Neutrino%20Physics%20-%20Lecture%201

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Neutrino Physics - Lecture 1

• Steve Elliott
• LANL Staff Member
• UNM Adjunct Professor
• 505-665-0068, elliotts_at_lanl.gov

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Course Format

• Seminar series on neutrinos
• Student presentations
• Hand out enrollment sheet.

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Lecture 1 Outline

• Prerequisites
• References
• Discussion regarding course
• Connections to other physics
• Neutrinos in the standard model

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Prerequisite TopicsBut, I can cover topics on
request

• Schrodinger level quantum mechanics
• We will make reference to quantum field theory on
  occasion
• Kinematics/Relativity
• Particle Reactions
• Cross Sections
• Radioactivity (???????)
• Energy Loss
• Symmetries (P,C,T, CP, CPT)
• Linear Algebra Basics

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Some References

• hep-ph/0606054, Strumia/Vissani
• APS neutrino study and its working groups
• https//www.interactions.org
• Neutrino Astrophysics - John Bahcall
• The Physics of Massive Neutrinos - Boris Kayser
• Massive Neutrinos in Physics and Astrophysics
  Mohapatra/Pal
• Physics of Massive Neutrinos Boehm/Vogel

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Why are neutrinos relevant?

• Basic Particle Physics
• We know little about the neutrinos properties
• Beyond the Standard Model
• The neutrino is an important ingrediant to
  understanding the inclusion of mass and the
  various energy scales
• Nuclear Physics
• Key to understanding symmetries and interactions
• Astrophysics
• Supernovae
• Cosmology
• Dark matter
• Large scale structure
• Particle, anti-particle asymmetry

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The Standard Model Particles
u up c charm t top ? gamma
d down s strange b bottom g gluon
?e ?? nt W W boson
e electron ? muon ? tau Z Z boson
u up c charm t top ? gamma
d down s strange b bottom g gluon
?1 ?? n? W W boson
e electron ? muon ? tau Z Z boson
u up c charm t top ? gamma
d down s strange b bottom g gluon
?3 ?? n? W W boson
e electron ? muon ? tau Z Z boson
Quarks
Force Carriers
The Neutrinos
Leptons
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Neutrinos mix, therefore

• Neutrinos have mass
• Might have non-zero magnetic moments
• Heavier neutrinos might decay
• Might be Majorana or Dirac
• What are the implications for
• unification, supersymmetry, and extra dimensions?
• possible existence of additional species?
• the possibility that neutrinos have something to
  do with the matter-antimatter asymmetry?

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Why neutrinos are unusual

• Neutrinos might be the ultimate neutral particle
• They would not be distinct from their
  antiparticles.
• If so they would be Majorana particles
• They might also be Dirac particles
• Like the charged quarks and leptons

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Neutrinos and the weak interaction

• The weak interaction violates parity.
• Hence there are no right handed current
  interactions
• This can be interpreted two ways.
• There are no right handed neutrinos
• There are RH neutrinos, they just dont interact

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There are 3 active light neutrinos
The width of the Z decay depends on the number of
channels available for the decay.
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Dirac vs. Majorana
Lorentz
(nDi , nDh)
(nDi , nDh)
CPT
CPT
Lorentz
(nMi , nMh)
bb(0n) addresses Dirac/Majorana nature of n.
CPT
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Field Theory Overview - I

• Field operators obey equations of motion derived
  from a Lagrangian (L) via a variational
  principle.
• If the interaction term in L is small (small
  coupling constant), a perturbative approach is
  used.
• Represent successive terms as Feynman diagrams.

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Field Theory Overview - II, QED L
Free electron
Photon
Interaction Term
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Field Theory Overview - IIIdiagrams resulting
from the QED interaction
e
e
?
?
e-
e-
?
?
e
e
e
e
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Typical Dirac mass term
Quarks and leptons get their mass by a coupling
to the Higgs. Here is an example (the electron)
a Dirac particle.
Mij doesnt have to be diagonal, although it is
for the charged leptons.
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For neutrinos
In the standard model, ?jR (the RH neutrino)
doesnt exist, therefore neutrinos are massless
by construction. Now that we know that neutrinos
have mass, we need to learn how to incorporate
that into the model. There are many possibilities.
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We could simply put in ?jR
The coupling fij doesnt have to be diagonal and
in general it isnt. To find the physical fields,
those of definite mass, we need to diagonalize
Mij.
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Such a term leads to mixing
m? is the ?th diagonal element of the mass matrix
The neutrinos mix.
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Shortcomings

• fij is completely arbitrary
• Doesnt explain why neutrinos are so much lighter
  than their lepton partners.
• We have not included additional possible mass
  terms

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Adding Majorana mass terms

• Ms are nxn matrices for n generations.
• ?R, ?L are n element column vectors from n
  generations.

From NC scattering, We know ML is small
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Diagonalize M
Leads to two eigenvalues m1 (MD)2/MR and m2 MR
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Leads to the seesaw mechanism

• If we take MD to be order of lepton mass, and we
  know that MR is large
• We have two Majorana neutrinos
• One with a mass much less than the leptons
• One which is very heavy.

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Connections to other physics

• Cosmology
• Large scale structure
• Baryon asymmetry
• Nuclear and Particle physics
• Incorporating mass into the standard model
• Astrophysics
• Nucleosynthesis
• Supernova dynamics

Neutrinos are very practical
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A summary of the questions

• Are neutrinos Majorana or Dirac?
• What is the absolute mass scale?
• How small is ?13?
• How maximal is ?23?
• Is there CP violation in the neutrino sector?
• Is the mass hierarchy inverted or normal?
• Is the LSND evidence for oscillation true? Are
  there sterile neutrinos?