no s is good s sheffield physoc 21/04/2005 jeanne wilson a historical introduction to neutrinoless...
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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