Neutrinoless doublebeta decay and the SuperNEMO project'

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?

• NEMO Neutrino Ettore Majorana Observatory
• Main function is investigating neutrinoless
  double-beta decay (0?bb) (also 2?bb)
• 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
• Planned to be running until 2007-8 when
  hopefully(!) superseded by SuperNEMO

3
What is the NEMO project?

• Experimentally the double beta decays only
  distinguished by their different electron energy
  spectra

• Constructed to detect emitted electrons from
  isotopes known to produce double beta decay,
  whilst reducing any background effects.

4
What is the NEMO project?

• NEMO3 contains 10kg of isotopes primarily
  including enriched molybdenum (6.9kg)

• Need to measure and tag all types of background
• same principles in SuperNEMO, need to eliminate
  BG
• ltmvgt sensitivity (0.15-0.5)
  eV

• 0?bb observation gives information about absolute
  mass scale

5
What is neutrinoless double-beta decay?

• Double beta decay - nucleus simultaneously
  releases two electrons either with two or no
  neutrinos in the final state
• In 2?bb, two neutrinos observed, satisfies lepton
  number conservation
• In 0?bb, no neutrinos - implications for Standard
  Model

6
What is neutrinoless double-beta decay?

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

7
What is neutrinoless double-beta decay?

• Half life of 0?bb given by

• Gives ltmvgt - estimation of neutrino mass scale
• Electron energy plot for 2?bb and 0?bb

8
What is SuperNEMO?

• SuperNEMO is next generation 0?bb detector

• Much larger design - 100kg isotope (Se-82)
• planar geometry, 4 supermodules
• low BG, 5000 photomultipliers, passive shielding
• 10xNEMO3 (big detector - disadvantage)
• NEMO3 is testing feasibility for SuperNEMO
• need BG only from 2?
• need DE/E10 at 1MeV (better than NEMO3)
• demonstrated at UCL/Dubna

9
What is SuperNEMO?

• Boulby mine - attractive experimental site
• Timescale
• 2004-05 Scintillator RD
• 2005-06 Design proposal and prototype
• 2007-10 Production
• 2009-10 Start taking data
• 2014 Planned sensitivity
• ltmvgt sensitivity 0.04eV

10
What am I doing?

• New experiment - new problems
• Figuring out how GEANT models 0?bb/2?bb including
  decay kinematics
• Detector geometry materials (tracking,
  scintillator)
• Backscattering results

• Energy resolution

11
Considerations

• ?-ray effects
• BG and energy resolution
• Mechanics of detection
• lasers for daughter particle?
• wires to track electrons?
• Active/passive scintillator?

12
Some results so far...

• Backscattered electrons
• percentage backscattered
• energy distribution

13
Some results so far...
14
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