1. Neutrinoless double-beta decay and the SuperNEMO project. Darren Price University of Manchester http://www.hep.man.ac.uk/u/darren 24 November, 2004

2. What is the NEMO project? n NEMO = Neutrino Ettore Majorana Observatory Main function is investigating neutrinoless double- beta decay (0 ) (also 2 ) n Operates at the Fréjus Underground Laboratory in Savoie, France –NEMO Collaboration working since 1989 NEMO prototypes NEMO3 design began 1994 –about where we are now with SuperNEMO n Planned to be running until 2007-8 when hopefully(!) superseded by SuperNEMO

3. What is the NEMO project? n Experimentally the double beta decays only distinguished by their different electron energy spectra n Constructed to detect emitted electrons from isotopes known to produce double beta decay, whilst reducing any background effects.

4. What is the NEMO project? n NEMO3 contains 10kg of isotopes primarily including enriched molybdenum (6.9kg) n Need to measure and tag all types of background –same principles in SuperNEMO, need to eliminate BG n sensitivity: (0.15-0.5) eV 0 observation gives information about absolute mass scale

5. What is neutrinoless double-beta decay? n Double beta decay - nucleus simultaneously releases two electrons either with two or no neutrinos in the final state In 2, two neutrinos observed, satisfies lepton number conservation In 0, no neutrinos - implications for Standard Model

6. What is neutrinoless double-beta decay? Despite lepton no. violation, 0 could exist if: –Neutrinos had non-zero mass (yes) –Neutrinos are Majorana particles Prevailing belief - 0 exists, good experimental indications, and preferred by theorists! Other processes can explain 0, but only 0 can test Majorana nature of neutrino with absolute mass scale –0 only practical approach to tell if Majorana neutrino exists!

7. What is neutrinoless double-beta decay? Half life of 0 given by: n Gives - estimation of neutrino mass scale Electron energy plot for 2 and 0 : dimensional factor phase space factor nuclear matrix element

8. What is SuperNEMO? n Much larger design - 100kg isotope (Se-82) –planar geometry, 4 supermodules low BG, 5000 photomultipliers, passive shielding –10xNEMO3 (big detector - disadvantage) n NEMO3 is testing feasibility for SuperNEMO –need BG only from 2 –need  E/E=10% at 1MeV (better than NEMO3) demonstrated at UCL/Dubna SuperNEMO is next generation 0 detector

9. What is SuperNEMO? n Boulby mine - attractive experimental site n Timescale: –2004-05 Scintillator R&D –2005-06 Design proposal and prototype –2007-10 Production –2009-10 Start taking data –2014 Planned sensitivity n sensitivity ~ 0.04eV

10. What am I doing? n New experiment - new problems Figuring out how GEANT models 0 /2 including decay kinematics n Detector geometry & materials (tracking, scintillator) n Backscattering results n Energy resolution

11. Considerations: n  -ray effects n BG and energy resolution n Mechanics of detection –lasers for daughter particle? –wires to track electrons? n Active/passive scintillator?

12. Some results so far... n Backscattered electrons –percentage backscattered –energy distribution Polystyrene : 2.7% : 669keV Carbon : 1.3% : 564keV Yttrium : 4.9% : 803keV Lead : 6.6% : 879keV YAP : 3.9% : 738keV Uranium : 6.8% : 897keV

13. Some results so far...

15. Neutrinoless double-beta decay and the SuperNEMO project. Darren Price University of Manchester http://www.hep.man.ac.uk/u/darren 24 November, 2004