Solar Neutrinos

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Solar Neutrinos

• Learning about the core of the Sun
• Guest lecture Dr. Jeffrey Morgenthaler
• Jan 26, 2006

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Review

• Conventional solar telescopes
• Observe optical properties of the Sun to test
  standard model
• Properties include brightness, color, spectrum,
  Doppler shifts of small patches
• Doppler shifts indicate Sun is ringing like a
  bell
• Tones of bell allow probing of solar interior
  to a point (fig 4.9 in textbook)

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Helioseismology
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Neutrinos

• Basic scientific principle ENERGY CONSERVATION
• Energy in energy out
• Wolfgang Pauli solved a problem using the
  principle of energy conservation
• The answer to his problem the neutrino
• The neutrino gave us another problem
• How to detect neutrinos!

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A little Particle Physics

• Chemistry tells us atoms are made up of
  electrons, protons and neutrons
• Particle physics probes deeper into the nucleus
  finding more fundamental particles leptons and
  quarks
• Leptons electron, muon, tau and associated
  neutrinos, (all come in and varieties)
• Quarks up, down, charm, strange, top, bottom
  (all come in matter and anti-matter varieties)
• Protons and neutrons are built out of 3 quarks
  (combo of up and down) with leptons waiting in
  the wings
• Rules of interaction are complicated

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Nuclear Reactions that involve Neutrinos

• Beta Decay (neutrino discovery)
• Inverse beta-decay (first neutrino detection in
  1956)
• Common neutrino detection scheme
• P-P chain first step
• Boron 8 (occasional solar reaction)

N ? P e- n e
P n e ? N e
N n e ? P e- recoil
P P ? D e n e
8B ? 2 4He e n e
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A look at the numbers

• 2 x 1038 solar neutrinos produced every second
• Almost all make it out of the sun (weakly
  interacting with matter)
• Traveling very near the speed of light (8 min
  travel time to earth)
• 70 billion neutrinos per second in each 1 cm
  square patch on earth
• Idea catch the neutrinos and see if they tell us
  anything about the solar interior

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Neutrino Detector History

• First try in 1963 (Barberton Ohio)
• Debugged technique
• A Chlorine neutrino ? radioactive Argon
• Underground to reduce background from
  non-neutrino events
• Showed bigger detector required

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Homestake Construction (1966 photo)
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Homestake Neutrino Detector Operation

• The Solar Neutrino Unit (SNU) 1 neutrino
  interaction per second per 1036 detector atoms
• Problem 1036 is a lot of atoms (about 240
  million tons of cholrine)
• Homestake could afford 1030 atoms
• Result Homestake counted about 2.5 neutrinos per
  day (2.55 0.25 SNU)
• Based on standard solar model, expected 8 1 SNU
• Solar neutrino problem

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If at first you dont succeed

• Kamiokande was built to look for the spontaneous
  decay of protons and bound neutrons
• Works by detecting flashes of light (Cherenkov
  radiation) from recoil of nuclei
• Maximum speed of light waves is fixed in a
  vacuum, but gets slower when traveling through
  something
• Shock waves happen when a particle travels faster
  than the maximum speed of a wave

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Kamiokande
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Kamiokande II

• Upgrade of Kamiokande
• Detected neutrinos from supernova 1987a
• Started detecting solar neutrinos in 1988
• Definitive direction information by 1991
• Measured ½ as many neutrinos as expected!
• But was sure they were coming from the Sun

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try again
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Gallium-based neutrino detectors

• Use Gallium to detect neutrinos from p-p reaction
  
• GALLEX and SAGE used similar techniques to
  Homestake
• Gallium neutrino ? radioactive Germanium
• Sweep Germanium out of system
• Count radioactive decays
• Expected 132 SNU, measured 75 SNU!

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This is getting ridiculous

• Choose 1
• The standard solar model is wrong
• We dont (didnt) understand neutrinos
• The ability to predict many solar properties just
  starting from a ball of gas and letting nuclear
  reactions, diffusion, and convection take place
  suggests we need to look more closely at neutrinos

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Neutrino Oscillations (MSW effect)

• Lincoln Wolfenstein first to have the idea,
  Stanilaw Mikheyev and Aleksei Smirnov refined
• Using the rules of quantum mechanics MSW predicts
  how neutrinos of different types (flavors) behave
  in the presence of matter
• Electron, Mu, and Tau neutrinos mutate from one
  to another
• Detectors sensitive to electron neutrinos miss
  others, hence the SNU shortfall

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Superkamiokande
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Late-breaking news

• The Japanese-American collaboration announced the
  detection of neutrino oscillations in 1998 by
  looking at neutrinos produced in the atmosphere
• Raymond Davis, Jr. (Homestake) and Masatoshi
  Koshiba (Kamiokande) shared the 2002 Nobel Prize
  in physics for their work in neutrino physics

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Future of Neutrino Astronomy

• Sudbury Neutrino Detector (SNO)
• Verified MSW
• Superkamiokande
• Amanda/ICE Cube

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Amanda/Ice Cube

• Detects neutrinos converting in ice at the south
  pole

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Summary

• Principle of CONSERVATION OF ENERGY led to
  proposal of neutrino by Wolfgang Pauli
• Neutrino flux from sun measured by several
  experiments (in units of SNU) fell short from
  solar model expectations (solar neutrino problem)
• Solar model proves reliable for many thing
• Led to proposal of MSW (neutrino oscillations)
• Solar astronomy helped particle physics

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Next Topic Rotation of the Sun and Magnetic Field

• Review effect of sound speed on waves
• Vacuum cleaner analogy
• Waves propagate faster towards center of Sun
• Refraction (bending) depends on wavelength
• Bigger wheels on vacuum cleaner

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Differential rotation