Neutrino Mass

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Neutrino Mass

• By Ben Heimbigner

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Overview of the Presentation

• History of the Neutrino
• Neutrino Oscillations and the relation to mass.
• Observations of Neutrinos
• Super Kamiokande (Super K)
• Sudbury Neutrino Observatory (SNO)

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What is a Neutrino?

• Fundamental particle belonging to the Lepton
  family
• Predicted 1930 by W. Pauli and first observed in
  1956.
• No Strong or Electromagnetic reaction along with
  a very small mass make them hard to detect.
• Three types also called flavors Electron Muon
  and Tau.

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Solar Neutrino Problem

• First Noticed in the 1960s by Ray Davis
• Used a large tank of Perchloroethylene and
  observed the conversion of chlorine to
  radioactive argon
• Major Disagreement (30 of predicted value)
  between the predicted neutrino numbers that
  should be reaching earth and the measured values.
• At the time it was uncertain what was causing
  this major disagreement between theory and
  experiment.

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Current Detection of Neutrinos

• Cherenkov Radiation
• Interaction between sub atomic particles in water
  and Neutrinos.
• Caused when a particle goes faster than the speed
  of light within a medium. The electron moves
  faster than its electric field can propagate
  similar to a sonic boom.
• Common example is when a neutrino hits an
  electron in water.

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Other Methods of Detecting Neutrinos

• Radiochemical
• Rely on the neutrino interacting with a particle
  and changing it into something else such as
  Chlorine into Argon.
• Scintillation
• Particle is absorbed by the substance and then
  substance fluoresces at specific known
  wavelengths.

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Why Does Neutrino Oscillation mean Neutrino Mass.

• The two properties are intrinsically related
• If Neutrinos are oscillating it means they must
  have mass.
• This flavor oscillation is caused because the
  neutrinos cant be in an eigenstate for energy
  and mass at the same time.
• This causes the Neutrinos to have flavor
  oscillations.

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Neutrino Oscillation Math
We start out with two equations describing the
Neutrinos states. Va describes the flavor,
either electron, muon or tau. Vi describes the
neutrino mass, 1, 2 or 3.
Sense Vi are mass eigenstates we can describe
their propagation by standard plane wave
solutions
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Neutrino Oscillation Cont
If we use the ultra relativistic case we can
describe Ei from the previous equation as
Inserting that into our previous equation we have
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Derivation Finished
From the Previous equation we can find out the
probability that a neutrino of one flavor will
oscillate into a different flavor
Whats most important for us is that this term is
dependent on the squared difference of masses
between the two flavors. This means for there to
be oscillations there needs to be neutrino mass.
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How do we Know they are oscillating?

• 1998 Super-Kamiokande
• Detection of Similar numbers of Muon and Electron
  Neutrinos instead of 21 ratio predicted.
• Indicated that some of the Muon neutrinos were
  oscillating into Tau neutrinos.
• Sudbury Neutrino Observatory (SNO)
• Sensitive to electron and total neutrino flux.

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Why is Neutrino Mass a big deal?

• In the Standard Model Neutrinos were considered
  to be Massless.
• However they have been found to have a mass this
  presents us with physics that are outside the
  realm of the Standard Model.
• Previous to recent experiments all other
  observations had supported that neutrinos had
  zero mass.

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Details on Super K

• Massive 50,000 ton cylinder of pure water
• Located 1000m underground within a mine so as to
  isolate the environment from outside interference
  such as cosmic rays.
• 11,200 Photomultiplier tubes contained within for
  detection of light from Cherenkov radiation.

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Super Kamiokande Experiment

• Super-K is a water imaging Cherenekov detector.
• Neutrino comes in and hits an electron creating
  Cherenekov radiation
• Photomultiplier tubes surrounding the water tank
  then pick up the light emitted from Cherenekov
  radiation.

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Outside View of Super K

• Picture From http//www-sk.icrr.u-tokyo.ac.jp/sk/
  index-e.html

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Super Kamiokande
Photo from http//www-sk.icrr.u-tokyo.ac.jp/sk/in
dex-e.html
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Super-K Findings

• They found that there was strong evidence point
  towards a muon to tau neutrino oscillation from
  their atmospheric results instead of other
  possibilities such as sterile neutrinos or no
  oscillations.
• The solar model also found evidence although less
  direct of neutrino oscillations from the night
  day differences.

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SNO

• 9600 PMTs
• Located 2070 meters below ground in Creighton
  mine.
• 1000 tons of heavy water.

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SNO Detector
SNO Detector viewed from the bottom, it is 12
meters in diameter.
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SNO Experiment

• Able to detect three different reactions.

Elastic Scattering (ES)
Charged Current (CC)
Neutral Current (NC)
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SNO Results

• By measuring all three reactions they were able
  to find that there was an excess of Neutral
  current flux over the elastic scattering and
  charged current. This means that there is an
  excess of total neutrinos (measured by NC)
  compared to electron neutrinos (measured by
  charged current).

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Sources

• Super K Web Site http//www-sk.icrr.u-tokyo.ac.j
  p/sk/index-e.html
• SNO Website http//www.sno.phy.queensu.ca/
• http//www.ps.uci.edu/superk/oscillation.html
• Theory Of Neutrino Oscillations
  (http//www.citebase.org/fulltext?formatapplicati
  on2Fpdfidentifieroai3AarXiv.org3Ahep-ph2F040
  9230)
• http//www-sk.icrr.u-tokyo.ac.jp/sk/pub/koshio-pro
  c.pdf
• http//www-sk.icrr.u-tokyo.ac.jp/sk/pub/svoboda-ta
  u2000.pdf
• Various Wikipedia articles.