No s is good s

Sheffield Physoc21/04/2005

Jeanne Wilson

A historical introduction to neutrinoless double beta decay

Introducing the Neutrino

A*

A

e-

The Beta Decay Puzzle

Breaks energy and momentum conservation

Wolfgang Pauli, 1930

A*

A

e-

C

DiscoveryLooking for something:• very light, possibly massless• electrically neutral• produced alongside electron. • very weakly interacting

It would take 1019 m (300 light years) of water to absorb a single neutrino.

25 years later • Frederick Reines and Clyde Cowan

Project Poltergeist

n p

e-

e

p n

e+e

Solar Neutrinos

380,000 bottles of cleaning fluid

Inverse Beta DecayCl + e Ar + e-

Extract and measure the amount of argon converted in one month.

expect 10 atoms in 1030!

Some of our neutrinos are missing

Neutrino Oscillations

–Mass difference m2

–Neutrino energy E–Distance travelled L–Mixing angle

)E

LΔm27.1(sin2sin1)(

222 eeP

Neutrino Oscillations

Sudbury Neutrino Observatory

1700 tonnes InnerShielding H2O

1000 tonnes D2O

5300 tonnes Outer Shield H2O

12m Diameter Acrylic Vessel

Support Structure for 9500 PMTs, 60% coverage

Urylon Liner andRadon Seal

Reactions in SNO

NC xx npd

CC epd e p -

How to Observe Neutrinos

Working in a Mine

Going Underground

Construction

Going Underground

Water Purity

Class 2000 Clean Room

Detector Operation

How to Observe Neutrinos

•Deep Underground•Low Radioactive Backgrounds

•Precise Measurements•Detailed Calibrations

Reactions in SNO

NC xx npd

CC epd e p -

SNO Results

1.0 (23%)

0.85 (9%)

0.29 (6%)

CC NC

Standard Solar Model Prediction

= 0.34 0.04CCNC

Neutrino flux

http://arxiv.org nucl-ex/0502021

Neutrino Masses

RelativeMassScale

Mas

s

AbsoluteMassScale

)E

LΔm27.1(sin2sin1)(

222 eeP

Neutrino Nature• Majorana particle

neutrino = antineutrino

•Dirac Particles

Like all other fundamental particles

Particle antiparticle

Double Beta Decay

n p

e-

e

n p

e-

e

0+1+

0+(A,Z)(A,Z+1)

(A,Z+2)

Only 35 isotopes known in nature

First proposed 1935

Maria Goeppet-Mayer 1935

First observed 1987

Neutrinoless Double Beta Decay

n p

e-

n p

e-

e

e

e

e

X

NeutrinoAntineutrino

Only for Majorana neutrinos

Gold-Plated Channel

How to detect double beta decay

2.01.51.00.50.0Sum Energy for the Two Electrons (MeV)

Two Neutrino Spectrum Zero Neutrino Spectrum

1% resolution(2) = 100 * (0)

Choose your isotope:

•Detector technology•High isotopic abundance•High energy release

–Fast rate–Above U and Th background

Measuring neutrino mass

0G0|M0|2m2

<m> ( bE/Mtlive)1/4

Phase space factorNuclear Matrix

element

Background

Energy resolutionMass of isotope

Measuring time

The Ideal Experiment

<m> ( bE/Mtlive)1/4

•Large Mass (~ 1 ton)

•Radiopurity

•Demonstrated Technology

•Easy operation

•Large E release

•High Natural Abundance

•Small Volume:

•source = detector

•Good Energy Resolution

•Background separation

The COBRA experiment

Cadmium-Telluride O-neutrino double-Beta Research Apparatus

Use a large amount of CdTe (CdZnTe) Semiconductor Detectors

Array of 1cm3

CdTe detectors

K. Zuber, Phys. Lett. B 519,1 (2001)

Semiconductors

Insulator Semiconductor Metal

Conduction band

Conduction band

Valence band

Valence band

Energy gap

~6 eV ~1 eV

Free electrons

holes

•Ionising particle creates electron-hole pairs

•Apply electric field – collect electrons and holes

•Amount of charge carriers energy deposited

Isotopes in CdZnTe

Zn70 0.62 1001 ß-ß-Cd114 28.7 534 ß-ß-Cd116 7.5 2805 ß-ß-Te128 31.7 868 ß-ß-Te130 33.8 2529 ß-ß-Zn64 48.6 1096 ß+/ECCd106 1.21 2771 ß+ß+Cd108 0.9 231 EC/ECTe120 0.1 1722 ß+/EC

nat. ab. (%) Q (keV) Decay mode

The Ideal Experiment?

•Large Mass (~ 1 ton)

•Radiopurity

•Demonstrated Technology

•Easy operation

•Large E release

•High Natural Abundance

•Small Volume:

•source = detector

•Good Energy Resolution

•Background separation

Background Separation

0

The COBRA Setup

The Crystals

Shielding

Electronics readout

Calibration

60Co

1332 keV

60Co

1173 keV

137Cs

662 keV

The next step

Ssssummary

• 1931 – Neutrino first hypothesised• 1956 – Neutrino first detected• 2001 – Neutrino mass confirmed• Today...

Plans to search for 0 DecaysT1/2 ~ 1025 years