α The NEMO3 detector Sources: 10 kg of  emitters 6.914 kg of 100Mo and 0.932 kg of 82Se S = 20 m2, 60 mg/cm2 Tracking volume: Drift chamber (Geiger mode) 6180 cells Gaz: He + 4% ethanol + 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 October 2004

  9. The NEMO3 experiment Longitudinal view Run Number: 2040 Event Number: 9732 Date: 2003-03-20 Transversal view Emission vertex Emission vertex 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 ββevent selection Selection criteria • 2 tracks associated with negatively charged particles • 2 PMTs, 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. ββ2ν results Energy sum of the electrons Angular distribution PRELIMINARY PRELIMINARY ββ2ν results for 150Nd Qββ = 3.367 MeV 46.6 g of Nd2O3 enriched to 91%, equivalent to 37 g of 150Nd Feb 2003 – Dec 2006 : 939 days of data collection 2828 events observed T1/2 (ββ2ν) = (9.20 +0.25-0.22 (stat) ± 0.73 (syst)). 1018 y

  11. ββ2ν results Results of previous experiments ITEP TPC experiment 9 events observed, 38 days, natural Nd2O3 (2.5g of 150Nd) 36 events observed, 53 days, 51.5 g of enriched Nd2O3 (V. Artemiev et al.,Phys. Let. B., 345, (1995) 564) University of California (Irvine) group TPC experiment 476 events observed, 262 days, 15.5 g of Nd2O3 enriched to 91 % in 150Nd (A. De Silva et al., Phys. Rev. C 56 (1997) 2451)

  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 Single e- from foil ββ2ν from foil 2 e- channel from foil Δt = 0 ns Background measurement for ββ0ν

  13. ββ0ν results 150Nd PRELIMINARY ββ0ν MC (T1/2 = 1.45 1022 y) radioactive background MC ββ2νbackground + radioactive background MC Above 2.5 MeV 28.6 ± 2.7 events expected from background 29 events observed ββ0ν results for 150Nd Light Neutrino exchange COLLIE statistical method above 2.5 MeV Detection efficiency: 19% T1/2 (ββ0ν) > 1.45 1022 y 90 % CL <mν> < 3.7 – 5.1 eV V.A. Rodin et al., Nucl. Phys. A 766 (2006) 107 Previous result: T ½ > 1.7 1021 y 90 % CL A.A. Klimenko et al., Nucl. Instr. Meth. B 17 (1986) 445 Right currents: T1/2 (ββ0ν) > 1.27 1022 y 90 % CL Emission of Majoron (M1) : T1/2 (ββ0ν) > 1.55 1021 y 90 % CL

  14. NEMO3 results Summary of NEMO3results * R. Arnold et al., Phys. Rev. Lett. 95 182302 (2005)

  15. 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) ± 0.73 (syst)). 1018 y • The limit on the half-life value for the ββ0ν process has been improved. T1/2 > 1.45 1022 y 90% CL <mν> < 3.7 – 5.1 eV • 150Nd is a good candidate for the SuperNEMO and SNO+ projects: • high Qββ value • large phase space factor Enrichment by laser separation of large masses of 150Nd currently under consideration.

  16. Back up slides

  17. Double beta decay 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 measurement, several isotopes studied at once.

  18. The NEMO3 experiment Background measurement Single e-analysischannel Internal e- - γanalysischannel PRELIMINARY PRELIMINARY PRELIMINARY Energy of the electron Energy of the γ Energy of the electron

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