nicholas i chott phys 730 fall 2011
TRANSCRIPT
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Nicholas I Chott PHYS 730 Fall 2011
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The Standard Model
What is Beta-Decay?
Beta decay leads to ν discovery
Early History of the Double Beta Decay
Why is 0νββ Important?
ββ-Decay
2νββ vs. 0νββ
Conclusion
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16 known particles
12 spin ½ fermions
Quarks & Leptons = Normal Matter
4 spin 1 bosons
Gauge Bosons = Interaction particles
3 generations: 2 quarks/2 leptons
SM predicted 7/16 before discovery:
Charm, top, bottom, ν, gluon, Z0 & W
Theory is good but still has problems
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16 known particles
12 spin ½ fermions
Quarks & Leptons = Normal Matter
4 spin 1 bosons
Gauge Bosons = Interaction particles
3 generations: 2 quarks/2 leptons
SM predicted 7/16 before discovery:
Charm, top, bottom, ν, gluon, Z0 & W
Theory is good but still has problems
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Most common form of radioactive decay
Observed for isotopes of almost every
element excluding heavy nuclei
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Nucleon level:
Quark level:
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Continuous energy spectrum of β-particles
Exp. spin did not match theory
2-body decay: violates conservation of energy and momentum
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1930: Pauli suggests 3-body decay
Neutral, spin ½ with little to no mass
“I have done a terrible thing.
I have postulated a particle that
cannot be detected.” -W. Pauli
1956: Reines and Cowan confirm electron (anti-)neutrino existence
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1935 – M. Goppert-Mayer published paper on “Double Beta-Disintegration”
1937 – E. Majorana suggests neutrino was indistinguishable from anti-neutrino
1937 – Racah suggests using DBD to test Majorana’s theory (0νββ)
Maria Goeppert Mayer Ettore Majorana Giulio Racah
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Rare decay among isobaric nuclei (½ ~ 1018 - 1022 years)
Simultaneously emits 2β particles via intermediate state
(Short lived unobservable quantum state that mediates forbidden transitions)
Only when β-Decay forbidden by energy cons. and/or large change in L
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Rare decay among isobaric nuclei (½ ~ 1018 - 1022 years)
Simultaneously emits 2β particles via intermediate state
(Short lived unobservable quantum state that mediates forbidden transitions)
Only when β-Decay forbidden by energy cons. and/or large change in L
Situation occurs naturally b/c of “pairing” interaction of nuclei with even A
Semi-empirical mass formula:
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Rare decay among isobaric nuclei (½ ~ 1018 - 1022 years)
Simultaneously emits 2β particles via intermediate state
(Short lived unobservable quantum state that mediates forbidden transitions)
Only when β-Decay forbidden by energy cons. and/or large change in L
Situation occurs naturally b/c of “pairing” interaction of nuclei with even A
Semi-empirical mass formula:
Over 60 isotopes capable of DBD, 12 observed:
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From atmospheric, solar, and accelerator data, neutrinos oscillate; therefore, they must have mass:
This data yields mass differences and imply 3-mass eigenstates
Only bounds on the lightest mass eigenstate; at least 0.04 eV
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From atmospheric, solar, and accelerator data, neutrinos oscillate; therefore, they must have mass:
This data yields mass differences and imply 3-mass eigenstates
Only bounds on the lightest mass eigenstate; at least 0.04 eV
Two important pieces of information missing about the neutrino
Are they Majorana or Dirac particles? What is the absolute mass scale?
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From atmospheric, solar, and accelerator data, neutrinos oscillate; therefore, they must have mass:
This data yields mass differences and imply 3-mass eigenstates
Only bounds on the lightest mass eigenstate; at least 0.04 eV
Two important pieces of information missing about the neutrino
Are they Majorana or Dirac particles? What is the absolute mass scale?
0νββ can be used as a tool to answer these fundamental questions
Immediate implication of discovery:
Neutrino is a Majorana particle
Total Lepton number is not conserved
Neutrino mass can be determined
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Allowed by SM and observed exp.
Imposes no requirements on neutrino properties
Several decay modes possible:
Not allowed by SM (L = 2)
Hypothetical/can only happen if:
Mass 0, since helicity has to flip
( : LH Helicity; : RH Helicity)
Neutrino is its own anti-particle:
Decay mode:
2νββ 0νββ
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Neutrino properties are important to fundamental questions in physics
DBD used as a tool to look for currently unknown properties
Majorana or Dirac particle
Determine neutrino mass
This information needed to further adapt understanding of the SM
Many experimental challenges
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Thank you!
Questions?
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