Neutrinoless double-beta decay and the SuperNEMO project.

Darren Price

University of Manchesterhttp://www.hep.man.ac.uk/u/darren

24 November, 2004

What is the NEMO project? NEMO = Neutrino Ettore Majorana Observatory Main function is investigating neutrinoless double-

beta decay (0) (also 2) 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 superseded by SuperNEMO

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.

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 <mv> sensitivity:

(0.15-0.5) eV

0 observation gives information about absolute mass scale

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, two neutrinos observed, satisfies lepton number conservation In 0, no neutrinos - implications for Standard Model

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!

What is neutrinoless double-beta decay?

2log

22

0001210

vvvv

MFaT

Half life of 0 given by:

Gives <mv> - estimation of neutrino mass scale

Electron energy plot for 2 and 0 :

ya v17

0 105~ dimensional factor

e

v

v

v

m

m

M

F

0

0 phase space factor

nuclear matrix element

5Q

What is SuperNEMO?

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 E/E=10% at 1MeV (better than NEMO3)

• demonstrated at UCL/Dubna

SuperNEMO is next generation 0 detector

What is SuperNEMO?

Boulby mine - attractive experimental site

Timescale:– 2004-05 Scintillator R&D– 2005-06 Design proposal and prototype– 2007-10 Production– 2009-10 Start taking data– 2014 Planned sensitivity

<mv> sensitivity ~ 0.04eV

What am I doing? New experiment - new problems Figuring out how GEANT models 0/2 including

decay kinematics Detector geometry & materials (tracking, scintillator)

Backscattering results

Energy resolution

Considerations:

-ray effects

BG and energy resolution

Mechanics of detection– lasers for daughter particle?– wires to track electrons?

Active/passive scintillator?

Some results so far...

Backscattered electrons– percentage backscattered – energy distribution

Polystyrene : 2.7% : 669keVCarbon : 1.3% : 564keVYttrium : 4.9% : 803keVLead : 6.6% : 879keVYAP : 3.9% : 738keVUranium : 6.8% : 897keV

Some results so far...

Some results so far...

Neutrinoless double-beta decay and the SuperNEMO project.

Darren Price

University of Manchesterhttp://www.hep.man.ac.uk/u/darren

24 November, 2004