A New Theory of Neutrino Oscillations

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A New Theory of Neutrino Oscillations

• Netta Engelhardt
• 8.19.2009

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Presentation Outline

• The Standard Model of Particle Physics
• Neutrinos in the Standard Model
• Neutrino mass
• Standard theory of neutrino oscillation
• LSND and MiniBooNE anomalies
• A New Theory U(1)B-L Gauge Symmetry
• MINOS
• Summary

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Standard Model of Particle Physics

• Describes 3 of the 4 fundamental forces
• Strong force, mediated by gluons
• Electromagnetic force, mediated by the photon
• Weak force, mediated by W and Z bosons

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SM Families of Particles

• Bosons have integer spin, are either elementary
  (gauge bosons or Higgs), or composite (mesons).
  Gauge bosons are force mediators.
• Fermions (matter particles) have spin in
  multiples of ½, are either elementary (quarks
  colored, or leptons colorless) or composite

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Lepton Generations

• 6 leptons, 6 antileptons
• Classified by quantum number flavor electron,
  muon, tau.

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Neutrinos in the Standard Model

• Electromagnetically neutral leptons
• Handedness (chirality) no right-handed neutrinos
• Higgs field gt neutrinos are massless
• Interact only via the weak interaction

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Neutrino Mass through Neutrino Oscillation

• Experimental fact a neutrino of one flavor at
  t0 may be observed to have another flavor at
  tt.

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Neutrinos have Mass

• If not, then the Hamiltonian is diagonal in the
  flavor basis
• gt Flavors are stationary states
• gt Probability of oscillation 0
• So neutrinos have nonzero mass
• H is diagonal in the mass basis (always)
• Mass and flavor are not simultaneously
  diagonalizable

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Standard Theory of Neutrino Oscillation
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Oscillation Probability

• For a simplified 2x2 case

So the standard oscillation probability has a
periodic dependence on L/E and ?, but no
dependence on chirality or L and E independently.
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LSND and MiniBooNE

• LSND produced mu antineutrinos and detected e
  antineutrinos at a baseline of 30 meters. They
  saw an excess of e antineutrino events beyond
  what is predicted by the standard theory.
• Explanation for LSND add a fourth mass
  eigenstate and otherwise keep the theory the
  same.
• MiniBooNE accelerated mu neutrinos and detected e
  neutrinos at a baseline of 541 meters while
  keeping L/E the same as LSNDs.
• Since ? would be the same, L/E would be the same,
  and the mass squared difference would be the
  same, MiniBooNE was expected to see the same sort
  of excess as LSND.

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LSND and MiniBooNE, cont.

• No such excess was seen at MiniBooNE.
• However, MiniBooNE saw an unexplained excess of e
  neutrinos at very low energies.

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A New Neutrino Theory

• Reconciling LSND and MiniBooNE
• Energy
• Baseline
• Chirality
• Baryon and lepton quantum numbers conservation
  (SM), and violation

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A 5th Fundamental Force

• A new gauge interaction mediated by a new gauge
  boson called the paraphoton.
• Requires neutrinos to be Majorana particles
• Generates a B-L (baryon - lepton ) dependent
  potential
• This potential, VB-L, is sensitive to the
  chirality of a neutrino.
• Sensitive to L and E.
• Weaker than the weak interaction
• Requires 3 additional flavorless neutrinos called
  sterile neutrinos, which have a negative B-L
  potential.

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A Minimalistic 31 Model

• 1 sterile mixing neutrino (the miscetrino) and 2
  sterile non-mixing neutrinos.
• Oscillation probability dependent on L and E.
• What about long baseline?

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MINOS

• MINOS is a long-baseline (734 km) neutrino
  oscillation experiment
• Preliminary MINOS data indicates good agreement
  with this model.
• Our model is able to provide an explanation for
  the otherwise contradictory results of LSND
  neutrinos, LSND antineutrinos, MiniBooNE
  neutrinos, MiniBooNE preliminary antineutrino
  data, preliminary MINOS neutrinos and
  antineutrinos data.

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Numerical Analysis

• ?2 90/(49 DOF) at best fit point

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Summary

• The addition of a spontaneously broken B-L
  symmetry is able to reconcile provide a better
  explanation neutrino oscillation data.
• The full 33 model is expected to find an even
  better fit (more parameters).
• We still need names for the sterile neutrinos.

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Acknowledgments

• I would like to express my sincere thanks to my
  advisor, Ann Nelson, and to Jonathan Walsh for
  guidance and support throughout the duration of
  this project.
• Additional thanks are due to Andrew Lytle for
  helpful conversations and to Jenna Walrath for
  bright ideas.