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 2β2 ν results Background for 2β0 ν 2β0 ν results Conclusions and perspectives

3. Double beta decay physics (A,Z)  (A,Z+2) +2e - +2 β β 2ν decay ββ2ν decay is allowed by the Standard Model and was observed for 9 nuclei (6 studied by the NEMO experiments) Double beta decay β β 0ν decay (A,Z)  (A,Z+2) +2e - (A, Z) (A, Z+1) (A, Z+2) E ββ Q ββ Beyond Standard Model

4. Neutrinoless double beta decay (ββ0ν) T 1/2 = F(Q ,Z) |M| 2 2 Phase space factor Nuclear Matrix Element Effective mass = m 1 |U e 1 | 2 + m 2 |U e 2 | 2.e iα 1 + m 3 |U e 3 | 2.e iα 2 |U e i |: Mixing matrix element ; α 1 et α 2 : Majorana phases 5 Light neutrino exchange ββ0ν process: ΔL=2 Violation of the conservation of the lepton number  massive Majorana neutrino  neutrino mass hierarchy Double beta decay Other mechanisms: right currents (V+A) emission of Majoron SUSY

5. Search for double beta decay experimentally Double beta decay Calorimeter HPGe – bolometer Te – scintillator HM, IGEX, CUORICINO Very good efficiency and energy resolution TPC Irvine, Gotthard, EXO Large mass ( 136 Xe) and efficiency Tracking + calorimeter NEMO Direct identification of the electrons, identification of the background, angular mesure, several isotopes studied at once Q  E 1 +E 2 Energy sum of the electrons Arbitrary unit

6. Sources : 10 kg of  emitters 6.914kg de 100 Mo and 0,932 kg de 82 Se S = 20 m 2, 60 mg/cm 2 Tracking volume : Drift chamber (Geiger mode) 6180 cells Gaz: He + 4% alcool ethyl + 1% Ar + 0.1% H 2 O Calorimeter : 1940 plastic scintillators Associated to low-background PMTs Gamma shielding: Iron (18 cm) Neutron shielding: borated water + wood Magnetic field: 25 Gauss Identification of e -, e +,  and  The NEMO3 detector The NEMO3 experiment 3 m 4 m B (25 G) 20 secteurs

7. External background measurement 100 Mo 6.914 kg Q  = 3034 keV 82 Se 0.932 kg Q   keV  0 116 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  2 ββ emitters in NEMO3 The NEMO3 experiment

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

9. ββ events selection The NEMO3 experiment (  vertex) // = 5.7 mm Emission vertex Longitudinal view 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 ( 214 Bi rejection) Deposited energy: E 1 +E 2 = 2088 keV Internal hypothesis: (  t) mes – (  t) theo = 0.22 ns Common vertex: (  vertex)  = 2.1 mm Emission vertex Transversal view Run Number: 2040 Event Number: 9732 Date: 2003-03-20

10. ββ2 ν results for 150 Nd Q ββ = 3.367 MeV 40.2 g of enriched Nd 2 O 3 equivalent to 37 g of 150 Nd Phases 1 and 2 (Feb 2003 – Dec 2006) : 939 days of data collection 2828 events observed 2β2 ν results Energy sum of the electrons Angular distribution T 1/2 (ββ2 ν ) = (9.20 +0.25 -0.22 (stat) ± 0.62 (syst)). 10 18 y

11. Results of previous experiments ITEP TPC experiment 9 events observed,38 d, natural Nd 2 O 3 (2.5g of 150 Nd) 36 events observed, 53 d, 51.5 g of enriched Nd 2 O 3 ββ2 ν results University of California (Irvine) group TPC experiment 476 events observed, 262 d, 15.5 g of Nd 2 O 3 enriched to 91 % in 150 Nd

12. Background measurement for ββ0 ν 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 ββ2 ν from foil 2 e - channel from foil Δt = 0 ns ββ0 ν results

13. ββ0 ν results for 150 Nd ββ0ν candidates above 2.6 MeV Detection efficiency: 19% 15.5 ± 1.4 events expected from background 13 events observed T 1/2 > 1.45 10 22 y ββ2 ν + background MC background MC ββ0 ν MC 150 Nd ββ0 ν results Previous result: University of California (Irvine) group TPC experiment T ½ > 2.1 10 21 y

14. Conclusion and perspectives The NEMO3 detector is still collecting data. The following value of the half-life for the ββ2 ν decay of 150 Nd was obtained: T 1/2 (ββ2 ν ) = (9.20 +0.25 -0.22 (stat) ± 0.62 (syst)). 10 18 y The limit on the half-life value for the ββ0 ν process has been improved. 150 Nd is a good candidate for the SuperNEMO project: high Q ββ value, large phase space factor. Enrichment of large masses of 150 Nd currently under consideration. Conclusion