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
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Introducing the Neutrino
A*
A
e-
The Beta Decay Puzzle
Breaks energy and momentum conservation
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Wolfgang Pauli, 1930
A*
A
e-
C
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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
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Project Poltergeist
n p
e-
e
p n
e+e
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Solar Neutrinos
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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!
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Some of our neutrinos are missing
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Neutrino Oscillations
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–Mass difference m2
–Neutrino energy E–Distance travelled L–Mixing angle
)E
LΔm27.1(sin2sin1)(
222 eeP
Neutrino Oscillations
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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
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Reactions in SNO
NC xx npd
CC epd e p -
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How to Observe Neutrinos
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Working in a Mine
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Going Underground
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Construction
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Going Underground
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Water Purity
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Class 2000 Clean Room
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Detector Operation
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How to Observe Neutrinos
•Deep Underground•Low Radioactive Backgrounds
•Precise Measurements•Detailed Calibrations
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Reactions in SNO
NC xx npd
CC epd e p -
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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
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Neutrino Masses
RelativeMassScale
Mas
s
AbsoluteMassScale
)E
LΔm27.1(sin2sin1)(
222 eeP
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Neutrino Nature• Majorana particle
neutrino = antineutrino
•Dirac Particles
Like all other fundamental particles
Particle antiparticle
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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
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Neutrinoless Double Beta Decay
n p
e-
n p
e-
e
e
e
e
X
NeutrinoAntineutrino
Only for Majorana neutrinos
Gold-Plated Channel
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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)
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Choose your isotope:
•Detector technology•High isotopic abundance•High energy release
–Fast rate–Above U and Th background
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Measuring neutrino mass
0G0|M0|2m2
<m> ( bE/Mtlive)1/4
Phase space factorNuclear Matrix
element
Background
Energy resolutionMass of isotope
Measuring time
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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
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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)
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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
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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
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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
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Background Separation
0
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The COBRA Setup
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The Crystals
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Shielding
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Electronics readout
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Calibration
60Co
1332 keV
60Co
1173 keV
137Cs
662 keV
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The next step
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Ssssummary
• 1931 – Neutrino first hypothesised• 1956 – Neutrino first detected• 2001 – Neutrino mass confirmed• Today...
Plans to search for 0 DecaysT1/2 ~ 1025 years